Dissertations / Theses: 'Materials - Ductility'

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Wolff, Ira M. "Ductility in high chromium super-ferritic alloys." Doctoral thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/22200.

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Includes reprints of author's related articles.
Bibliography: pages 187-201.
The competition between microfracture and plastic flow has been studied in relation to the thermomechanical processing parameters and minor element chemistry of wrought super-ferritic alloys based on a composition of Fe-40wt% Cr. These alloys have been developed for corrosion-resistant applications, specifically by micro-alloying with platinum group metals to induce cathodic modification, but their use has been hampered by inadequate toughness at ambient temperatures. Brittle cleavage of the alloys is a consequence of the high resistance to plastic flow required to accommodate local stresses, such as those found ahead of a loaded crack. Once initiated, a crack propagates in a brittle manner with minimal ductility. The impact toughness therefore relies on the ability of the alloys to withstand crack initiation. The frequency of the crack initiation events is related to the distribution of secondary phases within the matrix and at the grain boundaries. A direct means of improving the toughness and the ductility is accordingly via annealing cycles and minor alloying additions to control the precipitation of second phases. The ductility is enhanced by raising the mobile dislocation density, and this may be achieved by pre-straining recrystallised material, or increasing the number of dislocation sources in the otherwise source-poor material. The generation of mobile dislocations by prismatic punching at second phase particles in response to local or tessellated stresses was found to increase the ductility and the impact toughness of the alloy. The addition of nickel also increases the brittle fracture resistance by promoting stress accommodation at the crack tip, a result which can, in principle, be explained on the basis of enhanced dislocation dynamics. The tendency of the alloys to form a stable recovered substructure was identified as a critical parameter for both the mechanical and corrosion properties. The low-angle dislocation sub-arrays contribute to overall strain-hardening, but destabilise the passivity of the alloys in acid media. In practice, rationalisation of the microstructural parameters has enabled the practicable fabrication of tough, corrosion-resistant alloys, suitable for commercial development.

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Sheldon, Jerry W. "Growth of semi-elliptical surface cracks in ductile materials." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/17876.

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AHMAD, SAJJAD. "Innovative mix design of cementitious materials for enhancing strength and ductility." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2604771.

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Cement based composites i.e. paste, mortar and concrete are the most utilized materials in the construction industry all over the world. Cement composites are quasi-brittle in nature and possess extremely low tensile strength as compared to their compressive strength. Due to their low tensile strength capacity, cracks develop in cementitious composites due to the drying shrinkage, plastic settlements and/or stress concentrations (due to external restrains and/or applied stresses) etc. These cracks developed at the nanoscale may grow rapidly due to the applied stresses and join together to form micro and macro cracks. The growth of cracks from nanoscale to micro and macro scale is very rapid and may lead to sudden failure of the cement composites. Therefore, it is necessary to develop such types of cement composites possessing higher resistance to crack growth, enhanced flexural strength and ductility. The development of new technologies and materials has revolutionized every field of science by opening new horizons in production and manufacturing. In construction materials, especially in cement and concrete composites, the use of nano/micro particles and fibers in the mix design of these composites has opened new ways from improved mechanical properties to enhanced functionalities. Generally, the production or manufacturing processes of the nano/micro sized particles and fibers are energy intensive and expensive. Therefore, it is very important to explore new methods and procedures to develop less energy intensive, low cost and eco-friendly inert nano/micro sized particles for utilization in the cement composites to obtain better performance in terms of strength and ductility. The main theme of the present research work was to develop a family of new type of cementitious composites possessing superior performance characteristics in terms of strength, ductility, fracture energy and crack growth pattern by incorporating micro sized inert carbonized particles in the mix design of cementitious composites. To achieve these objectives the micro sized inert carbonized particles were prepared from organic waste materials, namely: Bamboo, coconut shell and hemp hurds. For comparison purposes and performance optimization needs, another inorganic waste material named as carbon soot was also investigated in the present research. The experimental investigations for the present study was carried out in two phases; In the first phase of research work, a methodology was developed for the synthesis of the micro sized inert carbonized particles from the above mentioned organic raw materials. In the second phase of research, various mix proportions of the cementitious composites were prepared incorporating the synthesized micro sized inert carbonized particles. For micro sized inert carbonized particles obtained from bamboo and coconut shell three wt.% additions i.e. 0.05, 0.08, 0.20 were investigated and for particles synthesized from hemp hurds 0.08, 0.20, 1.00 and 3.00 wt.% additions were explored. The cement composites were characterized by third-point bending tests and their fracture parameters were evaluated. The mechanical characterization of specimens suggested that 0.08 wt.% addition of micro sized inert carbonized bamboo particles enhances the flexural strength and toughness of cement composites up to 66% and 103% respectively. The toughness indices I5, I10 and total toughness of the cement composites were also enhanced. The carbonized particles synthesized from coconut shell resulted in improved toughness and ductility without any increase in the modulus of rupture of the cement composite specimens. Maximum enhancements in I5 and I10 were observed for 0.08% addition of both carbonized and carbonized-annealed particles. For the carbonized hemp hurds cement composites the results indicate that the micro sized inert carbonized particles additions enhanced the flexural strength, compressive strength and the fracture energy of the cement composites. The microstructure of the cement composites was also studied with the help of field emission scanning electron microscope (FESEM) by observing small chunks of cement composite paste samples. The FESEM observations indicated that the micro sized inert carbonized particles utilized in the mix design of these mixes were well dispersed in the cement matrix. It was also observed that the fracture paths followed by the cracks were tortures and irregular due the presence of micro particles in the matrix. The cracks during their growth often contoured around the inert particle inclusions and resulted in enhanced energy absorption capacity of the cement composites. The study was further enhanced to the cement mortar composites and their performances were studied. The results indicated that the energy absorption behavior of the composites was enhanced for all the cement composites containing micro carbonized particles. Finally, it is concluded that the ductility and toughness properties of the cement composites can be enhanced by incorporating the micro sized inert carbonized particles in the cement matrix. The fracture energy, ductility and toughness properties enhancement of the cement composites greatly depends upon the source and synthesis procedure followed for the production of micro sized inert carbonized particles.

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Zarandi, Faramarz MH. "The effect of high temperature deformation on the hot ductility of Nb-microalloyed steel /." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85109.

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Low hot ductility at the straightening stage of the steel continuous casting process, where the surface temperature ranges from 600 to 1200°C, is associated with transverse cracking on the billet surface. This is attributed to various microalloying elements, which are essential for the mechanical characteristics of the final products. Thermomechanical processing is a new approach to alleviate this problem. In this work, two grades of Nb-containing steel, one modified with B, were examined. In order to simulate the key parameters of continuous casting, specimens were melted in situ and subjected to thermal conditions similar to that occurring in a continuous casting mill. They were also deformed at different stages of the thermal schedule. Finally, the hot ductility was evaluated at the end of the thermal schedule, corresponding to the straightening stage in continuous casting at which the hot ductility problem occurs in the continuous casting process.
The results showed that the presence of B is noticeably beneficial to the hot ductility. Failure mode analysis was performed and the mechanism of fracture was elaborated. As well, the potential mechanisms under which B can improve the hot ductility were proposed.
Deformation during solidification (i.e. in the liquid + solid two phase region) led to a significant loss of hot ductility in both steels. By contrast, deformation in the delta-ferrite region, after solidification, was either detrimental or beneficial depending on the deformation start temperature.
The hot ductility was considerably improved in the steel without B when deformation was applied during the delta → gamma transformation. The effect of such deformation on the other steel grade was not significant. Examination of the microstructure revealed that such improvement is related to a grain refinement in austenite. Therefore, the effect of deformation parameters was studied in detail and the optimum condition leading to the greatest improvement in the hot ductility was determined.
Finally, some solutions to the industrial problem in the continuous casting process were proposed.

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Sjöström, Julia, and Helena Åkesson. "Investigation of Ductility Dip at 1000˚C in Alloy 617." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209823.

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Alloy 617 displays a ductility dip during straining at exactly 1000˚C, leading to brittle fracture. A sudden decrease in ductility appearing during Gleeble hot ductility tests of Ni-based superalloys is a well-known phenomenon, while its cause is unknown. Many mechanisms have been established as possible contributors to the issue, and in later years not one, but the simultaneous presence of several of these mechanisms were confirmed as the cause. The ductility dip leads to solid state cracking and a specific solid state cracking phenomenon known as ductility dip cracking is specifically common in Ni-based superalloys. Ductility dip cracking is identified by intergranular cracks and the occurrence of specific precipitates, among other things. This work investigates the possibility that the decreased ductility is due to ductility dip cracking. Furthermore, other possible explanations are investigated. Visual examination was conducted through LOM, SEM and chemical analysis using EDS technique. Combined with thermodynamic calculations, the existence of Cr-rich M23C6 carbides, Ti(N,C) and Mo-rich particles, most likely M3B2, were confirmed. Further, it is established that the ductility dip is related to the lack of dynamic recrystallization at 1000˚C. It is not confirmed that the ductility dip in alloy 617 is due to ductility dip cracking.
Nickelbaslegeringen 617 uppvisar en minskning i duktilitet under Gleeble-dragprovning vid exakt 1000˚C vilket leder till sprött brott. En plötslig sänkning av duktiliteten vid varmdragning av Ni-baserade superlegeringar är ett välkänt fenomen, dock är orsaken inte fastställd. Många mekanismer har bekräftats som bidrag till problemet och under de senaste åren har den simultana närvaron av fler av dessa mekanismer bekräftats som orsaken. Sänkningen i duktilitet leder till sprickbildning i fast fas och en specifik typ av sprickbildning känd som ”ductility dip cracking” är speciellt förekommande i Ni-bas legeringar. Denna identifieras bland annat genom intergranulära sprickor och närvaron av specifika utskiljningar. Detta arbete undersöker möjligheten att duktilitetssänkningen beror på ”ductility dip cracking”. Dessutom undersöks fler tänkbara förklaringar. Visuell granskning genomfördes via LOM och SEM och analys av sammansättningar via EDS-analys. I kombination med termodynamiska simuleringar blev förekomsten av Cr-rika M23C6 karbider, Ti(N,C) och Mo-rika partiklar, troligtvis M3B2, bekräftad. Fortsatt är det bekräftat att duktilitetssänkningen är relaterat till avsaknaden av rekristallisation vid 1000˚C. Det är inte bekräftat i detta arbete att duktilitetssänkningen i legering 617 beror av ”ductility dip cracking”.

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Johnson, Luke. "Solidification Cracking and Ductility-Dip Cracking Resistance of Ni-Base Filler Metal 52XL with Tantalum and Molybdenum Additions." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1575462956102374.

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Li, Jianjun, and 李建军. "Theoretical modelling and numerical simulation of plastic deformation of nanostructured materials with high strength and ductility." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50605707.

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Nanostructured materials have attracted intensive scientific interests during the past two decades due to their outstanding physical and mechanical properties. However, the brittleness of nanostructured materials posed a great challenge for their engineering applications. Recently, several strategies were successfully adopted to produce nanostructured materials with both high strength and ductility such as surface-nanocrystallized (SNC) materials, nanocrystalline materials with stress-induced nanograin growth and nanotwinned metals. A lot of molecular dynamics (MD) simulations, modelling and experiments have been conducted to investigate the deformation mechanisms and the correlated exceptional mechanical properties and considerable progress has been made. However, some problems remain unsolved. For example, the complicated structure of SNC materials due to its grain size gradient (GSG) surface layer makes it difficult to establish a quantitative model for prediction of their strength and ductility; the main mode of nanograin growth in nanostructured materials, i.e., shear-coupled migration of grain boundaries (GBs), was experimentally observed as contributing to their enhanced ductility, but the mechanism of the enhancement remains unclear. In addition, there exist contradictory results for the grain size dependence of transitional twin thickness that corresponds to the maximum strength of nanotwinned metals. All these issues should be addressed to gain a better understanding of the mechanism-ductility correlation in order to provide some guidelines for designing lighter, stronger and ductile nanostructured materials. Therefore, an attempt was made to study the plastic deformation of nanostructured materials with high strength and ductility by theoretical modelling and numerical simulations. Firstly, the enhanced balance of strength and ductility of SNC materials was studied using a combination of theoretical analysis and finite element simulation. A criterion was established for determining the ductility of SNC materials. The results obtained showed that the ductility of a SNC sample could be comparable to that of its coarse-grained counterpart, while it simultaneously possessed a much higher strength than that of the latter if optimal GSG thickness and topmost phase grain size were adopted. Then a dislocation-density-based model was proposed to quantitatively predict the plastic deformation of SNC materials; the stress-driven nanograin growth was also incorporated in the said model. The capability of the model in predicting the strength and work hardening of SNC materials was validated by the existing experimental results. Thirdly, physical models for shear-coupled migration of GBs in nanostructured materials were developed to explain the general coupling between the shear and the normal migration of GBs observed in MD simulations and experiments. The coupled migration process was found to be a general and effective toughening mechanism in nanostructured materials. Moreover, our study showed that the shear-coupled migration is able to enhance the intrinsic ductility considerably when it cooperates with GB sliding. Finally, an elastic-viscoplastic constitutive model based on the competition of intra-twin and twin-boundary-mediated deformation mechanisms was proposed to predict the grain size dependent transitional twin thickness of nanotwinned metals. A linear relation between the transitional twin thickness and the grain size was predicted, which was in excellent agreement with the results obtained from MD simulations and experiments available in the literatures.
published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy

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Ostrowsky, Jennifer. "A New Approach for Evaluating the Ductility, Volumetric Stiffness, and Permeability of Cutoff Wall Backfill Materials." DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7680.

