Academic literature on the topic 'Strain mechanisms; dislocations'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the lists of relevant articles, books, theses, conference reports, and other scholarly sources on the topic 'Strain mechanisms; dislocations.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Journal articles on the topic "Strain mechanisms; dislocations"
1
Jenei, Péter, Guy Dirras, Jenő Gubicza, and Hervé Couque. "Deformation Mechanisms in Ultrafine-Grained Zn at Different Strain Rates and Temperatures." Key Engineering Materials 592-593 (November 2013): 313–16. http://dx.doi.org/10.4028/www.scientific.net/kem.592-593.313.
Full textAbstract:
The deformation mechanisms in ultrafine-grained hexagonal close packed Zn were investigated at different strain rates and temperatures. The influence of grain size on the deformation mechanisms was revealed by comparing the results obtained on ultrafine-grained and coarse-grained Zn. It was found that for coarse-grained Zn at room temperature and strain rates lower than 10-2s-1twinning contributed to plasticity besides dislocation activity. For strain rates higher than 103s-1the plasticity in coarse-grained Zn was controlled by dislocation drag. In ultrafine-grained Zn the relatively large dislocation density (~1014m-2) and the small grain size (~250 nm) limit the dislocation velocity yielding the lack of dislocation drag effects up to 104s-1. For ultrafine-grained Zn, twinning was not observed in the entire strain rate range due to its very small grain size. During room temperature compression at strain rates higher than 0.35 s-1and in high temperature creep deformation of ultrafine-grained Zn besides prismatic and pyramidal <c+a> dislocations observed in the initial state, <a>-type basal and pyramidal dislocations as well as other <c+a>-type pyramidal dislocations were formed.
2
Nazé, Loic, and Jean Loup Strudel. "Strain Rate Effects and Hardening Mechanisms in Ni Base Superalloys." Materials Science Forum 638-642 (January 2010): 53–60. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.53.
Full textAbstract:
The mechanical properties of nickel superalloys are related to the spatial distribution of hardening phases, their size and composition, and on the configurations of dislocations introduced by plastic and viscoplastic straining. Heterogeneous plastic flow in relation with dynamic strain aging is examined and synthesized. Dislocations are usually faced with the alternative of shearing or bypassing the ’ phase occupying up to 60 vol.%. Depending on ’ size, several Orowan bypassing mechanisms are observed, alternatively shearing by dislocation pairs or complex configurations involving S-ISF and S-ESF. Variables such as temperature, strain rate and Schmid factor play a decisive role in determining the dislocation configurations which either percolate through the matrix or shear the ’ structure. Various dislocation strategies and microstructures are analyzed and illustrated; they are reviewed critically and summarized in a strain rate versus 1/T mechanism map.
3
Mughrabi, Haël. "On the dislocation mechanisms of dynamic strain ageing in fatigued plain carbon steels." International Journal of Materials Research 94, no. 5 (2003): 471–77. http://dx.doi.org/10.1515/ijmr-2003-0085.
Full textAbstract:
Abstract The fatigue life of plain ferritic carbon steels fatigued in stress-controlled (plastic-strain-controlled) tests exhibits a maximum (minimum) at a temperature of approx. 300 °C as a result of dynamic strain ageing (DSA). In the regime of DSA, an enhanced cyclic hardening related to an increased dislocation density is observed, and the dislocation arrangement changes from a dislocation cell structure (at intermediate stress amplitudes) at room temperature to a dense edge di-/multipolar bundle/wall/vein structure in the temperature range of DSA and back to a dislocation cell/ subgrain structure at higher temperatures. Related effects occur also in α-iron containing some carbon when fatigued at room temperature at a very low strain rate. This behaviour is considered to be typical of body-centred cubic materials. In the present study, the dislocation mechanisms responsible for this behaviour are discussed in detail, and a dislocation glide model is developed which can explain both the enhanced dislocation density and the change of the dislocation arrangement in the regime of DSA. The model is based on the different mobilities of mobile edge and less mobile screw dislocations in body-centred cubic metals and on the strong tendency towards multiple slip leading to a dislocation cell structure at lower temperatures. In the regime of DSA, it is proposed that the edge dislocations are hindered more strongly in their glide motion by the solute carbon atoms than the screw dislocations so that screws and edges are then more or less equally mobile. Taking into account that screw dislocations of opposite sign annihilate mutually by cross slip, this explains the observed dislocation arrangement of dense edge di-/multipolar bundles/ walls/veins of high dislocation density which, in turn, leads to an enhanced cyclic hardening rate. The dislocation sub-grain structure observed at higher temperatures reflects the increasing tendency for the transformation from dislocation cell to subgrain structures, as the temperature is increased.
4
He, Yang-Yu, Zhao-Hui Zhang, Yi-Fan Liu, et al. "Ultra-High Strength and Specific Strength in Ti61Al16Cr10Nb8V5 Multi-Principal Element Alloy: Quasi-Static and Dynamic Deformation and Fracture Mechanisms." Materials 18, no. 14 (2025): 3245. https://doi.org/10.3390/ma18143245.
Full textAbstract:
This study investigates the deformation and fracture mechanisms of a Ti61Al16Cr10Nb8V5 multi-principal element alloy (Ti61V5 alloy) under quasi-static and dynamic compression. The alloy comprises an equiaxed BCC matrix (~35 μm) with uniformly dispersed nano-sized B2 precipitates and a ~3.5% HCP phase along grain boundaries, exhibiting a density of 4.82 g/cm3, an ultimate tensile strength of 1260 MPa, 12.8% elongation, and a specific strength of 262 MPa·cm3/g. The Ti61V5 alloy exhibits a pronounced strain-rate-strengthening effect, with a strain rate sensitivity coefficient (m) of ~0.0088 at 0.001–10/s. Deformation activates abundant {011} and {112} slip bands in the BCC matrix, whose interactions generate jogs, dislocation dipoles, and loops, evolving into high-density forest dislocations and promoting screw-dominated mixed dislocations. The B2 phase strengthens the alloy via dislocation shearing, forming dislocation arrays, while the HCP phase enhances strength through a dislocation bypass mechanism. At higher strain rates (960–5020/s), m increases to ~0.0985. Besides {011} and {112}, the BCC matrix activates high-index slip planes {123}. Intensified slip band interactions generate dense jogs and forest dislocations, while planar dislocations combined with edge dislocation climb enable obstacle bypassing, increasing the fraction of edge-dominated mixed dislocations. The Ti61V5 alloy shows low sensitivity to adiabatic shear localization. Under forced shear, plastic-flow shear bands form first, followed by recrystallized shear bands formed through a rotational dynamic recrystallization mechanism. Microcracks initiate throughout the shear bands; during inward propagation, they may terminate upon encountering matrix microvoids or deflect and continue when linking with internal microcracks.
5
Shimokawa, Tomotsugu, Toshiyasu Kinari, and Sukenori Shintaku. "Atomic Simulations on the Grain Subdivision of a Crystalline Metal." Materials Science Forum 561-565 (October 2007): 1983–86. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.1983.
Full textAbstract:
The relationship between grain subdivision mechanisms of a crystalline metal and the strain gradient under severe plastic deformation is studied by using molecular dynamics simulations in quasi two dimensions. Two problems are simulated for single crystal models: (a) uniaxial tensile and compressive deformation and (b) localized shear deformation. In the case of uniaxial deformation, a large number of dislocation pairs with opposite Burgers vectors are generated under deformation, but most dislocations are vanished due to pair annihilation under relaxation. Therefore, no dislocation boundary can be formed. On the other hand, in case of localized shear deformation with large strain gradient, dislocation boundaries are formed between undeformed and deformed regions. These dislocations can be regarded as geometrically necessary dislocations. Consequently, the importance of the strain gradient to make grain boundaries under plastic deformation can be confirmed by atomic simulations.
