Dissertations / Theses: 'Laminated'

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Patrick, David G. "Laminated structures for sports mouthguards." Thesis, University of Sheffield, 2005. http://etheses.whiterose.ac.uk/6068/.

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The aims and objectives of this study are to examine the role of mouthguards and the materials that are used for their manufacture, the heating process they undergo during manufacture and how the lamination of different materials into a multi-layered system to form a composite structure may affect the impact absorbing capabilities. The effect of heat on pEVA during the manufacturing process was investigated using an instrumented dropweight impact testing rig and a polariscope to observe internal stress as it was felt that the physical properties of the material could be adversely affected by this part of the process. Laminated structures, using several different materials, (pEVA, PMMA, silicone rubber, synthetic wax, modelling clay, soft denture lining material and a semi-solid synthetic rubber) were tested as it was felt that the lamination of different materials with a range of physical properties would exhibit less deformation and transmit less of the impact energy. To ascertain how a mouthguard may react during an impact event by simulation tests in the impact test rig. Methods: For the heat treatment of pEVA a furnace was used to heat the test material to near its' glass transition temperature (Tg) of 84'C ±3 'C. The material was brought up to Tg and held at that point for 10 minutes. The specimens were then removed from the furnace and allowed to cool to room temperature. Heat treated and non-heat treated samples were placed in a polariscope to observe stress within the material. Dropweight impact tests were conducted on all samples using an instrumented impact testing rig. All samples were circularly clamped and force-time and displacement-time plots obtained. The samples were placed again in the polariscope and any changes in stress were noted. To observe the processing effects of the manufacturing procedure five mouthguards were made on the same cast and were brought to various stages of completion. Different 'lay-ups' of pEVA along with laminations and sandwiches of pEVA, PMMA, silicone rubber, synthetic wax, modelling clay, semi-solid synthetic rubber and denture soft lining were also tested using the dropweight impact tester. For the impact simulation tests samples of 50mm. diameter were placed on top of a PMMA substrate, that was clamped in the impact rig, to see how the test sample would protect the substrate during impact. Results: The Peak Impact Force (PIF) of heat treated pEVA was lower (PIF<140N) than that of untreated pEVA (PIF=160N). The displacement of the heat treated sample during impact increased by 66%, (untreated pEVA>18mm centre displacement, heat treated pEVA >30mm centre displacement). Digital photographic images from the polariscope show that the heat treatment of pEVA virtually eliminates stress and following impact the amount of stress, seen photoelastically, was also reduced. Images of material in the polariscope also indicate that the finishing techniques employed during the manufacturing process have a direct effect on the stress distribution within the mouthguard. A 5mm laminated structure of pEVA, PMMA and silicone rubber was able to absorb more impact energy (PIF = 275N) and exhibited less deformation (1.4mm) than that of a monolithic structure of 5mrn heat treated pEVA (PIF <140N, displacement >30mm). Simulation tests showed that the 5mm. thick pEVA protected the PMMA better (PIF = 325, displacement 6.8mm) than the Imm pEVA (PIF = 340, displacement 7.7mm). Conclusions: The mouthguard forming process has a direct effect on the internal stresses of pEVA and therefore its physical response. When pEVA is laminated with PMMA and silicone rubber the impact absorbing capabilities are better than a monolithic structure of pEVA. Mouthguards for use in contact sports, therefore, should incorporate a laminated section of pEVA, PMMA and silicone rubber. Simulation tests show that 5mm thick samples protect a substrate more effectively than I- 4mm test samples.

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Hassani, Abolfazl. "Bitumin laminated reinforced concrete pavements." Thesis, University of Westminster, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305266.

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Jeong, Han Koo. "Reliability of laminated composite plates." Thesis, University of Southampton, 1999. https://eprints.soton.ac.uk/21869/.

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This thesis deals with reliability analysis of laminated composite plates subjected to transverse lateral pressure loads. Input parameters to strengths of the plates such as applied transverse lateral pressure loads, elastic moduli, geometric and ultimate strength values of the plates are treated as basic design variables, and specific probability distributions are applied to them to take into account the variability nature of these basic design variables. Based on the statistical information on the basic design variables, these variables are pseudo-randomly generated in accordance with the corresponding probability distributions by using statistical sampling techniques. Generated random values of the basic design variables corresponding to the applied loads, elastic moduli and geometric values are substituted into various laminated plate theories which can accommodate different lamination schemes and boundary conditions to assess the probabilistic strengths of the plates. The limit state equations are developed by using maximum stress, maximum strain, Tsai-Hill, Tsai-Wu, Hoffman and Azzi-Tsai-Hill failure criteria. Calculated probabilistic plate strengths and generated random values of the ultimate strength basic design variables of the plates are substituted into the developed limit state equations to define the failure or survival state of the plates. In solving the limit state equations, structural reliability techniques are adopted and evolved appropriately for the reliability analysis of the plates. Developed reliability analysing algorithms are applied to laminated plates from experiment to check its validity. Finally, the EUROCOMP Design Code is compared with the developed reliability analysis procedures by applying the both approaches to the strengths of laminated plates.

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Bloomfield, Mark William. "Efficient optimization of laminated composites." Thesis, University of Bristol, 2010. http://hdl.handle.net/1983/716153ce-1826-4c80-b7fa-369a29f45a9e.

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Zhai, Junyi. "Magnetoelectric laminated composites and devices." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/26310.

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Since the turn of the millennium, giant magnetoelectric (ME) effects have been found in laminated composites of piezoelectric and magnetostrictive layers. Compared to ME single phase and two phase particulate composites, laminated composites have much higher ME coefficients and are also readily fabricated. In this thesis, I have investigated ME effect in laminated composites including materials, structures, fundamental properties and devices. Giant permeability Metglas was incorporated in ME laminates. The piezomagnetic coefficient of the Metglas is larger than that of widely used magnetostrictive materials, such as Terfenol-D or nickel ferrite. The experimental results show that Metglas based ME laminates have giant ME voltage coefficients and small required DC magnetic biases. Besides, the laminates have a good directional dependence of the magnetic field: it can only sense the magnetic field along its longitudinal direction. Symmetric bimorph and differential mode magnetoelectric laminates have been designed to reject (decrease) thermal and vibration noise sources, respectively. The mechanism for the noise cancellation capability is that the laminate operates in a bending (or longitudinal) mode, whereas the noise is contained in the other mode. The ME susceptibility (αme) is the fundamental property that describes the coupling between the polarization and magnetization of a ME media. It is a complex quantity ( ). I discuss the relationship of the ME susceptibility between the magnetic permeability, dielectric permittivity of the materials, and the widely used ME voltage coefficient. The shape of the magnetic layer has a large impact on the giant permeability due to shape demagnetization effects. A long, thin and narrow shape increases the ME voltage coefficient and decreases the required optimum DC bias. The resonance frequency of Terfenol-D/PZT laminates can be continuously tuned by magnetic field over a wide range. This large tunability is due to the large magnetostriction of Terfenol-D. It results in a dramatic increase in the bandwidth over which devices might take advantage of the resonance enhanced ME coefficient. Four device applications have also been studied based on the giant ME effect of laminate composites. (i) ME laminates offer much potential for low-frequency (10⁻² to 10³ Hz) detection of minute magnetic fields (10-12Tesla or below) in a passive mode of operation. With a wrapped active coil, the Metglas/PZT laminates are also capable of detecting changes of 0.8 nano-Tesla in DC magnetic fields without an applied DC bias. (ii) A geomagnetic field sensor is shown to have high sensitivity to variations in Earth's field of HDC=0.8nano-Tesla. It could offer potential applications in global positioning. (iii) Under electro-mechanical resonance drive conditions, ME laminates have been shown to have a high gyration effect. These findings indicate the potential existence of a fifth fundamental network element. (iv) A multimodal system has been developed for simultaneously harvesting mechanical vibration and magnetic energies. Ph. D.