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The use of plastic concrete for cutoff walls in dams for remediation of seepage issues has become more widely used in the past 25 years, however, the in-situ material properties are still not well understood. The research presents a new testing procedure that combines two existing testing methods, triaxial shear and permeability testing. By developing this laboratory testing method, material properties of the cutoff wall backfill material can be more accurately examined and explained using changes in the permeability of the material to discern the ductility and stiffness.

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Whittaker, Jarrod Talbott. "Ductility and Use of Titanium Alloy and Stainless Steel Aerospace Fasteners." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5796.

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The main purpose of this thesis is to investigate the ductility and application of titanium alloys, like titanium 6Al-4V, when used in aerospace fasteners compared to more conventional stainless steel aerospace fasteners such as A286. There have been concerns raised about the safe usability of titanium 6-4 in the aerospace industry due to its lack of strain hardening. However, there is a lack of data pertaining to this concern of safe usage which this thesis aims to address. Tensile tests were conducted to find the ductility indexes of these fasteners which quantify the amount of plastic to elastic elongation. From the tests conducted it was found that the two materials yield and tensile strengths were very similar, though the ductility index of A286 is on average ten times greater than that of titanium 6-4. This thesis includes joint diagram examples that analyze typical joints using both materials. It was found from joint diagram examples that the lower ductility index of the titanium alloy will only be detrimental to use at higher preloads. However, the titanium alloy can be used safely in place of A286 in most loading situations just with narrower safety margins in these controlled examples.

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Palkovic, Steven D. (Steven David). "Development of a portable scratch test device for probing strength, ductility and structural distress in metal materials." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90157.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Practicing civil, mechanical, aerospace, petroleum and structural engineers are often faced with the complexity of evaluating the quality and integrity of new or existing structures. Recent academic research has demonstrated that instrumented scratch testing is a viable alternative for determining the strength and ductility of metals without the use of destructive methods involving the extraction of tensile testing specimens. Although the scientific basis for scratch testing is well established, there is a necessity for a simple and robust implementation that avoids the complexities of current methods which require expensive laboratory equipment and sophisticated data processing. A detailed description of the instrumented scratch testing method for characterizing ductile metals is provided, as well as comparisons with existing alternatives. An innovative scratch testing method is proposed and validated to perform a displacement controlled scratch experiment. A portable scratch testing device is designed and developed to utilize the displacement control technique along with specific instrumentation to allow for the continuous measurement of material properties along the length of a scratch during the experiment. The scratch testing device and method are implemented in a scratch experiment on a welded connection. For the first time, a simple experimental procedure allows for the measurement of changes in mechanical properties through the weld, from the base metal, heat-affected zone (HAZ) and filler weld metal. This novel application highlights the unique ability of the scratch testing method to monitor the evolution of localized mechanical properties in areas of interest to practicing engineers. Recommendations for future iterations of the portable scratch tester are provided.
by Steven D. Palkovic.
S.M.

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Poerschke, David L. "Mechanical Properties of Oxide Dispersion Strengthened Molybdenum Alloys." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1238018041.

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Cardoso, Geraldo I. S. L. "The influence of microstructure on the hot ductility of four low carbon steels with respect to transverse crack formation in continuously cast slabs /." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59567.

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The influence of Al, Mn and Ti on the hot ductility of four low C steels has been examined.
Ductility troughs were exhibited by all the steels. These could be related to the austenite-to-ferrite phase transformation and grain boundary precipitation behavior. When no precipitation took place at the austenite grain boundaries, the trough occurred by intergranular failure. Fracture surfaces revealed microvoid coalescence, with voids associated with MnS inclusions.
Increasing the Mn in the steels lowers the $ gamma to alpha$ transformation temperature, causing the trough to be moved to lower temperatures. It also decreases the volume fraction of MnS inclusions within the ferrite film. Increasing the Al level caused AlN to be precipitated at the austenite grain boundaries, extending the trough to higher temperatures into the single phase austenite region.
The addition of Ti results in a fine austenite grain size after the solution treatment and impedes AlN precipitation. This leads to improved ductility in the austenite region.
When austenite recrystallization occurs during deformation, any voids which have initiated at the boundaries are trapped within the newly recrystallized grains. Intergranular failure cannot progress and the ductility is high.

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Hope, Adam T. Hope. "Development of a High Chromium Ni-Base Filler Metal Resistant to Ductility Dip Cracking and Solidification Cracking." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461175457.

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Do, Xuan Nam. "Localized failure in dynamics for brittle and ductile materials." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2356.

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La défaillance des matériaux et structures d'ingénierie peut être considéré comme le résultat d'une interaction complexe entre différents phénomènes physiques tels que la nucléation des cavités, les microfissures, les microvides et d'autres processus irréversibles. Ces micro-défauts se fondent éventuellement en une ou plusieurs macro-fissures conduisant à une diminution de la capacité portante et finalement à une défaillance de la structure considérée. La prévention des défaillances des structures et des composants structurels a toujours été un sujet important et une préoccupation majeure en ingénierie. Cette thèse vise à représenter une défaillance localisée dans des matériaux non linéaires sans dépendance de maillage. Un intérêt particulier sera le cas de l’adoucissement dynamique des déformations. Les phénomènes localisés sont pris en compte en utilisant l'approche des discontinuités embarquées fortes dans laquelle le champ de déplacement est amélioré pour capturer la discontinuité. Sur la base de cette approche, on a d'abord développé un modèle unidimensionnel de barres élasto-plastique capable de représenter une défaillance pour des matériaux ductiles avec un durcissement combiné dans une zone de processus de fracture FPZ et un adoucissement avec des discontinuités fortes encastrées. Les résultats comparant le modèle unidimensionnel proposé aux travaux (semi-) analytiques sont présentés. Il a été démontré que la stratégie proposée offre des solutions indépendantes de maillage. La déformation augmente dans le domaine de l’adoucissement avec une diminution simultanée de la contrainte. Le problème se décharge élastiquement à l'extérieur de la zone d’adoucissement de déformation. L'énergie dissipée se trouve à disparaître. Le modèle a également été comparé à un modèle de dommage unidimensionnel capable de représenter la fracture dynamique de la barre d'endommagementélasto-endommagée dans la zone de traitement de fracture - FPZ et de adoucissement avec de discontinuités fortes encastrées pour trouver un bon accord entre deux modèles. Un modèle d'éléments finis bidimensionnel a été développé, capable de décrire à la fois le mécanisme de dommage diffus accompagné d'un durcissement initial et d'une réponse d’adoucissement ultérieure de la structure. On a analysé les résultats de plusieurs simulations numériques effectuées sur des essais mécaniques classiques sous des charges progressivement croissantes telles que le test Brésilien ou le test de flexion en trois points. Le cadre de dynamique proposé est montré pour augmenter la robustesse de calcul. On a constaté que la direction finale des macro-fissures est assez bien prédite et que l'influence des effets d'inertie sur les solutions obtenues est assez modeste notamment en comparaison entre différentes mailles. Ce modèle bidimensionnel a été étendu plus loin dans le modèle bidimensionnel de discontinuité intégrée en viscodamage pour aider à explorer brièvement la mise en œuvre du schéma de point intermédiaire de second ordre qui peut fournir des résultats améliorés sous limitation de la régularisation visqueuse du modèle de dégâts localisés
Failure of engineering materials and structures can be considered as a result of a complex interplay between different physical phenomena such as nucleation of cavities, microcracks,microvoids and other irreversible processes. These micro-defects eventually coalesce into one or more macro-cracks leading to a decrease in the load-bearing capability and finally, to failure of the structure under consideration. Prevention of failure of structures and structural parts has always been a critical subject and a major concern in engineering. This thesis aims to represent localized failure in non linear materials without mesh dependency. Of special interest will be the case of dynamic strain-softening. Localized phenomena are taken into account by using the embedded strong discontinuities approach in which the displacement field is enhanced to capture the discontinuity. Based upon this approach, a one-dimensional model for elasto-plastic bar capable of representing failure for ductile materials with combined hardening in FPZ-fracture process zone and softening with embedded strong discontinuities was first developed. Results comparing the proposed one-dimensional model to (semi-) analytical works are presented. It was shown that the proposed strategy provides mesh independent solutions. Strain increases in the softening domain with a simultaneous decrease of stress. The problem unloads elastically outside the strain softening region. The strain energy is found to vanish. The model was also compared with a one dimensional damage model capable of representing the dynamic fracture for elasto-damage bar with combined hardening in fracture process zone - FPZ and softening with strong embedded discontinuities to find a good agreement between two models. A two-dimensional finite element model was developed, capable of describing both the diffuse damage mechanism accompanied by initial strain hardening and subsequent softening response of the structure. The results of several numerical simulations, performed on classical mechanical tests under slowly increasing loads such as Brazilian test or three-point bending test were analyzed. The proposed dynamics framework is shown to increase computational robustness. It was found that the final direction of macro-cracks is predicted quite well and that influence of inertia effects on the obtained solutions is fairly modest especially in comparison among different meshes. This two-dimensional model was expanded further into the two dimensional continuum viscodamage-embedded discontinuity model to help briefly explore the implementation of the second order mid-point scheme that can provide improved results under limitation of viscous regularization of localized failure damage model

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Guerrero, Garcia José Manuel. "Micromechanical modelling of hybrid unidirectional composite materials under fibre tensile loading." Doctoral thesis, Universitat de Girona, 2020. http://hdl.handle.net/10803/669043.

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In this thesis, a micromechanical model for predicting the tensile failure process in hybrid and non-hybrid unidirectional composite materials under fibre tensile loading is developed. Derived from this, the influence that different parameters have on the failure development in hybrid composites is investigated. The results prove that the model captures qualitatively well the failure development of composite materials. Moreover, adding matrix yielding and dynamic effects into the model allows to improve the modelling predictions compared with experimental results. It is also proved that the size of the material has a significant influence on the hybrid properties, and the dispersion of the fibres in the hybrid material has a large importance on the failure and damage development. Therefore, this thesis gives a step forward towards the inclusion of hybrid composites into commercial design and the generation of more optimised materials
En aquesta tesi, es desenvolupa un model micromecànic per predir el procés de ruptura a tracció de materials compostos unidireccionals híbrids i no híbrids sotmesos a càrregues longitudinals. Derivat d’això, la influència que diferents paràmetres tenen, en el procés de ruptura de materials híbrids, és investigada. Els resultats demostren que el model captura qualitativament el procés de trencament en materials compostos. A més, afegir plasticitat a la matriu i efectes dinàmics en el model permet millorar les prediccions del model comparat amb resultats experimentals. També es demostra que la mida del material té una influència significativa en les propietats híbrides, i que la dispersió de les fibres en el material híbrid té una gran importància en el trencament i el desenvolupament de dany. Per tant, aquesta tesi dóna un pas endavant cap a la inclusió de compostos híbrids en el disseny comercial i la generació de materials més optimitzats

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Yaqub, Muhammad. "Axial compressive and seismic shear performance of post-heated columns repaired with composite materials." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/axial-compressive-and-seismic-shear-performance-of-postheated-columns-repaired-with-composite-materials(76babab7-06db-49b2-a8be-e76c17495eaa).html.