6
Belyakov, Andrey, Marina Odnobokova, Iaroslava Shakhova, and Rustam Kaibyshev. "Regularities of Microstructure Evolution and Strengthening Mechanisms of Austenitic Stainless Steels Subjected to Large Strain Cold Working." Materials Science Forum 879 (November 2016): 224–29. http://dx.doi.org/10.4028/www.scientific.net/msf.879.224.
Full textAbstract:
The deformation microstructures and their effects on mechanical properties of austenitic stainless steels processed by cold rolling at ambient temperature to various total strains were studied. The cold working was accompanied by the development of strain-induced martensitic transformation because of meta-stable austenite at room temperature. The strain-induced martensitic transformation and deformation twinning promoted the grain refinement during cold rolling, leading to nanocrystalline structures consisting of a mixture of austenite and martensite grains with their transverse grain sizes of 50-150 nm containing high dislocation densities. The rolled samples experienced substantial strengthening resulted from high density of strain induced grain/phase boundaries and dislocations. The yield strength of austenitic stainless steels could be increased to 2000 MPa after rolling to total strains of about 4. The martensite and austenite provided almost the same contribution to overall yield strength. The dislocation strengthening was much higher than the grain boundary strengthening at small to moderate strains of about 2, whereas the latter gradually increased approaching the level of dislocation strengthening with increasing the strain.
7
Solov’eva, Yu V., A. N. Solov’ev, M. V. Gettinger, O. D. Pantyukhova, and V. A. Starenchenko. "Contributions of various mechanisms to the flow stress in Cu – 12 at. % Al single crystals." Deformation and fracture of materials, no. 1 (2022): 19–26. http://dx.doi.org/10.31044/1814-4632-2022-1-19-26.
Full textAbstract:
The evolution of the structure in the process of plastic deformation by compression of Cu – 12 at.% Al single crystals is investigated. Data on the stress-strain curve, deformation stages and the relationship of stages with the types of forming substructures are presented. Quantitative measurements of various parameters characterizing the substructures were carried out. The results are presented in the form of a diagram of the dependence of the fraction of substructures on the density of dislocations. Dependences of the distances between non-reactive intersections of dislocations, inter-dislocation reactions, obstacles of different types, and dislocation lines on the degree of strain are shown. Particular attention is paid to the quantitative assessment of the contributions to the flow stress from local obstacles and long-range elastic stress fields, as well as the contributions to strain associated with the development of slip and twinning.
8
Chang, Shou-Yi, Yi-Chung Huang, Shao-Yi Lin, Chia-Ling Lu, Chih Chen, and Ming Dao. "In Situ Study of Twin Boundary Stability in Nanotwinned Copper Pillars under Different Strain Rates." Nanomaterials 13, no. 1 (2023): 190. http://dx.doi.org/10.3390/nano13010190.
Full textAbstract:
The nanoscopic deformation of ⟨111⟩ nanotwinned copper nanopillars under strain rates between 10−5/s and 5 × 10−4/s was studied by using in situ transmission electron microscopy. The correlation among dislocation activity, twin boundary instability due to incoherent twin boundary migration and corresponding mechanical responses was investigated. Dislocations piled up in the nanotwinned copper, giving rise to significant hardening at relatively high strain rates of 3–5 × 10−4/s. Lower strain rates resulted in detwinning and reduced hardening, while corresponding deformation mechanisms are proposed based on experimental results. At low/ultralow strain rates below 6 × 10−5/s, dislocation activity almost ceased operating, but the migration of twin boundaries via the 1/4 ⟨101¯ ⟩ kink-like motion of atoms is suggested as the detwinning mechanism. At medium strain rates of 1–2 × 10−4/s, detwinning was decelerated likely due to the interfered kink-like motion of atoms by activated partial dislocations, while dislocation climb may alternatively dominate detwinning. These results indicate that, even for the same nanoscale twin boundary spacing, different nanomechanical deformation mechanisms can operate at different strain rates.
9
Lee, W.-S., C.-F. Lin, and B.-T. Chen. "Tensile properties and microstructural aspects of 304L stainless steel weldments as a function of strain rate and temperature." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 219, no. 5 (2005): 439–51. http://dx.doi.org/10.1243/095440605x17045.
Full textAbstract:
This paper presents an investigation into the effects of loading rate and temperature on the tensile properties and microstructural evolution of 304L stainless steel weldments. The stress-strain behaviour during tension was determined by loading specimens in a material testing system at strain rates ranging from 10−3 to 10−1 s−1 and temperatures between −100 and 500°. Extensive quantitative microstructural examinations were performed to identify the correlation between the tensile response and the substructure of dislocations and α’ martensite. It was found that the tensile flow stress increased with increasing strain rate, but decreased with increasing temperature. For a test conducted below room temperature, a negative strain rate sensitivity was apparent at strains exceeding 0.3. Fracture feature examination revealed that an enhanced fracture resistance was evident in the base metal at low temperatures, whereas it is evident in the weld metal at high temperatures owing to their different hardening rates and microstructural states. Microstructural analysis revealed that both the dislocation density and the α’ martensite volume fraction increased with increasing strain rate, but decreased as the temperature was increased. In the range of -100-25°, both dislocations and α' martensite enhanced the strength of the tested weldment. However, between 300 and 500°, the strengthening effect was dominated only by dislocation mechanisms. For a given strain rate and temperature, a higher dislocation density existed in the weld metal, whereas a larger volume fraction of α' martensite was present in the base metal. Both increased dislocations and volume fractions of α' martensite yielded a greater work-hardening stress.
10
Kvam, E. P., D. M. Maher, and C. J. Humphreys. "Variation of dislocation morphology with strain in GexSi1−x epilayers on (100)Si." Journal of Materials Research 5, no. 9 (1990): 1900–1907. http://dx.doi.org/10.1557/jmr.1990.1900.
Full textAbstract:
A change in microstructure, including dislocation Burgers vector, length, and behavior, has been observed to occur when the epilayer mismatch is varied in GexSi1−x layers grown on (100) Si. At low mismatches (<1.5%), there is an orthogonal array of very long 60° misfit dislocations. At higher mismatches (>2.3%) there is an orthogonal array of short edge dislocations. At intermediate mismatches (1.5 to 2.3%) there is a mixture of 60° and edge dislocations. The nature of the microstructure has a pronounced effect on the density of threading dislocations in the epilayer, which increase by a factor of ∼60× through a relatively small range of mismatch (1.7 to 2.1%, corresponding to x ranging from 0.4 to 0.5). These morphologies are discussed in the light of recent work on the sources of misfit dislocations. While mechanisms for the introduction and propagation of dislocations at low mismatch have recently been observed and explained, the high misfit case is clearly very different; i.e., surface nucleation seems to be likely in the latter case as opposed to operation of an internal source in the former. A mechanism for edge dislocation formation is proposed.
Dissertations / Theses on the topic "Strain mechanisms; dislocations"
1
Fowler, Rebecca M. "Identification of deformation mechanisms during bi-axial straining of superplastic AA5083 material." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://handle.dtic.mil/100.2/ADA432796.
Full text
2
Torabiandehkordi, Noushin. "High and very high cycle fatigue behavior of DP600 dual-phase steel : correlation between temperature, strain rate, and deformation mechanisms." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0020/document.