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Buck, Dietrich. "Mechanics of Cross-Laminated Timber." Licentiate thesis, Luleå tekniska universitet, Träteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-68729.

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Increasing awareness of sustainable building materials has led to interest in enhancing the structural performance of engineered wood products. Wood is a sustainable, renewable material, and the increasing use of wood in construction contributes to its sustainability. Multi-layer wooden panels are one type of engineered wood product used in construction. There are various techniques to assemble multi-layer wooden panels into prefabricated, load-bearing construction elements. Assembly techniques considered in the earliest stages of this research work were laminating, nailing, stapling, screwing, stress laminating, doweling, dovetailing, and wood welding. Cross-laminated timber (CLT) was found to offer some advantages over these other techniques. It is cost-effective, not patented, offers freedom of choice regarding the visibility of surfaces, provides the possibility of using different timber quality in the same panel at different points of its thickness, and is the most well-established assembly technique currently used in the industrial market. Building upon that foundational work, the operational capabilities of CLT were further evaluated by creating panels with different layer orientations. The mechanical properties of CLT panels constructed with layers angled in an alternative configuration produced on a modified industrial CLT production line were evaluated. Timber lamellae were adhesively bonded in a single-step press procedure to form CLT panels. Transverse layers were laid at a 45° angle instead of the conventional 90° angle with respect to the longitudinal layers’ 0° angle. Tests were carried out on 40 five-layered CLT panels, each with either a ±45° or a 90° configuration. Half of these panels were evaluated under bending: out-of-plane loading was applied in the principal orientation of the panels via four-point bending. The other twenty were evaluated under compression: an in-plane uniaxial compressive loading was applied in the principal orientation of the panels. Quasi-static loading conditions were used for both in- and out-of-plane testing to determine the extent to which the load-bearing capacity of such panels could be enhanced under the current load case. Modified CLT showed higher stiffness, strength, and fifth-percentile characteristics, values that indicate the load-bearing capacity of these panels as a construction material. Failure modes under in- and out-of-plane loading for each panel type were also assessed. Data from out-of-plane loading were further analysed. A non-contact full-field measurement and analysis technique based on digital image correlation (DIC) was utilised for analysis at global and local scales. DIC evaluation of 100 CLT layers showed that a considerable part of the stiffness of conventional CLT is reduced by the shear resistance of its transverse layers. The presence of heterogeneous features, such as knots, has the desirable effect of reducing the propagation of shear fraction along the layers. These results call into question the current grading criteria in the CLT standard. It is suggested that the lower timber grading limit be adjusted for increased value-yield. The overall experimental results suggest the use of CLT panels with a ±45°-layered configuration for construction. They also motivate the use of alternatively angled layered panels for more construction design freedom, especially in areas that demand shear resistance. In addition, the design possibility that such 45°-configured CLT can carry a given load while using less material than conventional CLT suggests the potential to use such panels in a wider range of structural applications. The results of test production revealed that 45°-configured CLT can be industrially produced without using more material than is required for construction of conventional 90°-configured panels. Based on these results, CLT should be further explored as a suitable product for use in more wooden-panel construction. External cooperation: Martinson Group AB and Research Institutes of Sweden (RISE)

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Uzhan, Tevfik. "Experimental Analysis Of Curved Laminated Beam." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612114/index.pdf.

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ABSTRACT EXPERIMENTAL ANALYSIS OF CURVED LAMINATED GLASS BEAM Uzhan, Tevfik M.S., Department of Engineering Sciences Supervisor: Prof. Dr. M. Z&uuml lf&uuml ASik May 2010, 33 Pages In this thesis, experimental studies are carried out on curved laminated glass beams to form a database for the scientists who may like to test their mathematical models. Beams which are only free to rotate and constrained in radial direction at both ends are tested to make the data available for further calculations. Test setup is prepared to minimize error that could occur due to test setup and data readings. Material testing machine and 4 channel data collecting machine are used to measure the signals at the strain gauges located over the glass beam. Within the range of force applied to the specimens, laminated curved beam shows linear behavior without any fracture. Data collected from the specimens are in conformance with each other. Results obtained from experiments are compared with the results obtained from the mathematical model developed by ASik and Dural (2006). As it is observed from the graphs presented, experimental results from the tests and numerical results from the mathematical model are in good agreement.

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Chan, Yiu Mo Patton. "Laminated beam theory based on homogenization." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0022/MQ50485.pdf.

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Yttergren, Rose-Marie. "Mechanical properties of laminated ceramic composites /." Stockholm : Tekniska högsk, 1999. http://www.lib.kth.se/abs99/ytte0910.pdf.

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Shokrieh, Mahmood M. (Mahmood Mehrdad). "Failure of laminated composite pinned connections." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60608.

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In this investigation the behavior of pin-loaded composite plates is studied analytically. A progressive damage model is presented which is capable of predicting the three different mechanisms of failure: bearing, shearout, and net tension. The model consists of three major parts: stress analysis, and material property degradation rules. Based on the model a computer code is developed. The computer code is capable of assessing damage, evaluating residual strength, and predicting ultimate strength of pin-loaded composite plates. Predicted results are compared with available experimental data. Excellent agreement between the predicted and the experimental data was found. The computer code is used to study geometric parameters that influence joint strength. Such studies are useful in designing mechanical fastened joints using advanced composites.

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Snook, J. R. M. "Adhesion mechanisms of polymer laminated steel." Thesis, Swansea University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639081.

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Polymer laminated steel is increasingly popular in the packaging industry as a competitor to lacquered steel and as a product in its own right. It does however have many benefits over lacquering such as the ability to coat before processing and absence of harmful emissions. One key requirement for such materials is good adhesion between polymer and steel. This work examines the bonding of polymer film to steel substrates in material where the adhesion is relatively good. A test method was developed which produces quantitative results for the strength of this adhesion. It was shown that this method was reproducible and differentiated between good and excellent adhesion. From the results obtained using this test method the effect of substrate and film variations were investigated using a combination of tin and chrome coated steel and polyethylene terephthalate (PET) and polypropylene (PP) polymer films. For the tin substrate it was found that the surface finish affected the adhesion of PET but there was less if any effect on PP adhesion. This was thought to be down to the failure mechanism that occurred in the PET being interfacial whereas for the PP the failure occurred within the polymer and so was not affected so much by surface characteristics. This was confirmed using surface analysis techniques. Chrome coated steel samples were also tested but results from these were less conclusive.

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Timarci, Taner. "Vibrations of composite laminated cylindrical shells." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283227.

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Naskar, Susmita. "Spatial variability characterisation of laminated composites." Thesis, University of Aberdeen, 2018. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=239036.