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In the light of extreme events of natural disasters (earthquakes or hurricanes) and accidents (fire or explosion), repairing and strengthening of existing concrete structures has become more common during the last decade due to the increasing knowledge and confidence in the use of composite advanced repairing materials. The past experience from real fires shows that it is exceptional for a concrete building to collapse as a result of fire and most fire-damaged concrete structures can be repaired economically rather than completely replacing or demolishing them. In this connection an experimental study was conducted to investigate the effectiveness of fibre reinforced polymer jackets for axial compressive and seismic shear performance of post-heated columns. This study also investigates the effectiveness of ferrocement laminate for the repairing of post-heated reinforced concrete columns.A total of thirty-five reinforced concrete columns were constructed and then tested after categorising them into three main groups: un-heated, post-heated and post-heated repaired. The post-heated columns were initially damaged by heating (to a uniform temperature of 500°C). The concrete cubes were also heated to various temperatures to develop the relation between compressive strength and ultrasonic pulse velocity. The residual compressive strength of the concrete cubes and reinforced concrete columns were determined by ultrasonic testing. The post-heated columns were subsequently repaired with unidirectional glass or carbon fibre reinforced polymer and ferrocement jackets. The experimental programme was divided into two parts. The columns of experimental part-1 were tested under axial compressive loading. The columns of experimental part-2 with a shear span to depth ratio of 2.5 were tested under constant axial and reversed lateral cyclic loading. The results indicated that the trend of reduction in ultrasonic pulse velocity values and in residual compressive strength of concrete was similar with increasing temperature. The reduction in residual stiffness of both post-heated square and circular columns was greater than the reduction in ultimate load. The circular sections benefited more compared to the square cross-sections with fibre reinforced polymers for improving the performance of post-heated columns in terms of compressive strength and ductility tested under axial compression. GFRP and CFRP jackets performed in an excellent way for increasing the shear capacity, lateral strength, ductility, energy dissipation and slowed the rate of strength and stiffness degradation of fire damaged reinforced concrete square and circular columns tested under combined constant axial and reversed lateral cycle loading. However, the effect of a single layer of glass or carbon fibre reinforced polymer on the axial stiffness of post-heated square and circular columns was negligible. The use of a ferrocement jacket for the repairing of post-heated square and circular columns enhanced the axial stiffness and ultimate load carrying capacity of columns significantly.

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Salunke, Pravahan Shamkant. "High Purity Magnesium Coatings and Single Crystals for Biomedical Applications." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin150488269765649.

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Jedidi, Mohamed Yassine. "Vers une meilleure prédiction des limites de formabilité des matériaux polycristallins à structure hexagonale." Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAE029.

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Cette thèse a pour objectif d’étudier la ductilité des matériaux à structure cristallographique hexagonale qui sont couramment utilisés dans différents secteurs de l’industrie, telles que les industries aéronautique et aérospatiale. Après compréhension de la physique des différents mécanismes de plasticité, tels que le glissement et le maclage, plusieurs modèles de comportement sont identifiés et enrichis pour décrire d’une manière pertinente le comportement mécanique des matériaux à structure hexagonale, à savoir l’alliage de titane et l’alliage de magnésium. Ces modèles sont intégrés numériquement en développant des schémas numériques assurant à la fois la robustesse et la fiabilité de l’intégration temporelle. Ils sont ensuite couplés aux critères d’instabilités plastiques suivants : bifurcation générale, imperfection initiale de Marciniak-Kuczynski, bifurcation de Rice et critère par perturbation linéaire. L’effet de plusieurs phénomènes et paramètres mécaniques sur la prédiction de la ductilité est particulièrement analysé. Les résultats numériques, en termes de limites de formabilité, sont comparés avec des résultats expérimentaux. Après leurs validations, les différents outils numériques développés dans le cadre de cette thèse peuvent être utilisés comme outil d’aide à l'optimisation des procédés de mise en forme des matériaux à structure hexagonale
The aim of this thesis is to study the ductility of hexagonal close packed (HCP) materials, which are being increasingly used in a wide range of engineering applications (aircraft and aerospace industries). After the step of the understanding of the physical phenomena and the different mechanisms that contribute to the plastic deformation (plastic slip, twinning…), a set of constitutive frameworks are selected from the literature and improved. These different frameworks are numerically integrated by implementing numerical schemes ensuring the accuracy and the robustness of the time integration. The adopted models are then coupled with several plastic instability criteria: general bifurcation, initial imperfection approach of Marciniak-Kuczynski, Rice bifurcation theory, and linear perturbation method. The effect of some phenomena and mechanical parameters on the predicted ductility limits are particularly studied. The results obtained by phenomenological models are compared to various experimental results. Once fully developed, assessed and validated, the numerical tools based on the above-described modeling can be advantageously used to help in the optimization of mechanical properties (crystallographic texture…) in order to improve the formability of HCP materials

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19

Laarich, Abdellatif. "Designing a Heat Treatment to Achieve Ductile Advanced High Strength Steels." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79754.

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Heat treatment is a way to significantly change materials properties. When presented with materials that lack certain mechanical properties, it is possible to change its chemical properties and microstructures by applying heat. This can help achieve better yield strength, ductility and toughness. This project discusses the effects of multiple distinct heat treatment methods for several materials in order to improve ductility and elongation without diminishing strength. The materials in question are High Aluminum Steel and Strenx 700MC steel, the first being under development and the second being a commercially available steel. These steels show promise to be used as high ductility, high strength, and 3rd generation steels. The heat treatments can change the mechanical proprieties of the base materials in order to optimize these steels for applications in vertical access solutions. The heat treatments in this project were Quenching and Partitioning (QP), Quenching and Tempering (QT), Austempering (AUST), Intercritical Heat Treatment (IHT) and other usual heat treatments such as Double normalizing (D-Norm). First, the most beneficial type of the above mentioned heat treatments was selected for each steel and series of heat treatments were performed in order to identify and optimize the best method for each steel. Then, heat treated samples underwent a series of tests to numerically quantify their properties and compare them to the existing steels in Alimak’s applications. The results show that Quenching and Partitioning is the most promising heat treatment for optimizing strength and ductility in High Aluminum Steel, with elongation values up to 19% together with yield strengths of 700 MPa. For Strenx 700MC a combination of temperature and time was found that gave an elongation of above 25% with a yield strength of 450 MPa. The explanation for the good properties was partly grain refinement and phase transformations during heat treatments.

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20

Calvo, Muñoz Jessica. "Efecto de los elementos residuales e impurezas en la ductilidad y mecanismos de fragilización en caliente de un acero de construcción 0.23C-0.9Mn-0.13SI." Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6048.

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El agrietamiento transversal en la superficie de los productos de colada continua es un problema que sigue provocando el rechazo de algunos de estos productos con las correspondientes pérdidas energéticas y económicas. A pesar de que el problema se ha conseguido minimizar para algunas calidades de acero, el reciclaje de chatarra, práctica cada vez más frecuente por sus beneficios económicos y medioambientales, está incorporando nuevos retos, especialmente en lo que se refiere a la aparición de grietas superficiales. El origen del agrietamiento para estos aceros se relaciona con el aumento en elementos residuales e impurezas que se introducen durante el reciclaje y son difíciles de eliminar.

Para conocer la influencia de estos elementos residuales e impurezas en el agrietamiento transversal, se evaluó la ductilidad en caliente de un acero de construcción 0.23C-0.9Mn-0.13Si con Cu y Sn como residuales y alto S. La ductilidad en caliente fue evaluada a partir de la reducción del área (%RA) de probetas ensayadas a tracción a temperaturas entre 650ºC y 1100ºC. La velocidad de deformación elegida para los ensayos fue 5·10-3s-1. Estas condiciones están en el intervalo de las que se dan durante el desdoblado, etapa crítica para la aparición de grietas. Las curvas de %RA en función de la temperatura se completaron con el estudio fractográfico y metalográfico de las probetas.

Durante los ensayos se varió la temperatura de austenización mediante recalentamientos a 1100ºC y a 1330ºC. Otra serie de ensayo consistió en la fusión y solidificación in-situ de las probetas. Además, se trabajó con el material en dos condiciones iniciales: colada (probetas extraídas de una palanquilla) y laminada (probetas extraídas de varilla corrugada). Un acero con una composición base similar pero sin elementos residuales fue evaluado con fines comparativos.

Las curvas de ductilidad en caliente fueron muy parecidas independientemente de la temperatura de recalentamiento, sin embargo, cuando el acero se ensayó en su condición laminada el valle de ductilidad obtenido fue más estrecho. Por otro lado, los mecanismos de fragilización variaron con la temperatura de recalentamiento y no con la condición inicial del material. Las fracturas tras recalentamientos a 1100ºC fueron interdendríticas y se relacionaron con las microsegregaciones de solidificación. Recalentamientos a 1330ºC originaron fracturas interganulares.

Las inclusiones de MnS, así como las segregaciones de S parecen tener un papel importante en este comportamiento. El efecto del S sólo puede ser evaluado adecuadamente cuando las probetas se solidifican in-situ para poner en solución el S que se encontrara formando MnS. Los resultados obtenidos mediante estas condiciones experimentales presentaron pozos de ductilidad más anchos que los obtenidos en condiciones de recalentamiento. Por otro lado, las fractografías muestran la gran tendencia al "hot shortness" que tiene el acero. Éste mecanismo de fragilización que actúa a muy altas temperaturas estaría debilitando los espacios interdendríticos a menores temperaturas.

Al comparar el comportamiento del acero industrial con el del acero limpio, lo primero que se ve es que el pozo de ductilidad es significativamente más estrecho para éste último. Así, el único mecanismo de fragilización identificado consiste en la concentración de la deformación en una fina capa de ferrita que se forma rodeando la austenita a temperaturas entre Ae3 y Ar3.

El cálculo de las microsegregaciones de solidificación indica que los elementos con más tendencia a enriquecer el último líquido en solidificar son el P y el S. Éste último además parece el responsable de la fragilidad del acero cuando se ensaya en condiciones de recalentamiento, tal y como se pudo determinar por espectroscopía Auger. A pesar de que no se ha podido demostrar, en Sn podría tener también un papel importante en las segregaciones intergranulares.
Transverse cracking in the surface is a problem related to the continuous casting steelmaking route. Its incidence has been minimized for several steel grades, but it is very sensitive to operational or compositional variations. In particular, the production of steel from scrap, which has great economic and environmental advantages, has introduced new challenges. The high incidence of transverse cracking for these steel grades is related to their high contents on residual elements which are introduced during the recycling and are difficult to eliminate.

The influence of residual elements and impurities on the transverse cracking susceptibility has been studied for a structural steel 0.23C-0.9Mn-0.13Si with high Cu and Sn as residuals, as well as high S. The evaluation was done by means of hot tensile tests. The reduction area (%RA) of the samples tested to fracture was taken as a measure of the hot ductility, and therefore, of the sensitivity of the steel to present transverse cracking. The analysis of the fracture surfaces and metallographies of the samples allowed the identification of the different embrittling mechanisms that could take place depending on the thermomechanical conditions.

During the tests, samples were first reheated to 1100ºC or 1330ºC, or in- situ melted. Then, they were tested at temperatures ranging from 650ºC to 1100ºC. The strain rate was 5×10-3s-1, close to the ones that take place during the unbending operation in continuous casting. The steel was tested for two initial conditions of the material: the as-cast (samples were machined from a billet), and the as-rolled (samples were machined from a corrugated bar). Moreover, another steel residual free was evaluated for comparison purposes.

The hot ductility curves (%RA vs. Temperature) were similar after different reheating treatments, but ductility troughs appeared narrower when the steel was tested in the as-rolled condition. However, fracture surfaces showed different features depending on the reheating temperature. On one side, the reheating treatment at 1100˚C promoted a mixture of intergranular and interdendritic brittle fracture. The interdendritic component of the fracture was related to microsegregations taking place during the solidification of the steel. On the other side, brittle samples tested after a reheating treatment at 1330˚C showed completely intergranular features.

MnS inclusions, as well as S segregations, seemed to have a very important role in the hot ductility behaviour of the steel. Since S forms particles with high melting points, samples had to be cast in-situ in order to put all S back into solution and then evaluate its effect on the hot ductility. For samples cast in-situ, the ductility troughs are wider than the ones obtained for reheated samples. Moreover, the fractographies of in-situ melted samples showed the high tendency of the steel to embrittle through "hot shortness". This mechanism that would act at very high temperatures could also be the responsible of the brittle behaviour of the steels at testing temperatures.

The ductility troughs for the clean steel were significantly narrower than the ones for the industrial steel at any testing condition. The only embrittling mechanism identified for the clean steel was the concentration of the deformations at a ferrite layer formed surrounding the austenite grains at temperatures between Ae3 and Ar3.