Full textAbstract:
Ce travail vise à améliorer notre compréhension du comportement en fatigue à grand et très grand nombre de cycles d’un acier ferrito-martensitique dual phase, notamment les effets de la température et de la vitesse de déformation résultant de chargements cycliques à haute fréquence. L'effet de la fréquence sur la réponse en fatigue de l'acier DP600 a été étudié en effectuant des essais de fatigue sur une machine ultrasonique travaillant à 20 kHz et sur une machine conventionnelle travaillant à des fréquences inférieures à 100 Hz. Des études de fractographie et des observations microscopiques à la surface des échantillons ont été effectuées pour étudier les mécanismes de déformation et de rupture. De plus, la thermographie infrarouge in situ a été utilisée pour étudier la réponse thermique et les mécanismes dissipatifs du matériau lors des essais de fatigue. Les courbes S-N ont été déterminées à partir de chargements de fatigue ultrasoniques à 20 kHz et d’essais conventionnels à 30 Hz. La durée de vie pour une amplitude de contrainte donnée est plus élevée dans le cas de la fatigue ultrasonique bien que la limite de fatigue soit identique dans les deux cas. L’augmentation inévitable de la température en fatigue ultrasonique à fortes amplitudes de contraintes, ainsi que le comportement dépendant de la vitesse de déformation de la ferrite, en tant que structure CC, ont été trouvés comme les paramètres clés expliquant le comportement observé en fatigue, et la réponse thermique sous les fréquences faibles et ultrasoniques. Les écarts observés entre l’essai de fatigue conventionnel et celui ultrasonique ont été évalués à travers les mécanismes de mobilité des dislocations vis dans la phase ferritique de structure cubique centrée (CC). La durée de vie plus élevée et l’amorçage de la fissure principale sur une inclusion observés en fatigue ultrasonique ont été attribués au vieillissement dynamique résultant du fort auto-échauffement du matériau aux fortes amplitudes de contraintes. L'existence d'une transition du régime thermiquement activé au régime athermique avec l’augmentation de l'amplitude de contrainte a été mise en évidence. Au-dessous de la limite de fatigue, la déformation a lieu dans un régime thermiquement activé alors qu'elle est dans un régime athermique au-dessus de la limite de fatigue. En fatigue conventionnelle, la déformation est athermique pour toutes les amplitudes de contrainte. Une carte de transition a été produite en utilisant les résultats expérimentaux pour l'acier DP600 ainsi que les données disponibles dans la littérature pour d'autres aciers à base de ferrite, montrant ainsi la corrélation entre le mouvement des dislocations vis thermiquement activé et l'absence de rupture en fatigue à très grand nombre de cycle<br>This work is an attempt towards a better understanding of the high cycle and very high cycle fatigue behaviors of a ferritic-martensitic dual-phase steel, with a regard to temperature and strain rate effects, resulting from accelerated fatigue loading frequencies. The influence of frequency on fatigue response of DP600 steel was investigated by conducting ultrasonic and conventional low frequency fatigue tests. Fractography studies and microscopic observations on the surface of specimens were carried out to study the deformation and fracture mechanisms under low and ultrasonic frequencies. Moreover, in situ infrared thermography was carried out to investigate the thermal response and dissipative mechanisms of the material under fatigue tests. The S-N curves were determined from ultrasonic 20-kHz fatigue loadings and conventional tests at 30 Hz. Fatigue life for a given stress amplitude was found to be higher in the case of ultrasonic fatigue whereas the fatigue limit was the same for both cases. Moreover, crack initiation was always inclusion-induced under ultrasonic loading while under conventional tests it occurred at slip bands or defects on the surface. The inevitable temperature increase under ultrasonic fatigue at high stress amplitudes along with the rate dependent deformation behavior of ferrite, as a body centered cubic (BCC) structure, were found as the key parameters explaining the observed fatigue behavior and thermal response under low and ultrasonic frequencies. The discrepancies observed between conventional and ultrasonic fatigue tests were assessed through the mechanisms of screw dislocation mobility in the ferrite phase as a BCC structure. The higher fatigue life and inclusion-induced crack initiations in the case of ultrasonic loading were attributed to the dynamic strain aging, which resulted from the high temperature increases at high stress amplitudes. The existence of a transition in deformation regime from thermally-activated to athermal regime under ultrasonic fatigue loading by increasing the stress amplitude was confirmed. Below the fatigue limit, deformation occurred in thermally-activated regime while it was in athermal regime above the fatigue limit. Under conventional loading deformation occurred in athermal regime for all stress amplitudes. From the analysis of the experimental data gathered in this work, guidelines were given regarding the comparison and interpretation of S-N curves obtained from conventional and ultrasonic fatigue testing. A transition map was produced using the experimental results for DP600 steel as well as data available in the literature for other ferrite based steels, showing the correlation between thermally-activated screw dislocation movement and the absence of failure in very high cycle fatigue
3
Schayes, Claire. "Low cycle fatigue of the Fe-3Si steel : damage mechanisms and strain localisation by EBSD." Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10002/document.
Full textAbstract:
L’objectif de ce travail de thèse était d’étudier le comportement en fatigue oligocyclique de l’acier Fe-3Si utilisé pour les rotors des nouveaux alterno-démarreurs développés par Valeo. L’étude pris en compte la relation entre la réponse mécanique et la microstructure, les mécanismes de fatigue, l’évaluation de la déformation à une échelle mésoscopique et une optimisation du dimensionnement du rotor. Les essais de fatigue, menés sur des éprouvettes d’épaisseur 350μm, ont montré un durcissement cyclique du matériau et le mode de propagation de la fissure, fragile, souligne sa faible ténacité. La formation de structure de dislocations observées par Microscopie Electronique en Transmission (TEM) et par cECCI (Controlled Electron Channelling Contrast Imaging) est dépendante de la déformation et la variation de déformation totale Δεt=0.7% apparaît comme une valeur de transition. En-dessous de Δεt =0.7%, des arrangements homogènes de dislocations et un amorçage de la fissure transgranulaire sont observés. Au-dessus de Δεt =0.7%, des structures veines-canaux et murs-canaux sont observés et l'amorçage de fissure est intergranulaire. Une étude EBSD (Electron Back-Scattered Diffraction) basée sur les paramètres KAM, GROD et GOS menée sur les éprouvettes fatiguées montre un gradient de déformation dans les grains et une localisation de la déformation aux joints de grain au-dessus de Δεt =0.7%. Enfin, en prenant en compte les propriétés en fatigue de l’acier Fe-3Si dans la base de données matériaux de la modélisation par éléments finis, des légères modifications de la géométrie du rotor ont été effectuées ce qui améliore les performances électromagnétiques de la machine<br>The objective of the PhD work was to investigate the low cycle fatigue (LCF) behaviour of Fe-3Si steel employed for rotors of new starter-alternators developed by Valeo. The study took into account the relation between mechanical response and microstructure, the fatigue mechanisms, the assessment of strain at a mesoscopic scale and an optimisation of the rotor design. Low cycle fatigue tests performed on 350μm thick specimen pointed out a cyclic hardening of the material. The brittle crack propagation mode underlined the low toughness of the material. The formation of dislocations structures observed by Transmission Electron Microscopy (TEM) and controlled Electron Channelling Contrast Imaging (cECCI) was strain dependant. The total strain variation Δεt =0.7% appeared as a transition value. Below Δεt =0.7%, homogeneous arrangement of dislocations and transgranular crack initiation are observed. Above Δεt =0.7%, a mixture of veins-channels and wall-channels were observed inside the grains and cracking became intergranular. An Electron Back-Scattered Diffraction (EBSD) study was then performed on the specimen fatigued above Δεt=0.7% and approached with KAM, GROD and GOS parameters. It pointed out the strain gradient within grain and highlighted the strain localisation at grain boundaries. Finally, by taking into account LCF properties of the Fe-3Si steel in the material database of the finite element modelling, slight modifications of the rotor geometry have been performed which improves the electromagnetic performances of the machine
4
Shehadeh, Mu'Tasem A. "Modeling of high strain rate and strain localization in FCC single crystals multiscale dislocation dynamics analyses /." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Spring2005/M%5FShehadeh%5F050405.pdf.