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Advanced lightweight structural materials like composites are being increasingly utilized in various engineering applications due to high specific strength and stiffness with tailorable properties. Even though composites have the advantage of modulating a large number of design parameters to achieve various application-specific requirements, this concurrently brings the challenge of dealing with inevitable uncertainties during manufacturing and service-life conditions. This dissertation focuses on practically relevant modelling of random spatial variability coupled with the influence of damage to quantify the effect of source-uncertainties following an efficient surrogate based framework. Layer-wise random variable based approach and the random field based approaches of uncertainty modelling are investigated to quantify the stochastic dynamics and stability characteristics of in a probabilistic multi-scale framework. A novel concept of stochastic representative volume element is proposed to consider the spatially varying structural attributes effectively. A physically relevant random field based modelling approach with correlated material properties is adopted based on the Karhunen-Loève expansion. To understand the relative influences, sensitivity of the stochastic input parameters are analyzed for the global structural responses of composite laminates considering micro and macro mechanical properties separately. Besides the conventional sources of uncertainty in material and structural properties, another source of uncertainty is considered in the form of noise. Besides probabilistic analysis, this dissertation proposes a fuzzy representative volume element based approach for modelling spatial variability in non-probabilistic analysis for the cases where statistical distributions of the stochastic input parameters are not available. The results reveal that stochasticity affects the system performance significantly. A notable difference in the global stochastic behaviour is identified depending upon the adopted uncertainty modeling approach. Thus, it is imperative to appropriately model the sourceuncertainties during the analysis and design process. The dissertation provides comprehensive insights on the effect of source-uncertainties on composites following an efficient, yet practically relevant modelling approach.

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Park, Joonsang 1969. "Point sources in cylindrically laminated rods." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/46136.

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Maddison, Eleanor Jane. "Seasonally laminated late Quaternary Antarctic sediments." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56054/.

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Quaternary diatom-rich laminated sediments, found in Antarctic inner shelf depressions, contain high-resolution records of climate change. Diatom assemblages and sediment fabric of four laminated intervals were examined with a scanning electron microscope (using backscattered and secondary electron imagery) and light microscope in this study. Deglacial Palmer Deep laminated sediments (western Antarctic Peninsula) are composed of alternating biogenic diatom ooze and diatom-bearing terrigenous laminae. These laminae are interpreted as spring and summer signals respectively, with negligible winter deposition. Sub-seasonal species specific sub-laminae are observed repeatedly through the summer laminae. Tidal cycles, high storm intensities and / or intrusion of Circumpolar Deep Water onto the continental shelf create variation in shelf waters, enhancing species specific productivity through the summer. Post-glacial Mertz Ninnis Trough laminated sediments (East Antarctic Margin) are composed of five lamina and one sub-lamina types. During deposition the Mertz Glacier Polynya was active and Adelie Land Bottom Water formation was strong. Mid-Holocene Mertz Ninnis Trough laminated sediments are composed of five lamina types. Sea ice cover and sea ice formation was reduced relative to post-glacial times. The Mertz Glacier Polynya was not as active as in the post-glacial and Adelie Land Bottom Water formation was lower. Late-Holocene Durmont d'Urville Trough laminated sediments (East Antarctic Margin) are composed of eight lamina and one sub-lamina types. Sea ice cover was extensive and persistent in the late-Holocene. Warmer periods occurred during the transition from mid-Holocene Climatic Optimum to cooler late-Holocene climatic conditions. The types of lamina and sub-lamina formed in all four laminated intervals are controlled by seasonal sea ice cover, nutrient levels and light levels, which are in turn influenced by climate and oceanography. The Western Antarctic Peninsula and East Antarctic Margin laminated sediments give an insight into oceanographic responses to climatic change and variation through the Quaternary around the Antarctic margin.

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Del, Linz Paolo. "Blast resistance of laminated glass facades." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25145.

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The aim of this thesis is to improve the understanding of the behaviour of Polyvinyl Butyral (PVB) laminated annealed glass façade panels subjected to blast loading. A full scale blast test was performed. During this, deflection and strain data were collected employing digital image correlation techniques (DIC). Local reaction forces were measured using several pairs of strain gauges on the support. The full field deflection and strain data obtained were in line with those observed in historical tests. The strain gauge data available showed that the reaction forces varied along the edge, with higher values being reached at the quarter length gauge locations. The results from this test and from other historical experiments were used to calculate the reaction forces along the entire perimeter of the glass pane. The results showed that the forces reach an early peak before the glass failure, and then rise gradually approaching a plateau at high central deflections. To explain the specific form of this force time history, the detailed behaviour of the laminated material after the glass skins failed was studied. Existing experimental data was employed to fit a material model to the PVB material. Two Prony series models with different hyperelastic springs and a model employing a full finite deformation viscoelastic law derivation were employed. It was found that the finite deformation viscoelastic model could represent the material's behaviour more accurately and fully include its rate dependency. One of the PVB models was employed to study the delamination between the glass and the membrane. Delamination energies were found for different speeds of deformation, and these parameters were employed to study the delamination of samples presenting different crack arrangements. The results showed that these had only a limited influence on the behaviour of the composite.

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Simelane, Philemon Sphiwe. "Thermal buckling of laminated composite plates." Thesis, Peninsula Technikon, 1998. http://hdl.handle.net/20.500.11838/1240.

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Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, 1998 However, studies were also conducted for the buckling of composite laminates involving temperature distribution. Chen and Chen (1991) studied thermal buckling of laminated plates under uniform and nonuniform temperature distribution using the eight-node Serendipity finite element. Mathew, Singh and Rao (1992) investigated thermal buckling of antisymmetric cross-ply composite laminates with a onedimensional furite element having two nodes and six degrees of freedom. Chandrashekhara (1992) accounted for transverse shear flexibility by using the thermo-elastic version of the first-order shear deformation theory. This will also be the case in this report. Literature on buckling and laminated composites abounds. Brush and Aimroth (1975) published a book on Buckling of Bars, Plates, and Shells, while Bushnell (1985) surveyed the Methods and Modes of Behaviour in Static Collapse. The foundation for the study of composite materials was based on the references [8], [10], [15] and [18]. The use of the Finite Element Method to analyse the buckling behaviour of laminated structures comes from references [I], [4]. [I2]. [16], [24] and [32]. Reference [14] provided the basis for the formulation of the variation of the governing equations. Most of the ideas in this report are based on these publications and references. Chapter I of this report introduces the concept of a composite. the formation of a composite and a brief overview of the elements of a composite material. This chapter also presents the concept of buckling that will form the basis of the development of this project. At the end of this chapter the choice of the element that is used in this study is justified. Chapter 2 provides the fundamentals of elasticity that relate to the deformation of a loaded body. In this Chapter the stresses and strains are defined and the temperature terms are introduced. In Chapter 3 the Mindlin plate theory is presented with a view to laying the foundation for the analysis of laminated plates, and as a starting point in the formulation of thermal buckling behaviour of laminated plates. In Chapter 4 the elements of a composite material are discussed and the constitutive equations of a laminated composite plate are built. Also the idea of lamination is introduced and the various simplifications that can be introduced as a result of lamination are discussed. The non-linear equilibrium equations and the stability analysis of a composite plate are formulated in Chapter 5 using the conventional anal}1ical method. The resulting equations justify the use of the Finite Element Method as introduced in Chapter 6 and it is the method by which the governing equations will be solved in ABAQUS computer analysis. The results for various computer runs are presented for a normal plate, a plate with a square hole, and the plate ""ith a circular cut-out in Chapter 7. Also in chapter 7 a comparison is made between the laminate "ith a central hole and a normal plate to study the effect of a cut-out on a critical buckling temperature. Appendices A deals the transverse shear in plates, and Appendix B deals with the transformation of the laminate elastic constants form the principal material direction to the general Cartesian co-ordinates. Also in Appendix B the laminate stiffness matrices and these matrices are briefly evaluated analytically. Appendix C is about the governing equations of laminated composites, while Appendix D gives a full representation of the abbreviated finite element equations of Chapter 6. Appendix E presents the list of ABAQUS input files that were used in the computer simulation of Chapter 7.