The composition of the last solidifying liquid was calculated according to microsegregation models. The calculations showed that P and S are the elements with the highest tendency to microsegregate and thus, the last solidifying liquid is enriched in these elements. By means of Auger spectroscopy the S was proved to be the embrittling element under reheating conditions. Though it could not be verified, special attention should be paid to Sn due to its tendency to segregate intergranularly.

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21

Luskin, Timothy Clark. "Investigation of Weldability in High-Cr Ni-base Filler Metals." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366210427.

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22

Palanivel, Sivanesh. "Thermomechanical Processing, Additive Manufacturing and Alloy Design of High Strength Mg Alloys." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849628/.

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The recent emphasis on magnesium alloys can be appreciated by following the research push from several agencies, universities and editorial efforts. With a density equal to two-thirds of Al and one-thirds of steel, Mg provides the best opportunity for lightweighting of metallic components. However, one key bottleneck restricting its insertion into industrial applications is low strength values. In this respect, Mg-Y-Nd alloys have been promising due to their ability to form strengthening precipitates on the prismatic plane. However, if the strength is compared to Al alloys, these alloys are not attractive. The primary reason for low structural performance in Mg is related to low alloying and microstructural efficiency. In this dissertation, these terminologies are discussed in detail. A simple calculation showed that the microstructural efficiency in Mg-4Y-3Nd alloy is 30% of its maximum potential. Guided by the definitions of alloying and microstructural efficiency, the two prime objectives of this thesis were to: (i) to use thermomechanical processing routes to tailor the microstructure and achieve high strength in an Mg-4Y-3Nd alloy, and (ii) optimize the alloy chemistry of the Mg-rare earth alloy and design a novel rare—earth free Mg alloy by Calphad approach to achieve a strength of 500 MPa. Experimental, theoretical and computational approaches have been used to establish the process-structure-property relationships in an Mg-4Y-3Nd alloy. For example, increase in strength was observed after post aging of the friction stir processed/additive manufactured microstructure. This was attributed to the dissolution of Mg2Y particles which increased the alloying and microstructural efficiency. Further quantification by numerical modeling showed that the effective diffusivity during friction stir processing and friction stir welding is 60 times faster than in the absence of concurrent deformation leading to the dissolution of thermally stable particles. In addition, the investigation on the interaction between dislocations and strengthening precipitate revealed that, specific defects like the I1 fault aid in the accelerated precipitation of the strengthening precipitate in an Mg-4Y-3Nd alloy. Also, the effect of external field (ultrasonic waves) was studied in detail and showed accelerated age hardening response in Mg-4Y-3Nd alloy by a factor of 24. As the bottleneck of low strength is addressed, the answers to the following questions are discussed in this dissertation: What are the fundamental micro-mechanisms governing second phase evolution in an Mg-4Y-3Nd alloy? What is the mechanical response of different microstructural states obtained by hot rolling, friction stir processing and friction stir additive manufacturing? Is defect engineering critical to achieve high strength Mg alloys? Can application of an external field influence the age hardening response in an Mg-4Y-3Nd alloy? Can a combination of innovative processing for tailoring microstructures and computational alloy design lead to new and effective paths for application of magnesium alloys?

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23

Gomes, Affonseca Netto Nelson. "The Effect of Friction Stir Processing on The Microstructure and Tensile Behavior of Aluminum Alloys." UNF Digital Commons, 2018. https://digitalcommons.unf.edu/etd/790.

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Friction Stir Processing (FSP) is a promising thermomechanical technique that is used to modify the microstructure of metals locally, and thereby locally improve mechanical properties of the material. FSP uses a simple and inexpensive tool, and has been shown to eliminate pores and also reduce the sizes of intermetallics in aluminum alloys. This is of great interest for research on solidification, production and performance of aluminum alloy castings because FSP can enhance the structural quality of aluminum casting significantly by minimizing the effect of those structural defects. In the literature, there is evidence that the effectiveness of FSP can change with tool wear of the tool used. Therefore, a study was first conducted to determine the effect of FSP time on the tool life and wear in 6061-T6 extrusions. Results showed the presence of two distinct phases in the tool life and wear. Metallographic analyses confirmed that wear in Phase I was due to fracture of the threads of the tool and Phase II was due to regular wear, mostly without fracture. Moreover, built-up layers of aluminum were observed between threads. The microhardness profile was found to be different from those reported in the literature for 6061-T6, with Vickers hardness increasing continuously from the the stir zone to the base material. To investigate the degree of effectiveness of FSP in improving the structural quality of cast A356 alloys, ingots with different quality (high and low) were friction strir processed with single and multiple passes. Analysis of tensile test results and work hardening characteristics showed that for the high quality ingot, a single pass was sufficient to eliminate the structural defects. Subsequent FSP passes had no effect on the work hardening characteristics. In contrast, tensile results and work hardening characteristics improved with every pass for the low quality ingot, indicating that the effectiveness of FSP was dependent on the initial quality of the metal. The evolution of microstructure, specifically the size and spacing of Silicon (Si) eutectic particles, was investigated after friction stir processing of high quality A356 castings with single and multiple passes. Si particles were found to coarsen with each pass, which was in contrast with previous findings in the literature. The nearest neighbor distance of Si particles also increased with each FSP pass, indicating that microstructure became progressively more homogeneous after each pass. In the literature, the improvement observed after FSP of Al-Si cast alloys was attributed to the refinement of Si particles. Tensile data from high quality A356 ingot showed that there was no correlation between the size of Si particles and ductility. To the author’s knowledge, this is the first time that the absence of a correlation between Si particle size and ductility has been found.

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24

Zhang, Jin. "Shakedown of porous materials." Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1I044/document.

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Cette thèse est consacrée à la détermination des états limites de l'adaptation des matériaux ductiles poreux sur la base du théorème de Melan et en considérant le modèle de la sphère creuse. Dans un premier temps, nous proposons le critère analytique macroscopique d'adaptation avec la matrice de von Mises sous deux charges particuliers, alterné et pulsé. Le critère analytique dépend des première et seconde invariants des contraintes macroscopiques, du signe du troisième et du coefficient de Poisson. Ensuite, ce critère est étendu aux charges cycliques répétées générales par la construction d'un champ de contraintes résiduelles d'essai plus approprié permettant simultanément des calculs analytiques et l'amélioration du modèle précédent. De plus, il est également utilisé pour les matériaux ductiles poreux avec une matrice de Drucker-Prager.L'idée repose d'abord sur la solution exacte pour le charge purement hydrostatique. Il s'avère que la ruine se produit par fatigue. Ensuite, des champs de contrainte d'essai appropriés sont construits avec des termes supplémentaires pour capter les effets de cisaillement. Le domaine de sécurité, défini par l'intersection du domaine d'adaptationet celui d'analyse limite (la ruine survenant brusquement par formation d'un mécanisme au premier cycle), est entièrement comparé avec des simulations élasto-plastique incrémentales et des calculs directs simplifiés.Enfin, nous fournissons une méthode numérique directe pour prédire le domaine de sécurité de l'adaptation des matériaux poreux soumis à des charges variant de manière indépendante en considérant le chemin critique du domaine de chargement au lieu de l'histoire entière. Le problème de l'adaptation est transformé en un problème d'optimisation de grande taille, qui peut être résolu efficacement par l'optimiseur non-linéaire IPOPT pour donner non seulement le facteur de charge limite, mais aussi le champ de contrainte résiduelle correspondant à l'état d'adaptation
This thesis is devoted to the determination of shakedown limit states of porous ductile materials based on Melan's static theorem by considering the hollow sphere model, analytically and numerically. First of all, we determine the analytical macroscopic shakedown criterion of the considered unit cell with von Mises matrix under alternating and pulsating special loading cases. The proposed macroscopic analytical criterion depends on the first and second macroscopic stresses invariants, the sign of the third one and Poisson's ratio. Then, the procedure is extended to the general cyclically repeated loads by the construction of a more appropriate trial residual stress field allowing analytical computations and the improvement of the previous model simultaneously. Moreover, this approach is applied to porous materials with dilatant Drucker-Prager matrix.The idea relies firstly on the exact solution for the pure hydrostatic loading condition. It turns out that the collapse occurs by fatigue. Next, suitable trial stress fields are built with additional terms to capture the shear effects. The safety domain, defined by the intersection of the shakedown limit domain and the limit analysis domain corresponding to the sudden collapse by development of a mechanism at the first cycle, is fully compared with step-by-step incremental elastic-plastic simulations and simplified direct computations. At last, we provide a direct numerical method to predict the shakedown safety domain of porous materials subjected to multi-varying independent loadings by considering the critical loading path of the load domain instead of the whole history. The shakedown problem is transformed into a large-size optimization problem, which can be solved efficiently by the non-linear optimizer IPOPT to give out not only the limit load factor, but also the corresponding residual stress field for the shakedown state

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25

King, Jason. "Energy Release Management Through Manipulated Geometries of Surgical Devices." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1342730044.

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Valio, Gustavo Trindade. "Modificação microestrutural da liga de magnésio AZ31 por fricção e mistura a altas velocidades." Universidade Federal de São Carlos, 2015. https://repositorio.ufscar.br/handle/ufscar/7477.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Due to the current growth in the fossil fuels consumption, there is a great concern about the increase in pollutant emissions. In order to reduce these emissions, research indicates that the decrease in vehicle weight can be one of the solutions to reduce these gas emissions. One possible way to reduce the car weight is the replacement of parts that uses high density metals by Magnesium alloys. The major problem with this replacement is the lack of ductility that this material has at room temperature, being necessary to heat the plates before the conformation. This heating process has a high production costs and it is unfeasible to use in the automotive industry today. In view of this problem, this work aims to study this lack of conformity to room temperature using a microstructure modification technique located in the regions of conformation. The technic used was Friction Stir Processing (FSP) at high speed. This processing is similar to Friction Stir Welding (FSW), but without joining materials. The FSP is just a localized microstructural modification. The analysis performed in this study after processing at 1, 7 and 10 m/min show that the microstructure and mechanical properties undergoes various changes at for every processing speed output different. The results showed that the material after processing improves the ductility at room temperature as grain size decreases.
Com o atual crescimento do consumo de combustíveis fosseis, existe uma grande preocupação com o aumento de emissões de gases poluente. Para redução dessas emissões, pesquisas apontam que a diminuição do peso de veículos pode ser uma das soluções para reduzir as emissões de gases poluentes pelo aumento da eficiência energética. Uma forma possível de diminuir o peso de automóveis é pela substituição de partes que utilizam metais com alta densidade por ligas de Magnésio. O grande problema desta substituição é a falta de dutilidade que este material possui a temperatura ambiente, sendo necessário aquecer as chapas antes da conformação. Atualmente este processo de aquecimento gera um alto custo de produção dificultando sua utilização na indústria automotiva. Tendo em vista este problema, o presente trabalho tem como objetivo entender esta dificuldade na conformação a temperatura ambiente e propor uma solução utilizando uma técnica de modificação microestrutural localizada nas regiões de conformação. Esta técnica é o Processamento por Fricção e Mistura (FSP – Friction Stir Processing) à altas velocidade. Este processamento é semelhante ao de Soldagem por Fricção e Mistura (FSW – Friction Stir Welding), mas sem a formação de uma região de união entre materiais. O FSP é apenas uma modificação microestrutural localizada. As análises realizadas neste estudo após o processamento à 1, 7 e 10m/min apontam que a microestrutura e as propriedades mecânicas sofrem variações diferentes a cada velocidade de processamento. Os resultados mostraram que o material obteve uma melhora na dutilidade à temperatura ambiente devido à diminuição do tamanho de grão.

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27

Perez-Barbante, Dezire Q'anna. "IN-PLANE CYCLIC SHEAR PERFORMANCE OF PIPE STEM REINFORCED COB WALL." DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2116.

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This thesis investigates full-scale pipe stem reinforced cob walls under in-plane cyclic shear loads. Cob is the combination of clay subsoils, sand, straw and water that is built in lifts to produce monolithic walls. There is insufficient amount of information on cob as a building material in today’s age. The prior research that exists has examined varying straw content and type, water content, and mixture ratios to determine their effect on strength. There is currently one report that analyzes full-scale cob walls under in-plane loading. This thesis looks to iterate the full-scale tests and specifically studies the effect of reinforcement on cob walls. Concurrent to this research, another thesis was written that investigates a full-scale wire mesh reinforced cob wall under in-plane cyclic shear loads. From the data collected, a shear failure was suggested for the stem pipe wall. There appeared to be a large amount of ductility from the data and the cracks formed. Ductility, a seismic response modification factor (R-Factor) and stiffness were calculated using the yield point and ultimate loads.Iterations of this research and those performed in the past can be helpful in integrating cob in to the California Building Code.