Full text
5
Li, Quantong. "Strain relaxation in InGaN/GaN herostructures." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC204/document.
Full textAbstract:
Dans ce travail, nous avons étudié la relaxation de couches d’hétérostructures InGaN/GaN obtenue par épitaxie en phase vapeur aux organométalliques (EPVOM) et épitaxie aux jets moléculaires (EJM) principalement par microscopie électronique en transmission (MET). Pour ce faire, nous avons fait varier la composition de l'indium de 4.1% au nitrure d'indium pur, ce qui correspond lors de la croissance sur GaN à un décalage paramétrique allant de 1% à 11.3%. Le travail a porté sur des couches dont l’épaisseur allait de 7 nm à 500 nm. A partir d’une composition en indium voisine de 10%, nous mettons en évidence la formation d’un réseau de dislocations vis dont la ligne se promène dans l’interface, avec de très longues sections droites le long des directions <11-20>. Ces dislocations coexistent avec un réseau de dislocations coins qui commence à se former vers 13%, il disparait complétement autour d’une composition en indium de 18%. Le réseau de dislocation vis se densifie de plus en plus au-delà. Outre ces dislocations de décalage paramétrique, d'autres mécanismes qui contribuent à la relaxation de la contrainte dans ces hétérostructures InGaN/GaN ont été mis en évidence. Ainsi, au-dessus d'une composition d'indium supérieure à 25%, de nombreux phénomènes se produisent simultanément. (1) Formation des dislocations de décalage paramétrique à l'hétérointerface; (2) une composition de la couche qui s’enrichit en indium vers la surface; (3) des fortes perturbations de la séquence hexagonale conduisant à un empilement aléatoire; (4) croissance à trois dimensions (3D) pouvant même conduire à des couches poreuses lorsque la composition en indium est comprise entre 40% et 85%. Cependant, on met en évidence qu’il est possible de faire croître de l’InN pur de bonne qualité cristalline s'améliore grâce à la formation systématique d'une couche 3D<br>In this work, we have investigated the strain relaxation of InGaN layers grown on GaN templates by MOVPE and PAMBE using TEM. To this end we varied the indium composition from 4.1% to pure indium nitride and the corresponding mismatch was changing from less than 1% to 11.3%, the thickness of the InGaN layers was from 7 nm to 500 nm. When the indium composition is around 10%, one would expect mostly elastically strained layers with no misfit dislocations. However, we found that screw dislocations form systematically at the InGaN/GaN interface. Moreover, below 18% indium composition, screw and edge dislocations coexist, whereas starting at 18%, only edge dislocations were observed in these interfaces. Apart from the edge dislocations (misfit dislocations), other mechanisms have been pointed out for the strain relaxation. It is found that above an indium composition beyond 25%, many phenomena take place simultaneously. (1) Formation of the misfit dislocations at the heterointerface; (2) composition pulling with the surface layer being richer in indium in comparison to the interfacial layer; (3) disruption of the growth sequence through the formation of a random stacking sequence; (4) three dimentional (3D) growth which can even lead to porous layers when the indium composition is between 40% and 85%. However, pure InN is grown, the crystalline quality improves through a systematic formation of a 3D layer
6
Hu, Jindong, and 胡勁東. "Elastic fracture of annulated structures analyzed by distributed dislocation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31241785.
Full text
7
Degli, Alessandrini Giulia. "Deformation mechanisms and strain localization in the mafic continental lower crust." Thesis, University of Plymouth, 2018. http://hdl.handle.net/10026.1/12799.
Full textAbstract:
The rheology and strength of the lower crust play a key role in lithosphere dynamics, influencing the orogenic cycle and how plate tectonics work. Despite their geological importance, the processes that cause weakening of the lower crust and strain localization are still poorly understood. Through microstructural analysis of naturally deformed samples, this PhD aims to investigate how weakening and strain localization occurs in the mafic continental lower crust. Mafic granulites are analysed from two unrelated continental lower crustal shear zones which share comparable mineralogical assemblages and high-grade deformation conditions (T > 700 °C and P > 6 Kbar): the Seiland Igneous Province in northern Norway (case-study 1) and the Finero mafic complex in the Italian Southern Alps (case-study 2). Case-study 1 investigates a metagabbroic dyke embedded in a lower crustal metasedimentary shear zone undergoing partial melting. Shearing of the dyke was accompanied by infiltration of felsic melt from the adjacent partially molten metapelites. Findings of case-study 1 show that weakening of dry and strong mafic rocks can result from melt infiltration from nearby partially molten metasediments. The infiltrated melt triggers melt-rock reactions and nucleation of a fine-grained (< 10 µm average grain size) polyphase matrix. This fine-grained mixture deforms by diffusion creep, causing significant rheological weakening. Case-study 2 investigates a lower crustal shear zone in a compositionally-layered mafic complex made of amphibole-rich and amphibole-poor metagabbros. Findings of case-study 2 show that during prograde metamorphism (T > 800 °C), the presence of amphibole undergoing dehydration melting reactions is key to weakening and strain localization. Dehydration of amphibole generates fine-grained symplectic intergrowths of pyroxene + plagioclase. These reaction products form an interconnected network of fine-grained (< 20 µm average grain size) polyphase material that deforms by diffusion creep, causing strain partitioning and localization in amphibole-rich layers. Those layers without amphibole fail to produce an interconnected network of fine grained material. In this layers, plagioclase deforms by dislocation creep, and pyroxene by microfracturing and neocrystallization. Overall, this PhD research highlights that weakening and strain localization in the mafic lower crust is governed by high-T mineral and chemical reactions that drastically reduce grain size and trigger diffusion creep.
8
Fredriksson, Per. "Modelling and simulation of plastic deformation on small scales : interface conditions and size effects of thin films." Doctoral thesis, Stockholm : Hållfasthetslära, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4652.
Full text
9
ZHOU, XIAO-WEI. "Contribution au comportement dynamique des materiaux metalliques : etude experimentale de l'alliage al-li en torsion et en compression, simulation numerique du processus de penetration a grande vitesse." Nantes, 1988. http://www.theses.fr/1988NANT2014.
Full textAbstract:
Etude experimentale sur les alliages al-li soumis a des essais de traction et de compression pour des vitesses de deformation comprises entre 10**(-4) et 310**(3) s**(-1) et de 10**(-3) a 210**(3) s**(-1) respectivement. Auparavant ces alliages ont ete traites thermiquement. Analyse de la sensibilite a la vitesse de deformation. Influence du mecanisme d'activation thermique sur le processus de deformation. Determination du mode de rupture. Analyse des facies de rupture pour les echantillons deformes en traction et de la formation des cellules de dislocation dans ceux deformes en compression. Simulation numerique du processus de penetration a grande vitesse d'une cible mince par un projectile circulaire en utilisant un modele de fluide elasto-plastique. Comparaison avec des resultats experimentaux
10
Delos-Reyes, Michael A. "Microstructural and mechanisms of cyclic deformation of aluminum single crystals." Thesis, 1995. http://hdl.handle.net/1957/34889.