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Tiwari, Nachiketa. "Secondary Buckling of Laminated Composite Plates." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/37789.

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The postbuckling load carrying capacity of composite plates offers immense potential to their applications for loads exceeding their primary buckling load. However, such an efficient and economical usage of these plates can be reliable only if the nonlinear postbuckling behavior of these plates, which includes a good understanding of secondary buckling, is understood thoroughly. The present investigation is an attempt to understand secondary buckling of almost square composite clamped-simply supported plates, both unstiffened as well as stiffened, in some detail. With the help of the finite element method, a large number of numerical studies have been conducted to understand the secondary buckling characteristics. The sensitivity of these characteristics to variations in boundary conditions, lamination sequence, imperfections, and stiffener geometry has been considered. It has been found that the occurrence of secondary buckling in clamped-simply supported plates under uniform end shortening critically depends on the intensity of restrictions imposed on the inplane normal displacements along the unloaded simply supported edges of the plate. These restrictions could be due to the actual boundary conditions at these edges, or due to the presence of stiffeners along these edges. It has also been found that the presence of imperfections significantly delays the event of secondary buckling. Finally, it has been found that changes in lamination sequence of the plate alter its secondary buckling characteristics in ways that are, in general, quantitative in nature. The numerical investigations were followed by a limited number of experiments involving the testing of unstiffened as well as stiffened composite plates with the intent of augmenting the confidence in the numerical predictions made. Three different lamination sequences were considered during the testing phase of this investigation. It was found that the agreement between experimental data and numerical predictions was quite good. The occurrence of secondary buckling followed the predictions closely. Ph. D.

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Chillara, Venkata Siva Chaithanya. "Multifunctional Laminated Composites for Morphing Structures." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524104865278235.

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Moorthy, Jayashree. "Dynamic instability of composite laminated plates." Thesis, Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/52090.

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Dynamic instability in a laminated composite plate is studied using the finite element technique. The governing equations are derived based on the first order shear deformation theory with a linear strain-displacement relationship. The regions of instability for the resulting set of coupled Mathieu equations are obtained using a method of simultaneous diagonalization. Boundary frequencies generated using a first subdeterminant approximation to the infinite determinant are compared with those obtained by using the more accurate second subdeterminant as well as with frequencies from an analytical solution. These values are verified by checking the nature of responses near the boundaries between stability and instability. Results are presented for plates with different laminations, boundary conditions, thicknesses, number of layers, etc. Some unstable regions for a damped plate are also shown. Results from the first order plate theory are compared with those from a higher order shear deformation theory. Master of Science

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Turesson, Jonas. "Diagonal compression of Cross-Laminated Timber." Thesis, Luleå tekniska universitet, Träteknologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-59699.

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Twelve blocks of Cross Laminated Timber (CLT) were built, tested and simulated. Three types of blocks with different laminate directions in the middle/second layers were used: 0/30/0, 0/45/0 and 0/90/0. Simulations with three-dimensional quadratic orthotropic linear elastic finite elements were conducted. The goal was to compare tested in-plane shear stiffnesses for CLT blocks made from Norway Spruce (Picea abies) boards of C24 quality with a finite element (FEM) simulated block stiffness. Three-layer CLT were studied with block dimensions of 600 x 600 x 45 mm. The first and last layer laminate directions were assumed to be 0○. The middle layer laminate directions were 30○, 45○ and 90○. A 1 mm gap was assumed between the side edges. The glued contact surfaces were assumed to be perfectly glued with rigid glue in the simulations. In the practically tested blocks a PVAc D2 classified glue was used. All blocks were simulated and tested in the same loading arrangement as the practical test set-up. The blocks were compressed in the diagonal direction. Blocks of 0/30/0 and 0/45/0 were compressed twice, once over each diagonal. The 0/90/0 blocks were compressed over one diagonal. A total of 19 practical compression tests was performed; in all cases, the displacements were measured in the force- and orthogonal direction. The stiffest loading case, measured in the force direction, was the loading arrangement 0/45/0-A. The weakest loading case, measured in the force direction, was the loading arrangement 0/30/0-B. The same result could be concluded from the FEM simulations. The calculated stiffness in the loading direction was between 1.21 – 1.87 times larger than the measured stiffness. The models pressed in the “weakest” direction gave the largest difference between the simulated and measured stiffness.

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Liu, Shao-Chun. "Residual stress characterization for laminated composites." [Florida] : State University System of Florida, 1999. http://etd.fcla.edu/etd/uf/1999/amp7373/liu.pdf.

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Thesis (Ph. D.)--University of Florida, 1999. Title from first page of PDF file. Document formatted into pages; contains xi, 158 p.; also contains graphics. Vita. Includes bibliographical references (p. 152-157).

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De, Genua Francesca. "Engineered Alumina / Silicon Carbide Laminated Composites." Doctoral thesis, Università degli studi di Trento, 2014. https://hdl.handle.net/11572/368173.

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High-melting temperature oxides, carbides and nitrides are superior in hardness and strength to metals, especially in severe conditions. However, the extensive use of such ceramics in structural engineering applications often encountered critical problems due to their lack of damage tolerance and to the limited mechanical reliability. Several ceramic composites and, in particular, laminated structures have been developed in recent years to enhance strength, toughness and to improve flaw tolerance. Significant strength increase and improved mechanical reliability, in terms of Weibull modulus or minimum threshold failure stress, can be achieved by the engineering of the critical surface region in the ceramic component. Such effect can be realized by using a laminated composite structure with tailored sub-surface insertion of layers with different composition. Such laminate is able to develop, upon co-sintering, a spatial variation of residual stress with maximum compression at specific depth from the surface due to the differences in thermal expansion coefficient of the constituting layers. In the present work silicon carbide has been selected as second phase to graduate the thermal expansion coefficient of alumina due to its relatively low specific density that could allow the production of lighter components with improved mechanical performance, also for high temperature applications. Ceramic laminates with strong interfaces composed of Al2O3/SiC composite layers were produced by pressureless sintering or Spark Plasma Sintering (SPS) of green layers stacks prepared by tape casting water-based suspensions. Monolithic composites containing up to 30 vol% silicon carbide were fabricated and thoroughly characterized. Five engineered ceramic laminates with peculiar layers combination that is able to promote the stable growth of surface defects before final failure were also designed and produced. By changing the composition of the stacked laminae and the architecture of the laminate, tailored residual stress profile and T-curve were generated after co-sintering and successive cooling in each multilayer. The results of the mechanical characterization show that the engineered laminates are sensibly stronger than parent monolithic composite ceramic and exhibit surface damage insensitivity, according to the design. Such shielding effect is especially observed when macroscopic cracks are introduced by high load Vickers indentations. Some designed multilayers exhibit reduced strength scatter and higher Weibull modulus, which implies superior mechanical reliability. Fractographic observations on fracture surfaces of the engineered laminates show a graceful crack propagation within the surface layers in residual compressive stress which can be attributed to the stable growth of superficial cracks before final failure as it is predicted by the apparent fracture toughness curve. Such fracture behaviour is considered to be responsible for the peculiar surface damage insensitivity and the improved mechanical performance.