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28

Subramani, Manoj. "Dynamic response of porous ductile materials containing cylindrical voids." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0310.

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La rupture des matériaux ductiles résulte de l’interaction de trois mécanismes, à savoir la nucléation, la croissance et la coalescence des vides. Dans ce doctorat, nous nous intéressons à l’endommagement des matériaux poreux par croissance de vides cylindriques, sous chargement dynamique. Cette étude a un intérêt particulier notamment pour l’atténuation des ondes de choc dans le cadre de la protection des structures. Par ailleurs, du fait du développement de la fabrication additive, la conception de matériaux contenant des vides cylindriques est une voie possible pour créer des matériaux légers à haut pouvoir dissipatif. Ce travail s’attèle à décrire le comportement dynamique de matériaux architecturés tels que des nids d’abeille faiblement poreux. En conditions dynamiques, les vides sont soumis à une expansion rapide, induisant localement (au voisinage de la cavité) de très fortes accélérations. Cet effet d’inertie locale, ou micro-inertie, est connu pour influencer fortement la réponse macroscopique mais aussi le développement de la porosité. En fait, il a été montré précédemment que le tenseur des contraintes macroscopiques est la somme d’un tenseur des contraintes statiques (dans le sens indépendant de la micro inertie) et d’un tenseur des contraintes dynamiques. Ce dernier terme va contenir toutes les informations liées aux accélérations et sera intrinsèquement relié à la microstructure (taille et forme des vides). Dans ce travail, un volume élémentaire représentatif cylindrique est adopté (rayons interne a et externe b, hauteur 2l). Les contraintes statiques dérivent d’un modèle de la littérature. Les contraintes dynamiques sont évaluées à partir d’un champ cinématiquement admissible. On observe in fine que les contraintes dynamiques sont proportionnelles à la masse volumique de la matrice, sont liées à la porosité, au tenseur vitesse de déformation de manière quadratique, à sa dérivée temporelle de manière linéaire mais surtout fait intervenir deux longueurs internes (rayon interne du vide et longueur de celui-ci). Pour des chargements axisymétriques, on montre que les contraintes dynamiques dans le plan ne dépendent que du rayon du vide alors que les contraintes dynamiques hors plan font apparaître les deux longueurs internes. Les prédictions du modèle ont été testées en considérant de nombreux exemples parmi lesquels le chargement sphérique, en contraintes planes, déformations planes, traction uniaxiale, chargement biaxial. En déformation plane sous chargement axisymétrique, le modèle quasi-statique prédit que le tenseur des contraintes associé est sphérique. En chargement dynamique, en revanche la contrainte axiale est différente de la composante radiale. Nous avons aussi observé pour un chargement sphérique que l’accroissement de la porosité résulte d’une augmentation du rayon du vide et d’une diminution du rayon externe du VER. Cette observation est propre aux effets de micro-inertie. De nombreuses tendances originales sont illustrées dans ce document. A noter que l’ensemble des prédictions du modèle a été validé par confrontation avec des calculs éléments finis sur des cellules élémentaires cylindriques
The fracture of ductile materials is often the result of the nucleation, growth and coalescence of microscopic voids. In this thesis, we mainly focus on the dynamic void evolution in porous media containing cylindrical voids. This study covers a problem that is of particular interest in many areas of research (e.g. development of shock mitigation devices for civil or military applications). Owing to the development of additive manufacturing, the processing of porous material with cylindrical voids is an option to create lightweight materials having interesting properties in terms of energy dissipation. Therefore, our work aims at describing the dynamic response of architectured materials such as honeycomb structures. In dynamic loading, microvoids sustain an extremely rapid expansion which generates strong acceleration of particles in the vicinity of cavities. These micro-inertia eﬀects are known to play a significant role in the macroscopic response and the development of damage in porous media. In fact, the overall macroscopic stress is found to be the sum of two contributions: a static term (micro-inertia independent term) and a dynamic term (micro-inertia dependent term), the latter being related to the microstructure (e.g. size and aspect ratio of voids). In our work, a cylindrical shell is adopted as a Representative Volume Element (internal and external radii a and b, length 2l) for the porous material. The static term is derived from a yield function available in the literature. The dynamic stress is evaluated analytically using a trial velocity field for cylindrical voids combined with the multi-scale approach developed in the literature in LEM3. It is shown that the dynamic stress is scaled by the mass density, two characteristic lengths of the voids, the porosity, the macroscopic strain rate tensor and the time derivative of the strain rate tensor. An important outcome of the model is the diﬀerential lengthscale eﬀect which exists between in-plane and out of plane components of the macroscopic stress. Namely, it is observed for axisymmetric loading that in-plane dynamic stress components are only related to the void radius a while the out of plane stress component is linked to a and the length of the RVE, l. In the thesis, we present the dynamic response of the porous medium when subjected to various loading conditions: spherical loading, axisymmetric plane strain loading, uniaxial loading and biaxial loading. While for plane strain loading under quasi static condition, the overall axial stress is spherical, in dynamic conditions, the inertia contribution hinders the overall stress tensor from being spherical. Another important result of the proposed theory is the eﬀect of the void length, which does not exist in quasi static conditions where the overall response is solely modulated by the porosity. The case of thin cylinders under dynamic loading reveals a peculiar damage kinetics. In fact, the damage developed in such porous materials results from an increase of the void radius and a reduction of the external radius. The void collapse for uniaxial as well as for biaxial loadings are new observations. The analytical model predictions are validated based on comparisons with finite element calculations (Abaqus/Explicit)

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Cunha, Emerson Fernandes da. "Caracterização da resistência à deformação a quente do aço baixo carbono microligado ao vanádio." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2009. http://hdl.handle.net/10183/23923.

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Este trabalho, realizado em cooperação com a Gerdau Riograndense, tem por finalidade avaliar o comportamento do aço GG1013-M, um aço baixo teor de carbono microligado com vanádio e manganês, na laminação a quente no que tange a sua resistência à deformação, possibilitando assim a tomada de decisão em relação a modificações no processo. Foram realizados testes em simulador termomecânico Gleeble™ para determinação das temperaturas a serem usadas no teste prático no laminador, onde testou-se lotes que cobrissem toda a amplitude da faixa de composição química da qualidade do aço em estudo. No teste prático no laminador, foram retiradas amostras para os ensaios mecânicos, onde identificou-se, por intermédio do tratamento de dados em software estatístico, a influência da variação dentro da faixa da composição química sobre os limites de escoamento e resistência. Como resultado, conseguiu-se determinar a faixa de temperatura mais provável, onde a resistência a deformação a quente é menor, minimizando ou eliminando as conseqüências da redução de ductilidade a quente por conta do endurecimento da matriz por precipitação dos elementos de liga em forma de compostos.
This work was conducted in cooperation with Gerdau Riograndense aiming at the evaluation of the hot rolling behavior of a low carbon steel microalloyed with manganese and vanadium (internally GG1013-M steel).The deformation resistance was evaluated, allowing for the decision in relation to changes in the process. A thermomechanical simulator GleebleTM was used to determine the temperatures to be used in practical tests in the rolling mill, where it was tested different material batches covering the large range of chemical compositions for this kind of steel. Mechanical tests were performed on samples taken from the practical tests in the rolling mill. From this tests the influence of chemical composition variation on the yeld strength and maximum stress was studied. As a result, we were able to determine the most likely range of temperatures for a minimization of hot strentgh, therefore also minimizing or eliminating the consequences of the reduction in the hot ductility due precipitation hardening of the matrix.

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Hasan, Md Shahanur. "Erosive wear analysis of Mn-steels hammers due to coal impact in a high-speed pulverising mill." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/122874/1/Md%20Shahanur_Hasan_Thesis.pdf.

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This project aims to develop a finite element erosion wear model of high manganese steels to predict the erosive wear behavior due to coal impact. To obtain the material model parameters, the ductility, strain hardening effect and ability to withstand dynamic loading were investigated using tensile test and micrographic analysis. The finding of this thesis will benefit relevant industries to select the materials with high erosion wear resistance, thereby improving process economics of coal pulverization process.

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Edwards, Ylva. "Influence of waxes on bitumen and asphalt concrete mixture performance." Doctoral thesis, KTH, Väg- och banteknik, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-553.

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This doctoral thesis consists of a literature review, presented in two papers, and another six papers describing experimental studies of the influence of different kinds of wax and polyphosporic acid on bitumen and asphalt concrete mixture properties. The literature review should give an extensive description of the field of knowledge concerning wax in bitumen. Effects of wax in crude oil, bitumen and asphalt concrete as well as test methods for studying these effects are described. Theories behind possible mechanisms are also discussed, and commercial wax as additive to bitumen for different purposes included. The experimental parts comprise laboratory studies involving totally five 160/220 penetration base bitumens from different sources, two isolated bitumen waxes, five commercial waxes and one polyphosphoric acid. Asphalt concrete slabs, containing base or modified bitumen were prepared and tested. Binder properties were evaluated using different types of laboratory equipment, such as dynamic shear rheometer (DSR), bending beam rheometer (BBR), differential scanning calorimeter (DSC), force ductilometer, as well as equipment for determining conventional parameters like penetration, softening point, viscosity, and Fraass breaking point. Fourier Transform Infrared (FTIR) spectroscopy and Thin Layer Chromatography (TLC-FID) were used for chemical characterization. The binders were aged by means of the rolling thin film oven test (RTFOT) and pressure ageing vessel (PAV) in combination. Asphalt concrete properties were evaluated at low temperatures using the tensile strain restrained specimen test (TSRST) and creep test at -25°C. Dynamic creep testing was performed at 40°C, as well as complex modulus tests between 0 and 20°C. Binder test results indicated that the magnitude and type of effect on bitumen rheology depend on the bitumen itself, type of crystallizing fraction in the bitumen and/or type and amount of additive used. Bitumen composition was found to be of decisive importance. Adding polyethylene wax or polyphosphoric acid, especially to a non-waxy 160/220 penetration grade bitumen, showed no or positive effects on the rheological behaviour at low temperatures (decrease in stiffness) as well as medium and high temperatures (increase in complex modulus and decrease in phase angle). However, the corresponding positive effects could not be shown in dynamic creep testing (at 40°C) of asphalt concrete mixtures containing these modified binders. Adding FT-paraffin decreased the physical hardening index for all bitumens. Also polyethylene wax and montan wax showed this effect for some bitumens. Slack wax showed a large increasing effect on physical hardening, and polyphosphoric acid none or a minor negative effect. No correlation between physical hardening index (PHI) and wax content by DSC was found in this study, involving both natural bitumen wax and commercial wax. Addition of the commercial waxes used showed no or marginally positive influence on bitumen ageing properties for the bitumens and test conditions used. Comparing asphalt mixture test results to the corresponding binder test results, the effects on asphalt mixtures from adding commercial wax or polyphosphoric acid were less evident. Significant binder physical hardening by BBR could not be confirmed by TSRST.
QC 20101006

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Moreno, Rômulo Fernandes. "Estudo das variáveis que afetam a tenacidade e a ductilidade do aço PH13-8Mo utilizado na indústria aeronáutica." Universidade Federal de São Carlos, 2012. https://repositorio.ufscar.br/handle/ufscar/905.