Full textAbstract:
Aluminum single crystals were cyclically deformed in single-slip at small strain amplitudes
at 77 K to presaturation. The observed mechanical behavior is consistent with other
recent work. The dislocation substructure was analyzed in detail. The structure can be
described as consisting of dense bundles or veins of dislocation dipoles, separated by
lower dislocation density regions where debris is evident. This debris was determined to
be principally relatively short dipole segments. Screw dislocations with the same Burgers
vector span the channels. Dislocations were essentially all of the same Burgers vector.
In-situ cyclic deformation experiments were successfully performed by the X-Y technique
where thin foils are stressed in alternating perpendicular directions. Screw dislocations
span the channel and easily move and reverse direction with shear reversal. Our
experiments indicate that loops frequently expand from the dipole bundles into the
channels and the edge component is absorbed by nearby bundles leaving screw segments
behind. Dipole "flipping" was not observed and these edges are relatively difficult to
mobilize. There is no obvious evidence for internal backstresses that assist plastic
deformation on reversal of the applied shear.<br>Graduation date: 1996
Books on the topic "Strain mechanisms; dislocations"
1
A, Hills D. Solution of Crack Problems: The Distributed Dislocation Technique. Springer Netherlands, 1996.
Find full text
2
Rohde, R. Metallurgical Effects at High Strain Rates. Springer London, Limited, 2012.
Find full text
3
Delos-Reyes, Michael A. Microstructural and mechanisms of cyclic deformation of aluminum single crystals. 1995.
Find full text
4
Hills, D. A., P. A. Kelly, and D. N. Dai. Solution of Crack Problems: The Distributed Dislocation Technique. Springer, 2014.
Find full text
5
Hills, D. A., P. A. Kelly, D. N. Dai, and A. M. Korsunsky. Solution of Crack Problems: The Distributed Dislocation Technique (Solid Mechanics and Its Applications). Springer, 1996.
Find full textBook chapters on the topic "Strain mechanisms; dislocations"
1
Ohmura, Takahito. "Nanomechanical Characterization of Metallic Materials." In The Plaston Concept. Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-7715-1_8.
Full textAbstract:
AbstractMechanical behavior of metallic materials on nanoscale is characterized by using Nanoindentation and Transmission Electron Microscope (TEM) to understand the fundamental plasticity mechanisms associated with microstructural factors including dislocations. The advanced characterization techniques enable us to grasp the behavior on the nanoscale in detail. New knowledges are obtained for the plasticity initiation under the extremely high stress close to the theoretical strength in regions with defect-free matrix and pre-existing defects such as grain boundaries, in-solution elements, and dislocations. The grain boundaries act as an effective dislocation source, the in-solution elements retard a nucleation of dislocation, and the pre-existing dislocations assist a plasticity initiation. The deformation behavior associated with microstructures is also described. The dislocation structure with a certain density was observed right after indentation-induced strain burst, which is so-called “pop-in,” suggesting a dislocation avalanche upon the pop-in. It has been directly observed that the lower mobility screw dislocation causes the higher flow stress in a bcc metal. A remarkable strain softening can be understood by an increase in dislocation density based on conventional physical models. Phase stability for indentation-induced transformation depends on a constraint effect by inter-phase boundary and grain boundary.
2
Sandström, Rolf. "Tertiary Creep." In Basic Modeling and Theory of Creep of Metallic Materials. Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-49507-6_12.
Full textAbstract:
AbstractIn the tertiary stage, the creep rate is continously increasing eventually leading to rupture. Many mechanisms can contribute to the increasing creep rate such as particle coarsening, substructure coarsening, cavitation, changes in the dislocation density and necking. A large number of empirical models exist for the description of tertiary creep and the development of creep damage not least in the context of continuum damage mechanics (CDM). However, there are also basic models. An equation is presented that can describe the whole creep strain versus time curve. Only parameters that are already defined for secondary creep are needed. During the tertiary stage the true applied stress increases rapidly and faster than the counteracting dislocation strength, which is one main reason for the increase in the creep rate during the tertiary stage. Cavitation is of importance, but the cavitation is often local and therefore gives a modest contribution to the creep rate. According Hart’s criterion, necking starts right at the beginning of the tertiary stage. But the necking is not fully developed until close to rupture. This is demonstrated both by uniaxial and multiaxial models and it is also consistent with available experimental data.
3
Zolnikov, Konstantin P., Dmitrij S. Kryzhevich, and Aleksandr V. Korchuganov. "Regularities of Structural Rearrangements in Single- and Bicrystals Near the Contact Zone." In Springer Tracts in Mechanical Engineering. Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-60124-9_14.
Full textAbstract:
AbstractThe chapter is devoted to the analysis of the features of local structural rearrangementsin nanostructured materialsunder shear loadingand nanoindentation. The study was carried out using molecular dynamics-based computer simulation. In particular, we investigated the features of symmetric tilt grain boundary migration in bcc and fcc metals under shear loading. The main emphasis was on identifying atomic mechanisms responsible for the migration of symmetric tilt grain boundaries. We revealed that grain boundaries of this type can move with abnormally high velocities up to several hundred meters per second. The grain boundary velocity depends on the shear rate and grain boundary structure. It is important to note that the migration of grain boundary does not lead to the formation of structural defects. We showed that grain boundary moves in a pronounced jump-like manner as a result of a certain sequence of self-consistent displacements of grain boundary atomic planes and adjacent planes. The number of atomic planes involved in the migration process depends on the structure of the grain boundary. In the case of bcc vanadium, five planes participate in the migration of the Σ5(210)[001] grain boundary, and three planes determine the Σ5(310)[001] grain boundary motion. The Σ5(310)[001] grain boundary in fcc nickel moves as a result of rearrangements of six atomic planes. The stacking order of atomic planes participating in the grain boundary migration can change. A jump-like manner of grain boundary motion may be divided into two stages. The first stage is a long time interval of stress increase during shear loading. The grain boundary is motionless during this period and accumulates elastic strain energy. This is followed by the stage of jump-like grain boundary motion, which results in rapid stress drop. The related study was focused on understanding the atomic rearrangements responsible for the nucleation of plasticity near different crystallographic surfaces of fcc and bcc metals under nanoindentation. We showed that a wedge-shaped region, which consists of atoms with a changed symmetry of the nearest environment, is formed under the indentation of the (001) surface of the copper crystallite. Stacking faults arise in the (111) atomic planes of the contact zone under the indentation of the (011) surface. Their escape on the side free surface leads to a step formation. Indentation of the (111) surface is accompanied by nucleation of partial dislocations in the contact zone subsequent formation of nanotwins. The results of the nanoindentation of bcc iron bicrystal show that the grain boundary prevents the propagation of structural defects nucleated in the contact zone into the neighboring grain.
4
Koyama, Motomichi, Hiroshi Noguchi, and Kaneaki Tsuzaki. "Microstructural Crack Tip Plasticity Controlling Small Fatigue Crack Growth." In The Plaston Concept. Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-7715-1_10.
Full textAbstract:
AbstractIn this chapter, we present a metallurgical–mechanical mechanism-based strategy for the design of fatigue-resistant metals. Specifically, we elucidate the importance of the metallurgical microstructure in a mechanical singular field (crack tip). The fatigue crack growth resistance is controlled through the crack tip “plasticity”, and the effect of the associated microstructure becomes significant when the crack is “small (or short)”. More importantly, the resistance to small crack growth determines a major portion of fatigue life and strength. Therefore, the microstructural crack tip plasticity is a key breakthrough to the development of fatigue-resistant metals. As successful examples of this concept, we introduce the effects of grain refinement, martensitic transformation, strain aging, dislocation planarity enhancement, and microstructure heterogeneity on small fatigue crack growths.