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De, Genua Francesca. "Engineered Alumina / Silicon Carbide Laminated Composites." Doctoral thesis, University of Trento, 2014. http://eprints-phd.biblio.unitn.it/1219/1/PhD_Thesis_DE_GENUA_FRANCESCA.pdf.

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High-melting temperature oxides, carbides and nitrides are superior in hardness and strength to metals, especially in severe conditions. However, the extensive use of such ceramics in structural engineering applications often encountered critical problems due to their lack of damage tolerance and to the limited mechanical reliability. Several ceramic composites and, in particular, laminated structures have been developed in recent years to enhance strength, toughness and to improve flaw tolerance. Significant strength increase and improved mechanical reliability, in terms of Weibull modulus or minimum threshold failure stress, can be achieved by the engineering of the critical surface region in the ceramic component. Such effect can be realized by using a laminated composite structure with tailored sub-surface insertion of layers with different composition. Such laminate is able to develop, upon co-sintering, a spatial variation of residual stress with maximum compression at specific depth from the surface due to the differences in thermal expansion coefficient of the constituting layers. In the present work silicon carbide has been selected as second phase to graduate the thermal expansion coefficient of alumina due to its relatively low specific density that could allow the production of lighter components with improved mechanical performance, also for high temperature applications. Ceramic laminates with strong interfaces composed of Al2O3/SiC composite layers were produced by pressureless sintering or Spark Plasma Sintering (SPS) of green layers stacks prepared by tape casting water-based suspensions. Monolithic composites containing up to 30 vol% silicon carbide were fabricated and thoroughly characterized. Five engineered ceramic laminates with peculiar layers combination that is able to promote the stable growth of surface defects before final failure were also designed and produced. By changing the composition of the stacked laminae and the architecture of the laminate, tailored residual stress profile and T-curve were generated after co-sintering and successive cooling in each multilayer. The results of the mechanical characterization show that the engineered laminates are sensibly stronger than parent monolithic composite ceramic and exhibit surface damage insensitivity, according to the design. Such shielding effect is especially observed when macroscopic cracks are introduced by high load Vickers indentations. Some designed multilayers exhibit reduced strength scatter and higher Weibull modulus, which implies superior mechanical reliability. Fractographic observations on fracture surfaces of the engineered laminates show a graceful crack propagation within the surface layers in residual compressive stress which can be attributed to the stable growth of superficial cracks before final failure as it is predicted by the apparent fracture toughness curve. Such fracture behaviour is considered to be responsible for the peculiar surface damage insensitivity and the improved mechanical performance.

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ALEMAN, ROMAN AUGUSTO ARCINIEGA. "STABILITY ANALYSIS OF LAMINATED COMPOSITE CYLINDRICAL SHELLS AND PANELSSTABILITY ANALYSIS OF LAMINATED COMPOSITE CYLINDRICAL SHELLS AND PANELS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1946@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR Este trabalho apresenta um estudo do comportamento não- linear e instabilidade de cascas e painéis cilíndricos laminados de materiais compósitos. Com esta finalidade é desenvolvida uma formulação de alta ordem de deformação cisalhante que leva en conta estes efeitos nas relações deformação-deslocamento. O comportamento da casca é descrito por uma consistente teoria não-linear para cascas laminadas que considera pequenas deformações e rotações moderadas e incorpora automaticamente o efeito das deformações cisalhantes. O modelo de bifurcação clássico é utilizado para estudar a estabilidade da casca compósita. O comportamento pós-crítico é examinado a partir de uma solução modal obtida com técnicas de perturbação. Em ambos os casos aplica-se o método de Rayleigh-Ritz para discretizar o sistema de equações diferenciais de equilíbrio em um sistema de equações algébricas. O método de Newton-Raphson é empregado na resolução das equações não- lineares de equilíbrio do caminho pós-crítico e na obtenção do caminho fundamental da estrutura imperfeita. A implementação numérica (em álgebra simbólica) é feita utilizando a linguagem de programação Maple V release 3. É então desenvolvido um estudo paramétrico com o objetivo de determinar a influência dos parâmetros geométricos e das características próprias do laminado (número de lâminas e orientação das fibras) na resposta crítica e pós-crítica da casca compósita para dois tipos de carregamento, a saber: pressão lateral e compressão axial. É analisado, também, o grau de sensibilidade às imperfeições geométricas destas estruturas. São apresentadas comparações dos resultados teóricos aqui obtidos com outros existentes na literatura com o objetivo de demonstrar a confiabilidade da formulação e metodologia numérica aqui desenvolvidas. The purpose of the present work is to study the non-linear behaviour and instability of laminated composite cylindrical shells and panels under axial and pressure loading. The analysis is performed within a refined non- linear theory for composite laminated shells incorporating the effects of transverse shear and the geometric imperfections. The classical bifurcation theory is used to analyze the critical behavior of the shell. To examine the post-critical behavior of the shell, a modal solution based on the basic ideas of Koiter`s theory is deduced and the Rayleigh-Ritz method together with the Newton-Raphson strategy are used to solve the non-linear equilibrium problem and plot either the post-critical path or the non- linear equilibrium path of the imperfect shell. The analytical and numerical procedures were performed by the use of the symbolic algebra package Maple V release 3. The influence played by the geometrical parametrs of the shell and physical parameters of the composite laminate, such as stacking sequences and fiber orientation in each lamina, on the critical and post-critical behavior of the shell is examined and a series of conclusions are outlined. The imperfection sensitivity of these shells is also analyzed. Comparisons of the present results with those obtained by other theories and experiments are found to be satisfactory and show the validity of the present methodology. Este trabajo presenta un estudio de la inestabilidad y comportamiento no lineal y la inestabilidad de cortezas y paneles cilíndricos laminados de materiales compuestos. Con esta finalidad se desarrolla una formulación de alta orden de deformación cisallante que considera estos hechos en las relaciones deformación desplazamiento. EL comportamiento de la corteza se describe a través de una consistente teoría no lineal para cascas laminadas. Esta teoría considera pequeñas deformaciones y rotaciones moderadas e incorpora automáticamente las deformaciones cisallantes. El modelo de bifurcación clásico se utiliza para estudiar la estabilidad de la corteza. El comportamiento poscrítico se examina a partir de una solución modal obtenida con técnicas de perturbación. En ambos casos se aplica el método de Rayleigh Ritz para discretizar el sistema de ecuaciones diferenciales de equilibrio en un sistema de ecuaciones algébraicas. El método de Newton Raphson es utilizado en la resolución de las ecuaciones no lineares de equilibrio del camino postcrítico y en la obtención del camino fundamental de la extructura imperfecta. La implementación numérica (en álgebra simbólica) se realiza utilizando el lenguaje de programación Maple V release 3. Con el objetivo de determinar la influencia de los parámetros geométricos y de las características proprias del laminado en la respuesta crítica y postcrítica de la casca compósita, se realiza un estudio paramétrico para para dos tipos de carga: presión lateral y compresión axial. Se analiza también, el grado de sensibilidad a las imperfeiciones geométricas de estas extructuras. Finalmente, y con el objetivo de demostrar la confiabilidad de la formulación y la metodología numérica aqui desarrolladas, se comparan los resultados teóricos obtenidos con los reportados en la literatura.