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Made available in DSpace on 2016-06-02T19:12:30Z (GMT). No. of bitstreams: 1 5457.pdf: 7456737 bytes, checksum: 1d18f487e08219cebbd323e719bd80ff (MD5) Previous issue date: 2012-10-27
Precipitation Hardening Stainless Steel PH13-8Mo is a high strength steel used in the aerospace industry. Beyond the high strength, this grade has relatively high toughness and ductility for the strength achieved. The aerospace industry is increasingly asking for high strength materials with higher toughness and ductility than the actual limits required. Villares Metals, manufacturer of specialty steels and alloys, supplies the 13-8 steel (Villares grade N4534QA) for the aerospace industry like Embraer and ELEB (landing gear manufacturer of Embraer aircrafts). Although Villares 13-8 steel meets the international and the aerospace specifications, is characteristic of this company to improve its products and follow the new requirements of the customers and the market. Thus, is of its interest to produce the 13-8 steel with higher toughness and ductility. Therefore, the objective of this work is to study the variables which affect the 13-8 steel toughness and ductility aiming to produce it with improved properties. It were studied the effect of the alloying and residual elements, steelmaking process (remelting), hot forming process (forging and rolling) and heat treatment process. The verification of these effects was verified through tensile and impact Charpy V tests.
O aço inoxidável endurecível por precipitação PH13-8Mo (13-8) é um aço de elevada resistência mecânica utilizado na indústria aeronáutica. Além da elevada resistência mecânica, este aço possui ductilidade e tenacidade relativamente elevadas para o nível de resistência atingido. A indústria aeronáutica vem, cada vez mais, solicitando materiais de alta resistência mecânica com tenacidade e ductilidade mais elevadas em relação às solicitações atuais. A Villares Metals, usina siderúrgica produtora de aços e ligas especiais, é fornecedora do aço 13-8 (marca Villares N4534QA) para as indústrias do segmento aeronáutico, como Embraer e ELEB (fabricante dos trens de pouso dos aviões da Embraer). Apesar do aço 13-8 da Villares Metals atender as principais normas internacionais e do segmento aeronáutico, é prática desta empresa estar sempre buscando melhorar os seus produtos e acompanhar as novas solicitações dos clientes e do mercado. Sendo assim, é de seu interesse produzir o aço 13-8 com tenacidade e ductilidade mais elevadas. Portanto, o objetivo deste trabalho é estudar as variáveis que afetam a tenacidade e a ductilidade do aço 13-8 com o objetivo de se obtê-lo com estas propriedades otimizadas. Foram estudados os efeitos de elementos de liga, de elementos residuais, do processo de elaboração (refusão), dos processos de conformação a quente (forjamento e laminação) e do processo de tratamento térmico. A verificação desses efeitos foi realizada através de ensaios mecânicos de tração e de impacto Charpy V.

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Aljerf, M. "Propriété Mécaniques des Verres Métalliques ; Mise en Forme et Applications." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00565652.

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Ce travail de thèse considère les modes de déformations des verres métalliques produits sous différentes formes (verres massifs, rubans et particules). La déformation hétérogène dans des échantillons massifs de verres métalliques à base de zirconium est étudiée par microscopie électronique à balayage. Le dégagement rapide de l'énergie élastique stockée sous forme de chaleur lors de la déformation est responsable de la fusion locale observée dans les bandes de cisaillement. Le calcul du profil de température autour d'une bande par un modèle analytique est cohérent avec les observations morphologiques et les rapports d'apparition de nano-cristaux dans la zone déformée. La mise en forme par recuit des rubans de verres métalliques a été étudiée. L'étude aboutit à la mise en forme sans fragilisation des rubans appartenant à différentes compositions de systèmes d'alliages dit métal-métal et métal-métalloïde. Un processus de traitement thermique est suggéré pour assurer la redistribution des contraintes imposées avant l'intervention de la fragilité thermique. Un brevet industriel basé sur ces résultats a été conjointement déposé avec un grand fabriquant de montres mécaniques. De nouveaux matériaux composites d'alliages légers commerciaux à base de Mg et d'Al renforcés par des dispersions de particules de verres métalliques ont été réalisés sans porosité. Une amélioration très nette des propriétés mécaniques est obtenue.

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Gani, Léa. "Incorporation de chaînes longues dans des alliages nanostructurés de polymères semi-cristallins : extrusion réactive, structure et propriétés mécaniques." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://pastel.archives-ouvertes.fr/pastel-00557087.

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Des alliages nanostructurés, co-continus et thermodynamiquement stables sont synthétisés, par extrusion réactive d'un polyéthylène fonctionnalisé (FPE) et d'un mélange bimodal de petites et longues chaînes de polyamide 6 (PA). Les petites chaînes réagissent rapidement pour former beaucoup de copolymères, garantissant ainsi la nanostructuration. Le greffage et l'incorporation des longues chaînes a pour but d'introduire des enchevêtrements et des molécules liens entre les cristallites de PA. Deux extractions sélectives successives nous ont permis de caractériser les chaînes de copolymères greffés et les chaînes non-réagies de FPE et de PA. Les propriétés macroscopiques des alliages sont optimisées en jouant sur l'ordre d'introduction des constituants, les conditions d'extrusion et la composition de la phase de PA. L'étude structurale des alliages et des copolymères greffés précise l'organisation des chaînes dans les deux nanostructures. Les deux phases de FPE et PA cristallisent de manière confinée ce qui confère aux alliages des propriétés mécaniques remarquables. Aux faibles déformations et au dessus de la fusion du FPE, les alliages de composition 64/36 FPE/PA en masse, présentent une tenue thermomécanique d'une vingtaine de mégapascals. Les longues chaînes de PA jouent le rôle de chaînes liens entre les cristallites et améliorent la ductilité des alliages nanostructurés à haute température (allongement à la rupture 250% à 150°C). Des expériences de diffusion des rayons X couplées à de la microscopie électronique en transmission avant et après traction permettent de relier les évolutions structurales et morphologiques aux comportements mécaniques de ces alliages.

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Kahan, Michel. "Approches stochastiques pour le calcul des ponts aux séismes." Phd thesis, Ecole Nationale des Ponts et Chaussées, 1996. http://tel.archives-ouvertes.fr/tel-00529960.

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Nous proposons dans cette étude quelques méthodes stochastiques pour le calcul des ponts aux séismes. Après avoir rappelé les représentations du mouvement sismique par spectres de réponse, densités spectrales de puissance et signaux temporels, nous introduisons des modèles de variabilité spatiale d'ondes sismiques. Nous en étudions l'effet sur la réponse linéaire des ponts grâce à une méthode de spectre de réponse pour structures multi-supportées. Nous proposons une méthode simplifiée permettant un calcul rapide de la sensibilité des ouvrages à de faibles variations spatiales des mouvements du sol et nous donnons un algorithme efficace pour le calcul de la réponse la plus défavorable lorsque les variations spatiales sont grandes et incertaines. Pour tenir compte du potentiel de ductilité des ponts, nous proposons une méthode de spectre de réponse tirant partie de la localisation des non-linéarités matérielles dans la structure (rotules plastiques, appareils d'appui). Les éléments non-linéaires sont remplacés par des éléments linéaires équivalents. Une technique de synthèse modale adaptée à la localisation des non-linéarités permet un calcul rapide de la réponse. Cette approche intègre le caractère aléatoire des sollicitations sans avoir recours à de coûteuses simulations de Monte-Carlo. Elle donne de bons résultats en termes de demande de ductilité et d'énergie dissipée par cycles d'hystérésis dans les éléments non-linéaires. Enfin, nous évoquons une technique de calcul de fiabilité de structures non-linéaires sous sollicitations stochastiques.

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Karolak, Cyprien. "CarboFrac : Analyse et modélisation de l'engrenage (d'un siège auto) en acier à faible teneur en carbone carbonitruré." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM057/document.

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Ce travail vise à améliorer la compréhension et la modélisation de la rupture des matériaux métalliques à gradient de propriétés. L'application se fait sur des pignons en acier 20MnB5 carbonitrurés insérés dans un "recliner", mécanisme de sécurité des siègesautomobiles. Le traitement de carbonitruration consisteà enrichir en carbone et azote une couche externe despièces en les chauffant dans le domaine austénitiquedans une atmosphère riche en ces deux éléments. Puisles pièces sont trempées afin de déclencher unetransformation martensitique. On obtient ainsi unmatériau à gradient de propriétés, intéressant pour despièces de transmission de puissance comme lesengrenages. Ce projet a commencé par l’analyse de larupture de mécanismes de sièges en test industriel. Celaa confirmé le double comportement à rupture binaire dumatériau : fragile sur une couche externe, ductile àl’intérieur. Un banc d’essai, spécialement conçu pour ceprojet, soumet une dent à un effort latéral jusqu’àrupture complète. Des observations in situ sonteffectuées et la courbe force-déplacement estenregistrée, montrant la diversité de comportement enfonction de la profondeur d'engagement des dents et dela présence ou non de la couche carbonitrurée. Desessais de traction, de flexion 4 points et de cisaillementsur éprouvettes papillons sont utilisés pour mesurer lespropriétés plastiques et calibrer les critères de rupturede la couche carbonitrurée comme de l'acier de base. Laplasticité de Von Mises avec une loi d'écrouissagesimple rend très bien compte de tous ces essaismécaniques. Différents critères de rupture ductile issusde la littérature sont calibrés; ils ne parviennent pas àreprésenter correctement tous les essais réalisés.Un critère plus adapté est donc proposé enconclusion de cette campagne expérimentale. Lasimulation de la rupture dans LS-Dyna est réaliséeavec une technique d'érosion d'éléments dont leslimitations sont discutées. La comparaison avec larupture de dent expérimentale permet d'évaluer lescritères numériques identifiés et d'analyser leslimites actuelles de la simulation, en particulier lanécessité de prendre en compte plus finement àl'avenir le gradient de propriétés mécaniques ainsique les contraintes résiduelles de compression dela couche carbonitrurée
This work aims at a better understanding and modeling of the failure of gradient metallic materials. It is applied to carbonitrided pinions made out of 20MnB5 steel, inserted in a "recliner", a safety mechanism of automotive seats. Carbonitriding induces high surface hardness while preserving significant core ductility. The experimental analysis of the fracture behavior of seat recliners in an industrial test confirmed the dual failure behavior of the component : brittle external layer, ductile core material. A test bench has been specifically designed for the project: one tooth is submitted to a lateral force until complete failure. In situ observations are performed and the load-displacement curve recorded, showing a variety of behaviors as a function of the teeth engagement depth and of the presence or not of the carbonitrided layer. Experimental tests with various tress states were conducted to measure plastic properties as well as to calibrate fracture criteria, for the carbonitrided layer and for the core steel. Von Mises plasticity and a simple strain hardening curve fit very well all these experiments. As fracture criteria from the literature were unable to predict failure correctly for all the mechanical tests, an adapted criterion has therefore been proposed as an outcome of this extensive mechanical testing campaign. Fracture simulation in LS Dyna has been performed using the element erosion technique, the limitations of which are discussed. Comparison with the experimental tooth fracture measurements allows evaluation of the proposed failure criteria, and enables to stress out and discuss the present limits of the simulation, concluding that it will be necessary in future work to account more finely for the mechanical property gradient together with the compressive residual stresses in the carbonitrided layer

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Noecker, Fredrick F. II. "Metallurgical investigation into ductility dip cracking in nickel based alloys." 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3285743.

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(7041476), Mohamadrusydi B. Mohamadyasin. "DEVELOPMENT OF HIGH DUCTILITY ALUMINUM ALLOYS FOR DIE CASTING." Thesis, 2019.

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Aluminum-Silicon (Al-Si) alloys are often preferred in the die casting industry due to excellent castability, high strength, corrosion resistance and low cost. Commonly, iron (Fe) is alloyed with the alloys to prevent die soldering. However, the addition of Fe in most of Al-Si alloys leads to formation of the intermetallic β-AlFeSi. The β-AlFeSi is harmful to the alloy structural integrity due to its needle-like morphology that creates stress concentration at the microscopic level. The phase presence is unfavorable to the mechanical properties and significantly reduces the elongation of the alloys. This research attempted to find viable way to control the morphology and formation of the β-AlFeSi phase.

Thermodynamic simulations were done to investigate the sequence of intermetallic formation and other phases at different alloy compositions. The analysis of solidification paths of different alloys provided the correlation between the phase formation sequence and the fraction of the β-AlFeSi phase. The analysis also identified the feasible region of alloy design for minimizing the β-AlFeSi formation. Based on the thermodynamics simulation analysis, five alloys of different compositions were designed to validate the finding of the simulation.

The tensile test results of the alloys indicated that lowering the Fe content increases the elongation of the alloy. The results also showed that elongation was reduced with the increase of Si level due to the formation of eutectic Silicon. The change of both Fe and Mn did not significantly affect the mechanical property of the alloy when the ratio of Fe to Mn was constant. Microscopic analysis showed that lowering the Fe level had effectively altered the morphology of the β-AlFeSi needle like structure. The β-AlFeSi was found to be smaller in terms of size when Fe is lower, subsequently reducing the probability of β-AlFeSi phase to be stress riser and crack initiation.

The influence of heat treatment to the mechanical property of the alloys was also studied. The mechanical result on the heat-treated samples indicated that heat treatment is a viable method to improve the elongation property of the alloy. Microscopic observations showed that the β-AlFeSi phase was broken into shorter structures over the solution heat treatment process, resulting in better elongation.

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Glanton, Darryl Britt. "Correlating Grain Boundary Microstructure and Ductility Loss on Aging in Haynes® 25." 2007. http://etd.utk.edu/2007/GlantonDarryl.pdf.

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Chandra, Shekhar P. "Development of wrought Mg-Li based alloys with improved strength and ductility." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5358.