5
Anand, Lallit, Ken Kamrin, and Sanjay Govindjee. "Physical basis of metal plasticity." In Introduction to Mechanics of Solid Materials. Oxford University PressOxford, 2022. http://dx.doi.org/10.1093/oso/9780192866073.003.0012.
Full textAbstract:
Abstract This chapter discusses the polycrystalline aggregate nature of metals and emphasizes that the major mechanism responsible for plastic strain in metallic materials is the motion of line defects—called dislocations—on crystallographic slip planes in crystallographic slip directions within the individual crystals of the aggregate. Schmid’s law, which states that it is necessary for the resolved shear stress on a slip system to reach a critical value for slip to occur, is introduced. The concepts of a glide force acting on a dislocation and the line tension of a dislocation are introduced, and used to discuss the common strengthening mechanisms for a crystal, namely intrinsic lattice resistance, solid solution strengthening, precipitation or dispersion (Orowan) strengthening, and strain-hardening. Yielding of polycrystals is also influenced by the presence of grain-boundaries, and the widely used Hall–Petch relation for the grain-size dependence of the yield strength in polycrystals is discussed.
6
Haidemenopoulos, G. N., and Helen J. Kamoutsi. "Corrosion-Induced Hydrogen Embrittlement in AA2024." In Encyclopedia of Aluminum and Its Alloys. CRC Press, 2019. http://dx.doi.org/10.1201/9781351045636-140000215.
Full textAbstract:
Embrittlement of aluminum alloy 2024 caused by corrosion-induced hydrogen evolution and trapping is discussed in this article. The current literature on corrosion mechanisms, hydrogen trapping, and mechanisms of hydrogen embrittlement is briefly reviewed. Accelerated corrosion tests followed by thermal desorption spectroscopy enabled the identification of hydrogen traps in the microstructure of the material. The nature of these traps was identified by controlled experiments involving solution treatments and plastic deformation prior to corrosion, in order to alter the alloy microstructure. The high-temperature trap is related to the S–CuMgAl2 phase. In the absence of this phase, hydrogen is trapped in vacancies, which liberate hydrogen at even higher temperatures. The lower temperature trap is related to dislocations. The hydrogen trapped at dislocations increases with plastic strain up to a certain strain and then decreases. The hydrogen generated by corrosion diffuses in the interior of the material and establishes a hydrogen-affected zone beneath the corrosion layer. Removal of the corrosion layer leads to complete restoration of yield strength but only partial restoration of ductility. Removal of the corrosion layer and heating at a high enough temperature to activate all traps for hydrogen desorption leads to complete restoration of ductility. A mechanism of corrosion-induced hydrogen embrittlement is suggested.
7
Zhuang, Zhuo, Zhanli Liu, and Yinan Cui. "Strain Gradient Plasticity Theory at the Microscale." In Dislocation Mechanism-Based Crystal Plasticity. Elsevier, 2019. http://dx.doi.org/10.1016/b978-0-12-814591-3.00003-0.
Full text
8
Zhuang, Zhuo, Zhanli Liu, and Yinan Cui. "Strain Rate Effect on Deformation of Single Crystals at Submicron Scale." In Dislocation Mechanism-Based Crystal Plasticity. Elsevier, 2019. http://dx.doi.org/10.1016/b978-0-12-814591-3.00011-x.
Full text
9
Usenko, Dmytro, Iryna Usenko, and Veniamin Soloviev. "THE INFLUENCE OF HETEROGENEOUS MEDIUM MICROSCOPIC PROPERTIES ON PREDICTING MACROSCOPIC PROPERTIES OF MASONRY." In Traditional and innovative scientific research: domestic and foreign experience. Publishing House “Baltija Publishing”, 2024. http://dx.doi.org/10.30525/978-9934-26-436-8-2.
Full textAbstract:
The key aspects of the microscopic description of structurally inhomogeneous media are considered. This makes it possible to evaluate the macroscopic properties of stochastic multicomponent materials using statistical methods and distribution functions of local effective indicators and is important for predicting the behavior of structurally heterogeneous building materials under various conditions. It also allows us to develop new approaches to the creation and use of new materials in the future and their optimization for various applications. Studies of macroscopic and microscopic aspects of dislocations and strains in brick and mortar are described. The influence of these phenomena on the mechanical properties and strength of building structures made of masonry has been studied. Two main types of dislocations are considered - edge and screw, as well as the relationship with macroscopic deformations of the structure of stone materials. Using elasticity theory and brittle fracture mechanics, the mechanical behavior of masonry structures under different loading conditions is analyzed to establish the relationship between stress, strain and strength of masonry. Various ways of calculating the strength of elements and structures are also considered, taking into account the macroscopic and microscopic aspects of dislocations and deformations, and it is proposed to use the results obtained to predict the behavior of masonry structures as a result of the application of a load. The results of the study of the mechanism of dislocation propagation in masonry at the microscopic level are important research in the field of industrial and civil engineering. This will help to better understand the interaction of materials under external loading and optimize masonry installation processes to improve its strength and durability. Research and development in the construction and civil engineering industry is improving the design and efficiency of stone materials. Microscopic and macroscopic aspects of dislocations and deformations in masonry play an important role in increasing the strength and understanding the mechanical properties of building structures. The characteristic dimensions of the component sections of the masonry should be much larger than the molecular kinetic dimensions, but, at the same time, much smaller than the distances at which the averaged state parameters change noticeably. The main aspects of the influence of the microscopic properties of a heterogeneous medium on predicting the macroscopic properties of masonry are considered. Important for understanding and predicting the behavior of structurally inhomogeneous materials under different conditions is the assessment of the macroscopic properties of stochastic multicomponent materials using statistical methods and distribution functions of local effective indicators. Taking this into account makes it possible to develop new approaches to the design and optimization of building materials for various applications. Research into the mechanism of dislocation propagation in masonry provides valuable scientific basis for the development of more efficient installation methods and improved strength properties. This is an important contribution to the construction industry, helping to create stronger, more resilient and longer-lasting building structures. The propagation of dislocations is significantly influenced by the cementitious material, laying methods, and the shape and geometry of masonry elements. The optimization of these factors will reduce the risk of damage and improve the strength characteristics of structures, and, as a result, will lead to the creation of more effective methods for constructing and strengthening buildings and structures. The results described in this monograph allow the development of new materials with improved deformability and load adaptation. This may include the use of composite materials or modification of bonding materials to improve their strength properties. An important aspect is the development of methods for monitoring and diagnosing the condition of masonry. New methods based on the study of dislocations will make it possible to quickly identify damage and take measures to prevent or repair it, which contributes to the safety and stability of buildings.
10
Koman, Bohdan, and Volodymyr Yuzevych. "REGULARITIES OF MACROPLASTIC DEFORMATION OF NARROW-BAND SINGLE CRYSTALS OF CdxHg 1-xTe SOLID SOLUTIONS." In State, trends and prospects of land sciences, environment, physics, mathematics and statistics’ development (1st. ed). Primedia eLaunch LLC, 2020. http://dx.doi.org/10.36074/stplsepmad.ed-1.04.