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32

Pelegri, Assimina A. "Delamination growth behavior in cross-ply composites under compressive cyclic (fatigue) loading." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12004.

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Haynes, Robert Andrew. "Hygrothermally stable laminated composites with optimal coupling." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34671.

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This work begins by establishing the necessary and sufficient conditions for hygrothermal stability of composite laminates. An investigation is performed into the range of coupling achievable from within all hygrothermally stable families. The minimum number of plies required to create an asymmetric hygrothermally stable stacking sequence is found to be five. Next, a rigorous and general approach for determining designs corresponding to optimal levels of coupling is established through the use of a constrained optimization procedure. Couplings investigated include extension-twist, bend-twist, extension-bend, shear-twist, and anticlastic. For extension-twist and bend-twist coupling, specimens from five- through ten-ply laminates are manufactured and tested to demonstrate hygrothermal stability and achievable levels of coupling. Nonlinear models and finite element analysis are developed, and predictions are verified through comparison with test results. Sensitivity analyses are performed to demonstrate the robustness of the hygrothermal stability and couplings to deviations in ply angle, typical of manufacturing tolerances. Comparisons are made with current state-of-the-art suboptimal layups, and significant increases in coupling over previously known levels are demonstrated.

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Feng, Jie. "On the viscoelastic response of laminated composites." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ45219.pdf.

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35

Iqbal, K. "Mechanics of laminated bi-stable tubular structures." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604943.

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Bi-stable silt tubes made of laminated composites are novel deployable structures with two different stable configurations. In the first configuration the tubes are straight and strain-free. In the second configuration they are tightly rolled-up and subject to high levels of strain. To achieve this configuration, they have to climb up and across an energy barrier until a potential energy well is reached from where they can only jump out with some external help. These tubes can be used for large deployable structures as deployment actuators in a manner similar to a STEM. But, unlike the STEM, they do not need any drum to roll upon. The key to this bi-stable behaviour is a particular type of composite construction, invented by Daton-Lovett (1996), in which stiff fibres are arranged to ±α to the longitudinal axis, where α is about 45o. The fibre layout is anti-symmetric with respect to the mid-surface of the tube, to avoid twisting the tube when it is rolled up. Analytical models are presented to predict the radius of curvature in second stable configuration. These models assume linear-elastic behaviour of the material and derive the total strain energy expression, which includes the bending strain energy, membrane strain energy and coupled strain energy, within the tube. These models clearly show that the strain energy increases as we move away from the zero energy point, which corresponds to the extended, strain free configuration. This increase is particularly sensitive to the variations in the longitudinal curvature of the tube and less so to the variations in the transverse curvature. Another analytical model is presented to predict the edge deformations in coiled configuration using an anisotropic closed cylinder. It is shown that linear shell theory with appropriate adjustments works very well for laminated slit tubes.

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Sun, Liecheng. "ANALYTICAL STRIP METHOD TO ANTISYMMETRIC LAMINATED PLATES." UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/715.

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An Analytical Strip Method (ASM) for the analysis of stiffened and non-stiffened antisymmetric laminated composite plates is derived by considering the bending-extension coupling effect for bending, free vibration and buckling. A system of three equations of equilibrium, governing the general response of arbitrarily laminated composite plates, is reduced to a single eighth order partial differential equation in terms of a displacement function. The displacement function is solved in a single series form to determine the displacement, fundamental frequency, and buckling load of antisymmetric cross-ply and angle-ply laminated composite plates. The solution is applicable to rectangular plates with two opposite edges simply supported, while the other edges are simply supported, clamped, free, beam supported, or any combinations of these boundary conditions. This method overcomes the limitations of other analytical methods (Navier’s and Lévy’s), and provides an alternative to numerical, semi-numerical, and approximate methods of analysis. Numerical examples of bending, free vibration, and buckling of antisymmetric laminated composite plates are presented in tabular and graphical form. Whenever possible, the results of the present study are compared with those published in the literature and/or ANSYS solutions. The comparison firmly establishes that this method could be used for the analysis of antisymmetric laminated composite plates. Future research needs are identified for the aspects that have not been reached by the present study and others.

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Parkyn, A. T. "Residual stresses in laminated thermoplastic matrix composites." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234355.

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Tippetts, Trevor 1977. "Modeling impact damage in laminated composite plates." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/82782.

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Westermark, Lovisa. "Mechanical Characterization and Simulations of Laminated Pressboard." Thesis, KTH, Hållfasthetslära (Inst.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176033.

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Pressboard is a cellulose-based material, which is used in transformers as insulation as well as for providing structural support. The micro-structure of pressboard consists of networks of cellulose fibers, which has good mechanical properties as well as exceptional electrical insulation properties. Paper materials, such as pressboard, have anisotropic material properties due to events in the manufacturing process. Pressboard has been investigated earlier, but here laminated pressboard is studied. The objective of this study was to characterize the mechanical properties by means of experimental characterization and finite element simulations. The mechanical responses of laminated pressboard were studied under three- and four-pointbending (flexure) tests. In addition to the flexure tests, shear tests were performed on samples with asymmetric double notches under uniaxial tension. The objective of these tests was to calibrate model parameters related to through-thickness shear deformation. The finite element simulations of the shear tests captured the initial behavior of the experiments. At increasing strain levels there was a discrepancy between the experimental results and the results from the simulations. This can be explained by the evolution of damage in the material under the experiments and damage was not included in the present model. The simulations of the bending tests had a weaker response compared to the experiments for both three- and four-point bending. This could be explained by the penetration of glue into the pressboard, which makes the overall response of the laminated material stiffer.

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Ferreira, Rafael Thiago Luiz. "Contributions in the optimization of laminated composites." Instituto Tecnológico de Aeronáutica, 2013. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=2760.

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This work verses about contributions in the optimization of laminated fiber reinforced composites. At first, it is presented a new solution concept to Discrete Material Optimization (DMO) problems based on Sequential Approximate Optimization (SAO) techniques, employing new compliance approximations in terms of intermediate variables which are explicit functions of the DMO weights. The proposed methodology improves significantly the quality of the approximations and consequently the general convergence characteristics of several DMO compliance minimization (stiffness maximization) problems. Then, it is presented a Hierarchical Optimization scheme for laminated composite structures, considering simultaneous design of macroscopic (structural) and microscopic (material) levels. The macroscopic level takes into account orientations and fiber volume fractions of unidirectional composite layers. The microscopic level considers the cross-sectional size and shape of the reinforcement fibers, assuming them elliptical. Both levels are coupled and the objective is to minimize compliance under a total fiber volume fraction constraint. It is shown that changes in the shape of the fibers permit to increase structural stiffness. An assessment of microstructural stresses is also included and shows the fibers'; shape influence on layers'; stress concentrations.

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Sambasivam, Shamala. "Thermoelastic stress analysis of laminated composite materials." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/72144/.