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A comprehensive investigation has been undertaken to develop cold rolled Mg-Li based alloys with tensile properties superior to the existing commercial or experimental Mg-Li based alloys. In this endeavor, melting and casting of these alloys proved to be very challenging. In the present work, the challenges encountered in melting and casting of these alloys and efforts to successfully overcome them to produce good quality castings, which could be easily cold rolled to achieve tensile properties hitherto not achieved for Mg-Li based alloys are discussed. Overall, it can be said that the squeeze cast LZ82 alloy exhibited superior tensile properties compared to LZ81 alloy for all the processing routes investigated in the present work. The best tensile properties were obtained for 85% cold rolled LZ82 alloy, i.e., 219 MPa 0.2% proof stress, 262 MPa ultimate tensile strength and 64% elongation to failure, which are superior to any commercial or experimental Mg-Li based alloy

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Brooks, Iain. "Synthesis and Mechanical Properties of Bulk Quantities of Electrodeposited Nanocrystalline Materials." Thesis, 2012. http://hdl.handle.net/1807/32670.

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Nanocrystalline materials have generated immense scientific interest, primarily due to observations of significantly enhanced strength and hardness resulting from Hall-Petch grain size strengthening into the nano-regime. Unfortunately, however, most previous studies have been unable to present material strength measurements using established tensile tests because the most commonly accepted tensile test protocols call for specimen geometries that exceeded the capabilities of most nanocrystalline material synthesis processes. This has led to the development of non-standard mechanical test methodologies for the evaluation of miniature specimens, and/or the persistent use of hardness indentation as a proxy for tensile testing. This study explored why such alternative approaches can be misleading and revealed how reliable tensile ductility measurements and material strength information from hardness indentation may be obtained. To do so, an electrodeposition-based synthesis method to produce artifact-reduced specimens large enough for testing in accordance with ASTM E8 was developed. A large number of 161 samples were produced, tested, and the resultant data evaluated using Weibull statistical analysis. It was found that the impact of electroforming process control on both the absolute value and variability of achievable tensile elongation was strong. Tensile necking was found to obey similar processing quality and geometrical dependencies as in conventional engineering metals. However, unlike conventional engineering metals, intrinsic ductility (as measured by maximum uniform plastic strain) was unexpectedly observed to be independent of microstructure over the grain size range 10-80nm. This indicated that the underlying physical processes of grain boundary-mediated damage development are strain-oriented phenomena that can be best defined by a critical plastic strain regardless of the strength of the material as a whole. It was further shown that the HV = 3•σUTS expression is a reliable predictor of the relationship between hardness and strength for electrodeposited nanocrystalline materials, provided the material is ductile enough to sustain tensile deformation until the onset of necking instability. The widely used relationship HV = 3•σY was found to be inapplicable to this class of materials owing to the fact that they do not deform in an “ideally plastic” manner and instead exhibit plastic deformation that is characteristic of strain hardening behaviour.

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42

Basu, Sumit. "Numerical Simulation Of Fracture Initiation In Ductile Solids Under Mode I Dynamic Loading." Thesis, 1999. https://etd.iisc.ac.in/handle/2005/1520.

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43

Basu, Sumit. "Numerical Simulation Of Fracture Initiation In Ductile Solids Under Mode I Dynamic Loading." Thesis, 1999. http://etd.iisc.ernet.in/handle/2005/1520.

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44

"Properties of Cerium Containing Lead Free Solder." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.15802.

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abstract: With increasing concerns of the intrinsic toxicity of lead (Pb) in electronics, a series of tin (Sn) based alloys involving silver (Ag) and copper (Cu) have been proposed as replacements for Pb-Sn solder and widely accepted by industry. However, they have a higher melting point and often exhibit poorer damage tolerance than Pb-Sn alloys. Recently, a new class of alloys with trace amount of rare-earth (RE) elements has been discovered and investigated. In previous work from Prof. Chawla's group, it has been shown that cerium (Ce)-based Pb-free solder are less prone to oxidation and Sn whiskering, and exhibit desirable attributes of microstructural refinement and enhanced ductility relative to lanthanum (La)-based Sn-3.9Ag-0.7Cu (SAC) alloy. Although the formation of RESn3 was believed to be directly responsible for the enhanced ductility in RE-containing SAC solder by allowing microscopic voids to nucleate throughout the solder volume, this cavitation-based mechanism needs to be validated experimentally and numerically. Additionally, since the previous study has exhibited the realistic feasibility of Ce-based SAC lead-free solder alloy as a replacement to conventional SAC alloys, in this study, the proposed objective focuses on the in in-depth understanding of mechanism of enhanced ductility in Ce-based SAC alloy and possible issues associated with integration of this new class of solder into electronic industry, including: (a) study of long-term thermal and mechanical stability on industrial metallization, (b) examine the role of solder volume and wetting behavior of the new solder, relative to Sn-3.9Ag-0.7Cu alloys, (c) conduct experiments of new solder alloys in the form of mechanical shock and electromigration. The research of this new class alloys will be conducted in industrially relevant conditions, and the results would serve as the first step toward integration of these new, next generation solders into the industry.
Dissertation/Thesis
Ph.D. Materials Science and Engineering 2012

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45

Patel, Vipulkumar Ishvarbhai. "Nonlinear inelastic analysis of concrete-filled steel tubular slender beam-columns." Thesis, 2013. https://vuir.vu.edu.au/22015/.

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High strength thin-walled concrete-filled steel tubular (CFST) slender beam-columns may undergo local and global buckling when subjected to biaxial loads, preloads or cyclic loading. The local buckling effects of steel tube walls under stress gradients have not been considered in existing numerical models for CFST slender beam-columns. This thesis presents a systematic development of new numerical models for the nonlinear inelastic analysis of thin-walled rectangular and circular CFST slender beam-columns incorporating the effects of local buckling, concrete confinement, geometric imperfections, preloads, high strength materials, second order and cyclic behavior. In the proposed numerical models, the inelastic behavior of column cross-sections is simulated using the accurate fiber element method. Accurate constitutive laws for confined concrete are implemented in the models. The effects of progressive local buckling are taken into account in the models by using effective width formulas. Axial load-moment-curvature relationships computed from the fiber analysis of sections are used in the column stability analysis to determine equilibrium states. Deflections caused by preloads on the steel tubes arising from the construction of upper floors are included in the analysis of CFST slender columns. Efficient computational algorithms based on the Müller’s method are developed to obtain nonlinear solutions. Analysis procedures are proposed for predicting load-deflection and axial load-moment interaction curves for CFST slender columns under axial load and uniaxial bending, biaxial loads, preloads or axial load and cyclic lateral loading. The numerical models developed are verified by comparisons of computer solutions with existing experimental results and then utilized to undertake extensive parametric studies on the fundamental behavior of CFST slender columns covering a wide range of parameters. The numerical models are shown to be efficient computer simulation tools for designing safe and economical thin-walled CFST slender beam-columns with any steel and concrete strength grades. The thesis presents benchmark numerical results on the behavior of high strength thin-walled CFST slender beam-columns accounting for progressive local buckling effects. These results provide a better understanding of the fundamental behavior of CFST columns and are valuable to structural designers and composite code writers.

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46

Dasgupta, Titas. "Investigations Of Mechanical And Thermoelectric Properties Of Group (VIB) Transition Metal Disilicides." Thesis, 2007. https://etd.iisc.ac.in/handle/2005/611.

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Transition Metal (TM) silicides are potential materials for diﬀerent high temperature applications due to their high melting points and chemical stability at elevated temperatures. In the present work, the possible use of Gr (VIB) disilicides: MoSi2 and CrSi2 for high temperature structural application and thermopower generation respectively are investigated. Literature reports on MoSi2 indicate this material to have excellent mechanical and thermal behaviors at temperatures greater than 1273 K. The major problems limiting its use are the low temperature brittleness and oxidation at intermediate temperatures and form the scope of this work. Also, CrSi2 is reported to be a narrow band gap semiconductor. Its feasibility as a thermoelectric material for power generation is investigated. The ﬁrst chapter brieﬂy summarizes the literature on MoSi2 and CrSi2 relevant to structural and thermoelectric applications respectively. Based on the available literature, the scope of further work is discussed. The second chapter describes the methods of synthesis employed for these materials and the characterization techniques adopted. Some experimental setups like thermal conductivity and hot pressing unit that were fabricated as part of the work are described in detail. The thermal conductivity apparatus is based on the principle of parallel heat ﬂow technique. It allows accurate measurement of K and S in the temperature range 300-700 K. The induction based hot-pressing unit allows compaction of polycrystalline powders to near theoretical densities thereby allowing quantitative evaluation of the physical properties. In the third chapter, an understanding of ductility/brittleness based of electron charge density distribution is attempted. The electron charge density in Tin and simple metals (BCC and FCC) is analyzed using Bader’s Atoms in Molecule (AIM) theory. Also the relevant surface and dislocation energies in these materials are calculated according to the Rice Model. It is found that the electron densities at the critical points correlate in a simple way with the relevant stacking fault and surface energetics. Based on these results, a ductility parameter (DM odel) based on electron charge distribution, to predict the eﬀects of chemical substitutions on ductility/brittleness in materials is proposed. In the fourth chapter, possible elements to impart ductility in MoSi2 are identiﬁed based on the DM odel values. Calculations indicate, Nb, Ta, Al, Mg and Ga to be suitable candidates for improving ductility in MoSi2. Also oxidation studies based on present experiments and reported literature data reveal, Al to improve the intermediate temperature (773-873 K) oxidation behavior. Thus to simultaneously improve the low temperature ductility and oxidation resistance, Nb and Al were identiﬁed as suitable candidates. In the ﬁfth chapter, the experimental data of Nb and Al co-substituted MoSi2 samples are reported. Oxidation studies carried out by thermogravimetry show improved oxidation resistance in Nb and Al co-substituted samples compared to pure MoSi2 in the temperature range of 773-873 K. Mechanical characterization was carried out for (Mo0.99Nb0.01)(Si0.96Al0.04)2 co-substituted composition. Compression testing at room temperature show plastic deformation at low strain rates (10−3 /sec). Indentation experiments show a reduction in the hardness and stiﬀness compared to pure MoSi2. There is also an increase in the fracture toughness (K1C ) value with the fracture modes being predominantly transgranular. The sixth chapter describes the structural, thermal and transport properties of CrSi2. Structural reﬁnement was carried out by Rietveld method and the positional, thermal parameters and occupancy were ﬁxed. Thermo-gravimetric analysis shows oxidation resistance in powdered samples upto 1000 K. Thermal expansion (α) studies reveal anisotropy in the α values with an unusual decrease in the average αV values between 500 and 600 K. Measurements of electrical resistivity and seebeck coeﬃcient indicate a degenerate semiconducting behavior. Electronic band structure calculations indicate a narrow indirect band gap (EG) material with EG~0.35 eV. Thermal conductivity (K) measurements show a decrease in K value with increasing temperature. Calculation of the thermoelectric ﬁgure of merit (ZT) show a maximum value of 0.18 at 800 K for the temperature range studied. Based on an analysis of the experimental and theoretical results, it is identiﬁed that further improvements in ZT of CrSi2 may be possible by reducing the lattice thermal conductivity and optimization of the carrier concentration. In chapter seven, the eﬀect of particle size on ZT of CrSi2 is studied. Nano powders of CrSi2 were prepared by mechanical milling. Contamination is found to be a major problem during milling and the diﬀerent milling parameters (milling speed, atmosphere, dispersant etc) were optimized to minimize contamination. The milled powders were further hot pressed to achieve high densities in a short duration thereby minimizing the grain growth. It is observed that the lattice thermal conductivity is reduced signiﬁcantly with decreasing grain size. Measurements of ZT show a maximum value of 0.20 in the milled sample compared to 0.14 in arc melted CrSi2 at 600 K. In chapter eight the eﬀect of chemical substitutions on ZT of CrSi2 is studied. Mn substitutions in Cr site were carried out to study the eﬀect of atomic mass on lattice thermal conductivity (KP ). Al substitutions in Si site were carried out to tune the Fermi level. Results of Mn substitution show a large decrease in KP but also a reduction in the thermoelectric power factor (S2σ). The maximum ZT observed in the Mn substituted samples was 0.12 at 600 K. Al substitution results in an increase in the thermoelectric power factor and a subsequent increase in ZT. The maximum ZT observed was 0.27 at 700 K for 10% substitution of Al in Si site. The work reported in the thesis has been carried out by the candidate as a part of the Ph.D. training programme at Materials Research Centre, Indian Institute of Science, Bangalore, India. He hopes that this work would constitute a worthwhile contribution towards (a) basic understanding of ductility/brittleness in materials and understanding the eﬀects of chemical substitutions, (b) Suitability of chemically substituted MoSi2 to overcome the problems of low temperature brittleness and oxidation. (c) Development of CrSi2 as a high temperature thermoelectric material.