Full textAbstract:
The regularities of macroplastic deformation of narrow-band semiconductors of HgTe-CdTe solid solution crystals were studied by the uniaxial compression method on a Regel-Dubov relaxometer. The four-stage character of the strain hardening curve “stress-strain” is established. The influence of stoichiometry, load velocity and temperature on the nature of load curves is investigated. From the experiments on the relaxation of mechanical stresses, a thermoactivation analysis of the kinetics of microplastic deformation was performed. Thermoactivation parameters of dislocation motion are estimated. The criteria for performing the Pierrels mechanism of dislocation motion in these crystals are investigated. The influence of light on the macroplastic fluidity of CdxHg1-xTe crystals is described.
Conference papers on the topic "Strain mechanisms; dislocations"
1
Bruemmer, S. M., J. I. Cole, and E. P. Simonen. "Microstructural Evolution, Localized Deformation and Intergranular Stress Corrosion Cracking of Irradiated Stainless Steels." In CORROSION 1997. NACE International, 1997. https://doi.org/10.5006/c1997-97103.
Full textAbstract:
Abstract Microstructural evolution and mechanical behavior of austenitic stainless steels are evaluated for neutron and heavy-ion irradiated materials. Radiation hardening in austenitic stainless steels is shown to result from the evolution of small interstitial dislocation loops during light-water-reactor (LWR) irradiation. The presence of these loops modifies deformation characteristics and prompts a significant increase in yield strength. Available data on stainless steels irradiated under LWR conditions have been analyzed and microstructural characteristics assessed for the critical fluence range (0.5 to 5x1021 n/cm2) where irradiation-assisted stress corrosion cracking susceptibility is observed. Heavy-ion irradiations are used to produce similar defect microstructures enabling the investigation of hardening and deformation mechanisms. Scanning electron, atomic force and transmission electron microscopies are employed to examine tensile test strain rate and temperature effects on deformation characteristics. Dislocation loop microstructures promote inhomogeneous planar deformation within the matrix and regularly spaced steps at the surface during plastic deformation. Twinning is the dominant deformation mechanism at rapid strain rates and at low temperatures, while dislocation channeling is favored at slower strain rates and at higher temperatures. Both mechanisms produce highly localized deformation and large surface slip steps. Channeling, in particular, is capable of creating extensive dislocation pileups and high stresses at internal grain boundaries which may promote intergranular cracking.
2
Soda, Kazuma, Tsuyoshi Sugimoto, and Nozomu Adachi. "Evaluation of the Effect of Strain Accumulation on Dislocations and Grain Growth." In IFHTSE 2024. ASM International, 2024. http://dx.doi.org/10.31399/asm.cp.ifhtse2024p0023.
Full textAbstract:
Abstract It is well known that the maximum prior austenite grain size after carburizing heat treatment is approximately positively correlated with the maximum shear strain in the case of simple deformation of pre process as cold working treatment. On the other hand, it is generally known that the maximum shear strain and the maximum grain size do not correspond when complex cold working is performed, but the reason of these phenomena is not well known. Then, it is necessary to investigate the relationship between the applied strain during cold working with multiple steps and prior austenite grain size after heat treatment(GG). In this study, we used a processing method called HPT processing, which introduces shear strain by torsion deformation under applying high hydrostatic pressure to the top and bottom of a disk-shaped sample using a die, and investigated how GG changes due to the accumulation of dislocations by focusing on the strain amount | ± Δ ε| given in one pass controlled by a processing path called Cyclic-HPT (c-HPT) (4) and the total strain amount 𝛴| ± Δ ε| given to the sample by the accumulation of one pass. As a result, when finer strain is applied, the grain size does not necessarily become smaller, but rather there are boundary conditions that indicate the positive and negative grain size with respect to the number of strains. Similarly, for the grain size distribution, an increase and decrease in grain size was observed with respect to radial distance, so there are boundary conditions that indicate the positive and negative grain size with respect to distance. From these results, it is believed that this may be the mechanism for grain growth behavior in the case of cold working, which involves complex deformation.
3
Joy, Jobin K., A. Rovinelli, M. Arul Kumar, et al. "Experimental and Numerical Characterization of High Temperature Deformation Behavior of 347H Stainless Steel." In AM-EPRI 2024. ASM International, 2024. http://dx.doi.org/10.31399/asm.cp.am-epri-2024p0099.
Full textAbstract:
Abstract This study investigates how temperature affects the plasticity and thermal creep behavior of 347H stainless steel under uniaxial tension. The research combined experimental testing with advanced computational modeling. Two types of experiments were conducted: uniaxial tensile tests at temperatures from 100°C to 750°C using strain rates of ~10⁻⁴ s⁻¹, and creep tests at temperatures between 600°C and 750°C under various stress levels. These experimental results were used to develop and validate a new integrated mechanistic model that can predict material behavior under any loading condition while accounting for both stress and temperature effects. The model was implemented using a polycrystalline microstructure simulation framework based on elasto-viscoplastic Fast Fourier Transform (EVPFFT). It incorporates three key deformation mechanisms: thermally activated dislocation glide, dislocation climb, and vacancy diffusional creep. The model accounts for internal stress distribution within single crystals and considers how precipitates and solute atoms (both interstitial and substitutional) affect dislocation movement. After validation against experimental data, the model was used to generate Ashby-Weertman deformation mechanism maps for 347H steel, providing new insights into how microstructure influences the activation of different creep mechanisms.
4
Jones, Denny A. "Evidence for Localized Surface Plasticity During Stress Corrosion Cracking." In CORROSION 1995. NACE International, 1995. https://doi.org/10.5006/c1995-95169.
Full textAbstract:
Abstract Creep prior to stress corrosion cracking (SCC) has been frequently observed. Externally imposed anodic dissolution currents increase creep rates of pure metals and alloys in environments that do not cause SCC. Creep prior to SCC may result from anodic currents at active film rupture sites caused by coupling to surrounding noble passive surfaces. Several investigators have recently shown a correlation between creep rate and time to failure by SCC, implying that mechanisms of creep and cracking may be related. Recent thin-film diffusion experiments have shown evidence of vacancy formation at anodically dissolving copper surfaces. Anodically generated vacancies may increase creep by stimulating dislocation climb, as does elevated temperature during thermal creep or by attraction to dislocation cores. This paper reviews this and other information leading to a proposed SCC mechanism describing anodic attenuation of strain hardening, localized surface plasticity (LSP), crack initiation, and crack-tip embrittlement by anodic dissolution at film rupture sites.
5
Leinonen, H., T. Saario, and H. Hänninen. "Prediction of Stress Corrosion Cracking Susceptibility of Nitrogen Alloyed Stainless Steels in 50% CaCl2 Solution." In CORROSION 1997. NACE International, 1997. https://doi.org/10.5006/c1997-97189.
Full textAbstract:
Abstract Stress corrosion cracking (SCC) susceptibility of austenitic Type AISI 304L, AISI 316L stainless steels and nitrogen alloyed Type AISI 301 steels in 50% CaCl2 solution at 373 K (100°C) under open-circuit potential and cathodic polarization conditions was studied using a constant load test method. The electrical properties of the surface films formed were monitored as a function of time and potential by means of the Contact Electric Resistance (CER) method. The steady state strain rate (ε˙ss) obtained from the corrosion elongation curve (elongation vs. time curve) showed a linear dependence on time to failure (tf). This means that ε˙ss can be applied as a parameter for prediction of tf. Based on creep measurements in a non-corrosive environment and studied solution, the influence of environment on ε˙ss showed more than fivefold increase in the creep rate, which is a clear indication of the role of creep in SCC mechanism. This environmentally enhanced creep was found in the presence of high resistance passive film on the surface. Nitrogen alloying was found to enhance clearly the passivation. A new model is used to explain and describe the observed phenomena of SCC. The rate determining step in cracking is the generation of vacancies by selective dissolution. The effect of electrochemical polarization on creep is due to a change in the vacancy flux through the oxide film to the metal. Cathodic polarization resulted in decreasing strain rate by reducing the corrosion rate and suppressing the generation of vacancies, which made strain localization more difficult. Vacancies generated by corrosion are first consumed by dislocations which enhances creep, but later agglomeration of vacancies leads under applied stress finally to cleavage-like SCC.