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In this work thermoelastic stress analysis (TSA) is used to obtain quantitative stress/ strain data from a variety of multi-directional laminated composites. In order to in- terpret the thermoelastic signal correctly the source of the thermoeleastic response has been investigated in detail. In this thesis four possible routines to extract quantitative stress/strain information from thermoelastic data have been explored. A set of carefully selected glass/epoxy composite specimens with designated stacking sequences provided a scheme to identify the source and nature of the thermoelastic response. All of the material properties of the composite laminate were obtained experimentally, to aid an accurate assessment of each routine. The variation in the stress experienced by the laminate in the surface resin layer and ply by ply there after leads to large variations in the temperature change through the thickness. The thermoelastic measurements from dierent laminates revealed a local non-adiabatic condition within the layered medium. Therefore, the implication of applied loading frequency on the heat conduction properties of the laminates was studied. Based on the experimental observation from a representa- tive specimen, numerical models have been developed to understand the nature of the heat transfer in the glass/ epoxy material considered in this work. An analysis of the eect of holes in a variety of laminated components is presented to provide stress concen- tration factors (SCF's) based on TSA data. The conventional, orthotropic surface ply model most often used for thermoelastic stress analysis of composite material is revisited in order to elucidate the invariant nature of the equation. This is an important base for the analysis of structures which are better notated in coordinate system other than Cartesian, or as ratio of thermoelastic measurements in two dierent coordinate systems. The nature of the thermoelastic response in the presence of the in-plane stress gradient is investigated with the aid of numerical and analytical models. An introductory work for quantifying the SCF's around pin-loaded holes in laminated composite based on TSA measurements is also presented. The work presented in this thesis provides a step forward in the application of TSA to the composite materials in a quantitative manner.

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Stamatopoulos, Ioannis D. "Analytical techniques for modelling the laminated waveguide." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/844108/.

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This thesis is focused on a study on the dispersion formulation of the recently appeared ''laminated waveguide". In this framework a new method for the analysis of a wide variety of microwave components like posts, circular junctions or corners in rectangular waveguides is developed. This method can be used to model the posts in the laminated waveguide geometry and this was the main motivation of the present work. The method gives the impedance or admittance matrix of the microwave component by applying discrimination between the localised and accessible modes on the indirect mode matching (IMM) formulation. In all cases the method proved to be fast, very accurate and easy to implement. The application of the IMM technique to the dispersion formulation of the laminated waveguide is undertaken by implementing the Transverse Resonance Method. It is the first time that effort is paid, so that every possible polarisation of both bounded and unbounded modes is considered. In the process a new analytic solution is given for the modelling of the transverse bifurcation. Its significance relies on the the fact that the method of moments is not to be used in the analysis and thus its overall speed is increased. The total procedure is expected to be straightforward and flexible.

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Khan, Arafat Islam. "Progressive Failure Analysis of Laminated Composite Structures." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64389.

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Laminated composite structures have started to play a very significant role in today's aircraft industry. The application of composite materials has now gone beyond the borders of aircraft design and has entered into such fields as automotive, athletics and recreational equipment, etc. The light weight and high specific strength of composite material helps design vehicles with higher fuel efficiency and longevity. In order to understand the influence of design parameters related to the use of composite materials in these applications, a proper study of the laminated composite structures requires a complete failure analysis, which includes both initiation and propagation of damage. In this work a progressive failure methodology is developed and implemented in the commercial Finite Element software package, Abaqus. Out of the numerous failure criteria available in the literature to study damage initiation and propagation in unidirectional fiber reinforced composites, Puck and Schurmann's failure criteria have been chosen due to their ability to predict results close to those observed experimentally. Key features of the Puck and Schurmann's failure criteria for three-dimensional deformations of unidirectional fiber reinforced composites have been summarized. Failure modes in the matrix and the fiber are considered separately. The failure criteria are simplified for plane stress deformations. Whereas the failure plane can be analytically identified for plane stress deformations, a numerical search algorithm is needed for three-dimensional problems. Subsequent to the initiation of matrix failure, elastic moduli are degraded and values of these degradation parameters and fracture plane angles are found by using a Continuum Damage Mechanics (CDM) approach. It is found that the assumption that the material response remains transversely isotropic even after the matrix failure has initiated requires the degradation of the transverse Poisson's ratio. The Puck and Schurmann's failure criteria and the material degradation process have been implemented as a User Defined Field (USDFLD) subroutine in Abaqus. The implementation has been verified by analytically computing results for simple loadings and comparing them with predictions from using the USDFLD in Abaqus. Subsequently, both two- and three-dimensional problems of more realistic geometries and loadings have been analyzed and computed results compared with either experimental findings or results available in the literature. Major contributions of the work include identifying the degradation parameter for the transverse Poisson's ratio in terms of the matrix degradation parameter for the matrix failure in compression, development of the USDFLD based on Puck and Schurmann's failure criteria, implementing the USDFLD in the commercial finite element software, Abaqus, and verifying that results computing using the USDFLD for various laminates and loadings agree with those from either the analytical solution of the problem or those available in the literature. Ph. D.

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Tang, Bruce S. "Lamb wave propagation in laminated composite plates." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/80194.

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Low frequency Lamb waves in composite laminates were investigated theoretically and experimentally. To have a general solution for Lamb wave propagation in multilayered composite laminates is not practical due to a large number of boundary conditions needed to be satisfied at the interlaminar interfaces. Various approximate theories have been proposed to model low frequency Lamb wave propagation in composite laminates. In the present study, an approximate solution was derived from an elementary shear deformation plate theory and was shown to work well in the low frequency, long wavelength region. A simple method, similar in configuration to the acousto-ultrasonic technique, was used to measure Lamb wave phase velocities. Low frequency Lamb waves, usually in the range of 10 kHz to 1 MHz, were generated. Dispersion curves of the lowest symmetric Lamb mode and the lowest antisymmetric Lamb mode were obtained. The experimental data were compared with the results obtained from the approximate solution for the lowest Lamb modes in the low frequency, long wavelength region for a unidirectional laminate, a symmetric cross-ply laminate, a symmetric quasi-isotropic laminate and an aluminum plate. There is good correlation between the data and the results obtained from the approximate solution, which suggests that the lowest Lamb modes are modeled adequately by the present theory in these cases. This experimental procedure of measuring phase velocities can be used to characterize laminated composite plates with and without damage since each material and stacking sequence gives distinct lowest symmetric and antisymmetric curves. Stiffness reduction of composite laminates caused by damage can be related to the change in Lamb wave propagation speed. Damage in the form of transverse cracks in the 90° plies of a [90/90/90/0], graphite/epoxy laminate reduced the phase velocities of the Lamb modes. The lowest antisymmetric mode is sensitive to stiffness reduction in composite plates. Consequently, axial stiffness reduction in [0/45/0/45/0/45], and [0]₁₂ woven graphite/polyimide composite laminates was monitored by the lowest antisymmetric Lamb mode. Ph. D.

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45

Chang, Jin-Der. "Theory of thick, laminated composite shallow shells /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487779914824542.

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Torneport, Matilda. "Industrial Requirements for Cross-Laminated Timber Manufacturing." Thesis, Linnéuniversitetet, Institutionen för skog och träteknik (SOT), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-104924.