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47

Dasgupta, Titas. "Investigations Of Mechanical And Thermoelectric Properties Of Group (VIB) Transition Metal Disilicides." Thesis, 2007. http://hdl.handle.net/2005/611.

Full text

Abstract:

Transition Metal (TM) silicides are potential materials for diﬀerent high temperature applications due to their high melting points and chemical stability at elevated temperatures. In the present work, the possible use of Gr (VIB) disilicides: MoSi2 and CrSi2 for high temperature structural application and thermopower generation respectively are investigated. Literature reports on MoSi2 indicate this material to have excellent mechanical and thermal behaviors at temperatures greater than 1273 K. The major problems limiting its use are the low temperature brittleness and oxidation at intermediate temperatures and form the scope of this work. Also, CrSi2 is reported to be a narrow band gap semiconductor. Its feasibility as a thermoelectric material for power generation is investigated. The ﬁrst chapter brieﬂy summarizes the literature on MoSi2 and CrSi2 relevant to structural and thermoelectric applications respectively. Based on the available literature, the scope of further work is discussed. The second chapter describes the methods of synthesis employed for these materials and the characterization techniques adopted. Some experimental setups like thermal conductivity and hot pressing unit that were fabricated as part of the work are described in detail. The thermal conductivity apparatus is based on the principle of parallel heat ﬂow technique. It allows accurate measurement of K and S in the temperature range 300-700 K. The induction based hot-pressing unit allows compaction of polycrystalline powders to near theoretical densities thereby allowing quantitative evaluation of the physical properties. In the third chapter, an understanding of ductility/brittleness based of electron charge density distribution is attempted. The electron charge density in Tin and simple metals (BCC and FCC) is analyzed using Bader’s Atoms in Molecule (AIM) theory. Also the relevant surface and dislocation energies in these materials are calculated according to the Rice Model. It is found that the electron densities at the critical points correlate in a simple way with the relevant stacking fault and surface energetics. Based on these results, a ductility parameter (DM odel) based on electron charge distribution, to predict the eﬀects of chemical substitutions on ductility/brittleness in materials is proposed. In the fourth chapter, possible elements to impart ductility in MoSi2 are identiﬁed based on the DM odel values. Calculations indicate, Nb, Ta, Al, Mg and Ga to be suitable candidates for improving ductility in MoSi2. Also oxidation studies based on present experiments and reported literature data reveal, Al to improve the intermediate temperature (773-873 K) oxidation behavior. Thus to simultaneously improve the low temperature ductility and oxidation resistance, Nb and Al were identiﬁed as suitable candidates. In the ﬁfth chapter, the experimental data of Nb and Al co-substituted MoSi2 samples are reported. Oxidation studies carried out by thermogravimetry show improved oxidation resistance in Nb and Al co-substituted samples compared to pure MoSi2 in the temperature range of 773-873 K. Mechanical characterization was carried out for (Mo0.99Nb0.01)(Si0.96Al0.04)2 co-substituted composition. Compression testing at room temperature show plastic deformation at low strain rates (10−3 /sec). Indentation experiments show a reduction in the hardness and stiﬀness compared to pure MoSi2. There is also an increase in the fracture toughness (K1C ) value with the fracture modes being predominantly transgranular. The sixth chapter describes the structural, thermal and transport properties of CrSi2. Structural reﬁnement was carried out by Rietveld method and the positional, thermal parameters and occupancy were ﬁxed. Thermo-gravimetric analysis shows oxidation resistance in powdered samples upto 1000 K. Thermal expansion (α) studies reveal anisotropy in the α values with an unusual decrease in the average αV values between 500 and 600 K. Measurements of electrical resistivity and seebeck coeﬃcient indicate a degenerate semiconducting behavior. Electronic band structure calculations indicate a narrow indirect band gap (EG) material with EG~0.35 eV. Thermal conductivity (K) measurements show a decrease in K value with increasing temperature. Calculation of the thermoelectric ﬁgure of merit (ZT) show a maximum value of 0.18 at 800 K for the temperature range studied. Based on an analysis of the experimental and theoretical results, it is identiﬁed that further improvements in ZT of CrSi2 may be possible by reducing the lattice thermal conductivity and optimization of the carrier concentration. In chapter seven, the eﬀect of particle size on ZT of CrSi2 is studied. Nano powders of CrSi2 were prepared by mechanical milling. Contamination is found to be a major problem during milling and the diﬀerent milling parameters (milling speed, atmosphere, dispersant etc) were optimized to minimize contamination. The milled powders were further hot pressed to achieve high densities in a short duration thereby minimizing the grain growth. It is observed that the lattice thermal conductivity is reduced signiﬁcantly with decreasing grain size. Measurements of ZT show a maximum value of 0.20 in the milled sample compared to 0.14 in arc melted CrSi2 at 600 K. In chapter eight the eﬀect of chemical substitutions on ZT of CrSi2 is studied. Mn substitutions in Cr site were carried out to study the eﬀect of atomic mass on lattice thermal conductivity (KP ). Al substitutions in Si site were carried out to tune the Fermi level. Results of Mn substitution show a large decrease in KP but also a reduction in the thermoelectric power factor (S2σ). The maximum ZT observed in the Mn substituted samples was 0.12 at 600 K. Al substitution results in an increase in the thermoelectric power factor and a subsequent increase in ZT. The maximum ZT observed was 0.27 at 700 K for 10% substitution of Al in Si site. The work reported in the thesis has been carried out by the candidate as a part of the Ph.D. training programme at Materials Research Centre, Indian Institute of Science, Bangalore, India. He hopes that this work would constitute a worthwhile contribution towards (a) basic understanding of ductility/brittleness in materials and understanding the eﬀects of chemical substitutions, (b) Suitability of chemically substituted MoSi2 to overcome the problems of low temperature brittleness and oxidation. (c) Development of CrSi2 as a high temperature thermoelectric material.

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48

Al-Jabr, Khalid A. "Multiscale Modeling of Hydrogen Embrittlement for Multiphase Material." Diss., 2014. http://hdl.handle.net/10754/316598.

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Hydrogen Embrittlement (HE) is a very common failure mechanism induced crack propagation in materials that are utilized in oil and gas industry structural components and equipment. Considering the prediction of HE behavior, which is suggested in this study, is one technique of monitoring HE of equipment in service. Therefore, multi-scale constitutive models that account for the failure in polycrystalline Body Centered Cubic (BCC) materials due to hydrogen embrittlement are developed. The polycrystalline material is modeled as two-phase materials consisting of a grain interior (GI) phase and a grain boundary (GB) phase. In the first part of this work, the hydrogen concentration in the GI (Cgi) and the GB (Cgb) as well as the hydrogen distribution in each phase, were calculated and modeled by using kinetic regime-A and C, respectively. In the second part of this work, this dissertation captures the adverse effects of hydrogen concentration, in each phase, in micro/meso and macro-scale models on the mechanical behavior of steel; e.g. tensile strength and critical porosity. The models predict the damage mechanisms and the reduction in the ultimate strength profile of a notched, round bar under tension for different hydrogen concentrations as observed in the experimental data available in the literature for steels. Moreover, the study outcomes are supported by the experimental data of the Fractography and HE indices investigation. In addition to the aforementioned continuum model, this work employs the Molecular Dynamics (MD) simulations to provide information regarding bond formulation and breaking. The MD analyses are conducted for both single grain and polycrystalline BCC iron with different amounts of hydrogen and different size of nano-voids. The simulations show that the hydrogen atoms could form the transmission in materials configuration from BCC to FCC (Face Centered Cubic) and HCP (Hexagonal Close Packed). They also suggest the preferred sites of hydrogen for each case. The connections between the results for different scales (nano, micro/meso and macro-scale) were suggested in this dissertation and show good agreements between them. We finally conclude that hydrogen-induced steel fracture and the change of fracture mode are caused by the suppression of dislocation emission at crack tip and changing in the material structure due to accumulation of hydrogen, which is driven by the stress fields. This causes the brittle fracture to occur as inter-granular in the GB and trans-granular in the GI.

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49

Fan, Chen-wei, and 范晨緯. "Ductility of Steel Beam-to-Column Connections with Concrete as Fire Protection Material." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/08600580817795661932.

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碩士
國立臺灣科技大學
營建工程系
97
RBS (Reduced Beam Section) is commonly used for beam-to-column connections of steel structures. However, when concrete cover is used as fire protection layer, the details of the beam-to-column connection should be assessed regarding the ductility and the serviceability of the connection. In this research, 5 sets of beam-column subassemblies were fabricated and tested under cyclic loading to investigate the behavior of the beam-to-column connections with various structural details. NR specimen used untreated beam-to-column connection, R1 specimen used 95% moment capacity and 1/2 beam depth RBS, R2-I specimen used 90% moment capacity and 2/3 beam depth RBS with isolation for bond stress in RBS portion, R2-C specimen used 90% moment capacity and 2/3 beam depth RBS with CAP(Composition Action Plate), and, R2-C used 90% moment capacity and 2/3 beam depth RBS, CAP, and with longitudinal reinforcing bars connected to the box column by coupler. Test results shows that：(1) beam-to-column connection without RBS possessed only 1.73% of plastic hinge rotation capacity, which is not sufficient for earthquake-resistant structures；(2) Specimens using RBS possessed a plastic hinge rotation capacity of about 3%, which is considered comparable to pure steel beam-to-column connections with RBS；(3) The compression strut induced by CAP provided extra path to transfer shear force；(4) Connecting longitudinal reinforcing bars to box column by coupler can obviously improve the serviceability of the structure; (5) it is suggested that RBS should be used for steel beam-to-column connections with concrete cover as fire protection layer; and (6) It is suggested that longitudinal reinforcing bars should not anchor to column concrete with 90 degree hook, instead, it is suggested to cut the reinforcing bars at the position of column concrete surface.

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50

Coelho, Ana Margarida Girão. "Characterization of the ductility of bolted end plate beam-to-column steel connections." Doctoral thesis, 2004. http://hdl.handle.net/10316/1980.

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Tese de doutoramento em Engenharia Civil (Mecânica das Estruturas e dos Materiais) apresentada à Fac. de Ciências e Tecnologia da Univ. de Coimbra
O projecto de estruturas metálicas para edifícios porticados com ligações viga-pilar de resistência total é relativamente comum. No entanto, tem-se vindo a reconhecer os benefícios que decorrem da modelação semi-rígida e de resistência parcial das ligações. Esta abordagem tem-se generalizado no dimensionamento das ligações metálicas. Para o efeito, é necessário avaliar o comportamento momento-rotação real das ligações. Além disso, a rotura das ligações tem de ser dúctil, isto é, as ligações têm de exibir capacidade de rotação suficiente, uma vez que as primeiras rótulas plásticas se formam no nó de ligação e não nos elementos (viga ou pilar). O trabalho de investigação apresentado nesta tese foca este aspecto e dá ênfase à caracterização da ductilidade das ligações, que é particularmente relevante na modelação semi-rígida/resistência parcial. Descrevem-se e discutem-se os resultados experimentais e numéricos de sessenta e um testes em ligações em duplo T (T-stubs) individuais e oito ligações viga-pilar aparafusadas com placa de extremidade. A análise destes resultados inclui a caracterização das propriedades de resistência, rigidez e ductilidade das ligações e a sua confrontação com modelos correntes de avaliação de resistência e rigidez. Em termos de ductilidade, é proposta uma metodologia simplificada baseada no método das componentes para a caracterização desta propriedade das ligações. Uma vez que a rotação da ligação provém essencialmente da deformação da placa de extremidade, no caso de placas finas, a idealização do seu comportamento por meio de T-stubs equivalentes é particularmente relevante. Um modelo mecânico de molas e bielas rígidas que inclui a idealização da zona traccionada por intermédio de T-stubs é utilizado para a caracterização da resposta momento-rotação da ligação, com particular ênfase na avaliação da sua ductilidade. Estabelecem-se comparações entre a ductilidade da ligação e os correspondentes T-stubs equivalentes na zona da placa de extremidade. Finalmente, são propostas algumas recomendações para a ductilidade mínima da ligação, expressa em termos de um índice de ductilidade.

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Dissertations / Theses on the topic 'Materials - Ductility'

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