6
Chai, Guocai, Ping Liu, and Johan Frodigh. "Influence of Temperature on the Strain Controlled Fatigue Behaviour of Alloy 690 Tube Material." In 12th International Conference on Nuclear Engineering. ASMEDC, 2004. http://dx.doi.org/10.1115/icone12-49262.
Full textAbstract:
Strain controlled fatigue tests for hot-extruded tube material of Alloy 690 (Sandvik Sanicro 69) have been performed at room temperature (RT) and at elevated temperature (204°C). The influences of temperature on the cyclic deformation behaviour and the fatigue life have been investigated. The influence of temperature on the fatigue life is relatively small in the temperature range investigated. However, the fatigue behaviour at elevated temperature is quite different from that at RT. A second cyclic strain hardening was observed at 204°C. The possible mechanisms have been investigated using transmission electron microscopy. Besides dislocation mechanism, the interactions between moving dislocations and stacking faults and between interstitial atoms and moving dislocations could also contribute to this secondary cyclic strain hardening. The formation of micro-twins during cyclic loading at 204°C and its influence on the cyclic stress-strain response were also discussed. Temperature affects both fatigue crack initiation and propagation behaviour. Increase in temperature promotes duplex slipping process, which causes the formation of striation.
7
Misra, A., H. Kung, D. Hammon, R. G. Hoagland, and M. Nastasi. "Damage Mechanisms in Nanolayered Metallic Composites." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32395.
Full textAbstract:
The strengths of metallic multilayers, composed of alternating layers of soft metals such as Cu and Nb, approach the theoretical limit of material strength when the bilayer periods are on the order of a few nanometers. We have investigated the damage mechanisms in these ultra-high strength nanolayered composite materials subjected to monotonic deformation. Large strain plastic deformation such as room temperature rolling does not lead to any dislocation cell structure formation within the layers indicating that the deformation and dislocation storage mechanisms in nanostructured materials are completely different from the bulk. In bulk metals, dislocation pile-ups lead to heterogeneous slip, but in nano-materials, deformation by single dislocations on closely spaced glide planes results in more homogeneously distributed slip. The implications of the high tensile strengths and homogeneous slip on the fatigue properties of nanolayered materials are also discussed.
8
Do, Hyelim, Changgong Kim, and Kathryn H. Matlack. "Influence of Microstructure and Strain Hardening Rate on Acoustic Nonlinearity Parameter in Stainless Steel 316L during Tensile Loading." In ASNT Research Symposium 2023. The American Society for Nondestructive Testing Inc., 2023. http://dx.doi.org/10.32548/rs.2023.036.
Full textAbstract:
The accumulation of dislocations, which are atomic defects in materials subjected to plastic deformation, can cause structural failures. Early detection of such dislocation-related damage is essential to prevent these failures. The acoustic nonlinearity parameter β has been shown to be sensitive to the nonlinearity of dislocation motions, and prior research has shown a relationship between β and dislocation parameters in various damage mechanisms. While most work thus far reports that β generally increases with increased plastic deformation, recent research showed that β can decrease during monotonic tensile loading in stainless steel 316L characterized by in situ nonlinear ultrasonic measurements. The objective of this research is to examine the correlation between the decrease of β with plastic strain as reported in this recent study, and the initial microstructure and strain hardening rate. The initial microstructure, characterized with electron backscatter diffraction (EBSD), shows an increase in dislocation density and a reduction of grain area, which can possibly result in a decrease in β. Further, it is shown that the decrease rate of β monotonically decreases with hardening rate, providing a evidence that the decrease in β may relate to the shift from planar slip to wavy slip. These results help interpret the underlying mechanisms for the decrease in β during tensile loading.
9
Msolli, S., R. N. Raoelison, and Z. Q. Zhang. "A Physics Based Model for Ultrahigh Strain Rates in Cold Spray." In ITSC2022. DVS Media GmbH, 2022. http://dx.doi.org/10.31399/asm.cp.itsc2022p0383.
Full textAbstract:
Abstract Thermal spray technology keeps attracting several industries in both the manufacturing and repair sectors, thanks to its practicability and its reasonable processing time. Moreover, different kinds of materials can be successfully deposited to form coatings with potential excellent thermo-electro-mechanical properties. The resultant coating microstructure is completely different from the wrought powder material before the deposition process. In the case of metallic materials, the thermomechanical characteristics are quite dependent on the deposition conditions monitored from the spraying setup. One can mention gas temperature, impact velocity and angle, material combination, surface state, particles size, etc. Hence, one major factor which influences the final coating microstructural state is kinetic energy. In fact, in such processes where high velocity deposition is observed, intense grain refinement and sharp increase of the dislocation density are an outcome that is tightly related to high temperature and severe plastic deformation. Prediction of the mechanical properties of the produced coating is usually carried out using phenomenological models that describe very well the relationship between stress and strain under different conditions of temperature and strain rates. Most of these models fail, however, to describe the effect of the deformation mechanisms observed at ultra-high strain rates such as the viscous drag regime of dislocations or further the weak shock load regime, scenarios commonly observed in such processes. In the present paper, we present an enhanced physics-based model to describe the stress strengthening of metals upon impact and associated microstructure changes. We show that the model can accurately represent the desired effect of the dislocation drag. Modelling of the impact of a single copper particle onto a copper substrate is carried out to show the capability of the model to predict grain refinement and dislocation network modification.
10
Fragomeni, James M. "Mechanical Strength Modeling of Particle Strengthened Nickel-Aluminum Alloys Strengthened by Intermetallic γ′ (Ni3Al) Precipitates". У ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0629.
Full textAbstract:
Abstract A Nickel-Aluminum alloy strengthened by γ′ (Ni3Al) intermetallic ordered coherent precipitates with a small misfit strain was used a demonstration material to develop a model to predict strengthening behavior during plastic deformation as a consequence of the γ′ particles acting as obstacles to the dislocations and thus impeding their glide motion through the alloy. It was determined that the two most dominate strengthening mechanisms in the Ni-Al system were order hardening when the particles were smaller than the critical looping radius, and Orowan strengthening when the particles were larger than the looping radius. In the overaged condition when the particles are large in size, the dislocations bypass and loop the particles by the Orowan mechanism. In the underaged to peak aged conditions where the particles are usually smaller than the looping radius, the dislocations shear the precipitates during deformation. The total polycrystalline yield strength included contributions from the intrinsic lattice strength, the solid solution strengthening, grain size strengthening, and particle strengthening which included the order hardening and Orowan strengthening contributions. The total mechanical yield strength for a Ni-6.27wt.%A1 alloy was predicted for the peak-aged condition based on the theory for order strengthening and was found to be in good agreement with the experimental peak-strength data for Ni-6.27A1.
Reports on the topic "Strain mechanisms; dislocations"
1
Hirth, J. P., M. Rhee, H. M. Zhib, and T. D. de la Rubia. 3D dislocation dynamics: stress-strain behavior and hardening mechanisms in FCC and BCC metals. Office of Scientific and Technical Information (OSTI), 1999. http://dx.doi.org/10.2172/12206.
Full text