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Wood is a valuable sustainable material that meets the requirements for structural application. Cross-laminated timber (CLT) is a wood-based product that is mainly used in the building industry. Due to the rapid global market increase, a number of new CLT plants are emerging worldwide and thereby a need for standardisation is more than ever. There is no existing harmonised standard for CLT and it means a diversity between manufacturers, CLT products and its layup, which may in turn affects the properties of available CLT in the market. Therefore, this study was performed through literature study and internet-based interviews from five manufacturer in Sweden and Central Europe, to provide more information regarding the industrial requirements for CLT production. Three specific objectives of this study were: (1) wood and adhesive types in CLT production, (2) wood strength classes for CLT production, (3) important requirements for CLT producers and existing standards. Literature review and interviews showed that spruce (Picea abies L. Karst.) in combination with polyurethane (PUR) adhesive is the most commonly used materials in Europe for CLT production, which are approved by EN 16351 (2021). Other wood species, e.g., pine, poplar and birch can be used or are already used in a minor extent. Strength classes for lamellas in CLT are often C24, but timbers with lower strength grades are possible. Some manufacturer use combinations of different strength graded timber and in this small scale study different strength graded timber was in generally the biggest diversity between manufactures. Only a few material properties such as modulus of elasticity, modulus of rupture, compression and shear strength are listed in EN 16351 (2021) and EN 338 (2016), as the factors for quality measurements of the CLT products. This study, however, showed that the critical material properties for the most interviewed CLT producers are merely modulus of elasticity and rarely modulus of rupture.

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Harrison, Matthew J. K. "The tribology of laminated magnetic recording heads." Thesis, Aston University, 1999. http://publications.aston.ac.uk/7990/.

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This thesis investigates the mechanisms that lead to pole tip recession (PTR) in laminated magnetic recording heads (also known as "sandwich heads"). These heads provide a platform for the utilisation of advanced soft magnetic thin films in practical recording heads suitable for high frequency helical scan tape recording systems. PTR results from a differential wear of the magnetic pole piece from the tape-bearing surface of the head. It results in a spacing loss of the playback or read signal of 54.6dB per recording wavelength separation of the poles from the tape. PTR depends on the material combination used in the head, on the tape type and the climate - temperature and relative humidity (r.h.). Five head materials were studied: two non-magnetic substrate materials- sintered multi granular CaTi03 and composite CaTi03/ZrTi04/Ti02 and three soft magnetic materials- amorphous CoNbZr, and nanocrystalline FeNbSiN and FeTaN. Single material dummy heads were constructed and their wear rates measured when cycling them in a Hi-8 camcorder against commercially available metal particulate (MP) and metal evaporated (ME) tapes in three different climates: 25°C/20%r.h., 25°C/80%r.h. and 40°C/80%r.h. X-ray photoelectron spectroscopy (XPS) was used to examine changes the head surface chemistry. Atomic force microscopy (AFM) was used to examine changes in head and tape surface topography. PTR versus cycling time of laminated heads of CaTi03/ZrTiO4/Ti02 and FeTaN construction was measured using AFM. The principal wear mechanism observed for all head materials was microabrasion caused by the mating body - the tape surface. The variation in wear rate with climate and tape type was due to a variation in severity in this mechanism, except for tape cycling at 40°C in which gross damage was observed to be occurring to the head surface. Two subsidiary wear mechanisms were found: third body scratching (all materials) and grain pullout (both ceramics and FeNbSiN). No chemical wear was observed, though tribochemical reactions were observed on the metal head surfaces. PTR was found to be caused by two mechanisms - the first differential microabrasion of the metal and substrate materials and which was characterised by a low (~10nm) equilibrium value. The second was by deep ploughing by third body debris particles, thought mainly to be grain pullout particles. This level of PTR caused by this mechanism was often more severe, and of a non-equilibrium nature. It was observed more for ME tape, especially at 40°C/80%r.h. and 25°c/20%r.h. Two other phenomena on the laminated head pole piece were observed and commented upon: staining and ripple texturing.

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48

Gutkin, Renaud. "Understanding and modelling failure of laminated composites." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6066.

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In this thesis, experimental investigations together with analytical and numerical work on the understanding and modelling of failure in laminated composites are presented. Failure of carbon fibre reinforced plastics is investigated using acoustic emission. Signals are collected for various test configurations which give rise to specific failure modes. The signals are then analysed using pattern recognition techniques and the fast Fourier transform. An identi cation of the failure modes with their acoustic signatures is proposed using the fast Fourier transform, which was found to be the most suitable technique. The failure modes in longitudinal compression are then studied using microscopy techniques and finite element modelling. Experimental observations show that failure results from an interaction between shear-driven compressive failure and kinkband formation. Micromechanical finite element analyses are used to explain the experimental observations. The interaction of shear-driven compressive failure and kinking captured by the model is used to explain the variation in characteristics typically measured in failure envelopes for combined longitudinal compression vs. in-plane shear. Based on the experimental and the numerical results, a failure criterion for fibre kinking and splitting is developed and used to predict failure envelopes for combined longitudinal compression vs. in-plane shear. The model correlates well with the numerical predictions and experimental results. The R-curve effect observed in mode I intralaminar matrix crack growth and its specimen-dependence are then investigated. Relationships between crack extension and crack opening displacement are obtained for the Double Cantilever Beam (DCB) and Compact Tension (CT) specimens. Measured R-curves are used with the previous relationships to define a trilinear cohesive law. The cohesive law is implemented in finite element models and the load versus displacement curves predicted for the DCB and CT specimens show that the R-curve effect is numerically well captured.

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Hooper, Paul. "Blast performance of silicone-bonded laminated glass." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6861.

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Blast resistant glazing systems typically use laminated glass to reduce the risk of flying glass debris in an explosion. Laminated glass has a bonded polymer interlayer that retains glass fragments upon fracture. With proper design, the flexibility of the interlayer in laminated glass can offer protection from significantly higher blast loads when compared to an equivalent monolithic pane. This thesis investigates the post-fracture behaviour of laminated glass under blast loading and aims to build the knowledge required to improve design methods for blast resistant glazing. Full-scale open-air blast tests were performed on laminated glass containing a polyvinyl butyral (PVB) interlayer. Test windows ranged in size from 1.5m×1.2m to 3.5m×1.8m and were bonded to robust frames using structural silicone sealant. Blast loads were produced using charge masses of 15 kg to 500 kg (TNT equivalent) and distances of 10m to 30 m. Deflection and shape measurements were obtained using high-speed digital image correlation. Measurements of loading at the joint were also made with strain gauges. The main failure mechanisms observed were the cohesive failure of the bonded silicone joint and tearing of the interlayer. These failure mechanisms were investigated further using a highspeed tensile test machine to reproduce blast loading conditions. Cracked laminated glass samples were loaded in tension at varying rates. Their response was characterised by a rate dependant plateau force which can be used to estimate the maximum load on the glazing joint. Delamination between the PVB and glass was found to play a key role in the laminate response. Thinner PVB and higher strain rates reduced the delamination area, leading to premature tearing of the interlayer. The strength of structural silicone sealant in a blast situation was also investigated. A novel test method was used to determine the bond length required to retain the laminated glass window in a blast event. A nominal strength of not greater than 1.1MPa should be used for design of conventional single-sided silicone joints. A finite element model of the laminated glass response to blast loading was developed using the results of the experimental investigations. The failure predictions of the model were compared against a single-degree-of-freedom (SDOF) model and showed good agreement. Differences in the deflected shape at maximum deflection were seen between the model and those measured in blast testing.

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Moas, Eduardo. "Progressive failure analysis of laminated composite structures." Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10052007-143154/.

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Dissertations / Theses on the topic 'Laminated'

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