Dissertations / Theses on the topic 'Laminated and sandwich composite'
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Zhao, Huyue. "Stress Analysis of Tapered Sandwich Panels with Isotropic or Laminated Composite Facings." Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/ZhaoH2002.pdf.
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Nayak, Ajaya Kumar. "On dynamic analysis of laminated composite and sandwich plates using finite element method." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/43633/.
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Two new multi-layered plate bending elements (DKT/CST and DKT/LST) are developed based on a combination of the three model Discrete Kirchhoff theory (DKT) triangular plate bending element, the three model constant strain triangle (CST) and the six noded linear strain triangle (LST). Both frequency independent and frequency dependent damping of viscoelastic materials are considered. An iterative complex eigensolver is used to compute the natural frequencies and model loss factors. Several bench mark problems are solved using these new multi-layer plate elements. As the plate bending elements previously developed on the basis of Kirchhoff's theory are inadequate for thick plate analysis, several quadrilateral Mindlin plate bending elements are developed to study the behaviour of Mindlin plates. The plate bending elements based on Mindlin theory require shear correction factors in their formulations. Hence two new Co assumed strain finite element formulations of a refined third order theory which does not require shear correction factors, are developed and used to analyse isotropic, orthotropic, and layered anisotropic composite and sandwich plates under free vibration, damping and transient loading conditions. Parametric effects of plate aspect ratio, length to thickness ratio, degree of orthotropy, number of layers and lamination scheme on the natural frequencies (free vibration), model loss factors (damping) and dynamic (transient) responses have been shown. The results presented in this investigation could be useful in better understanding the behaviour of sandwich laminates under dynamic conditions and potentially beneficial for designers of sandwich structures.
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Kilic, Yavuz S. M. Massachusetts Institute of Technology. "Impact and energy absorption of laminated and sandwich composites." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44883.
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Thesis (S.M. in Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 115-131).
Advanced fiber reinforced composites combine high specific strength and stiffness. Advanced composites are currently being introduced into modern U.S. Navy ships to achieve weight savings, maintenance reduction, and signature reduction. These advancements manifest themselves in Naval ships as increases in survivability, payload, range, speed, and weapon systems performance. In this thesis, vinyl ester resin matrix laminates and sandwich composites are emphasized since they are increasingly being used in naval applications. Impact damage of laminated and sandwich composites under low-velocity and high-velocity impact are investigated. Delamination damage is explored in detail since delamination is one of the major failure modes of many advanced composites structures. Delamination initiation loads for various laminates having different stacking sequences are compared. In many laminates containing various stacking sequences, placing the 900 laminae on the outside (as opposed to the inside) will reduce the delamination initiation load under impact. Moreover, an open literature survey of numerous laminated and sandwich composites having different stacking sequences and thicknesses and subjected to low-velocity impact is undertaken. The failure mode, failure load, and displacement at failure of these composites are summarized. Other topics investigated include (1) effects of a composite's constituents on damage susceptibility, (2) post-impact residual characterization and strength, and (3) nondestructive testing techniques. Prediction methods for residual strength are tabulated based on the impact damage type for laminated and sandwich composites. Further, NASA and Boeing compression-after-impact tests are summarized for laminated composites after low-energy impacts.
(cont.) Damage and residual strength are analyzed for epoxy and PEEK resin laminates. An initial sorting for the selection of nondestructive testing methods for specific composite discontinuities is summarized. Extensive presentations of tables and figures are used to summarize the results of the literature surveys on impact resistance and energy absorbing capabilities of composites. Particular attention is given to methods for impact resistance improvement. Impact resistance improvement methods are compared according to increases in interlaminar Mode I and Mode II fracture toughness and in residual strength. These comparisons support data for the selection of impact resistance improvement. Numerous laminates having different lamina orientations are compared to understand the influence of stacking sequence on impact damage resistance and energy absorption capability. Matrix properties are investigated for many laminates and it is noted that higher interlaminar fracture toughness of matrix materials will increase energy absorption capability. The effects of other constituents of a laminate on impact resistance and energy absorbing capability are also summarized. Among the types of composites investigated in this thesis, carbon fiber/PEEK laminates exhibited the highest specific energy absorption. Recommendations for further studies are offered based on these summaries.
by Yavuz Kilic.
S.M.in Naval Architecture and Marine Engineering
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Monge, J. C., J. L. Mantari, and R. A. Arciniega. "Computational semi-analytical method for the 3D elasticity bending solution of laminated composite and sandwich doubly-curved shells." Elsevier Ltd, 2020. http://hdl.handle.net/10757/656405.
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El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado.In this paper, a three-dimensional numerical solution for the bending study of laminated composite doubly-curved shells is presented. The partial differential equations are solved analytically by the Navier summation for the midsurface variables; this method is only valid for shells with constant curvature where boundary conditions are considered simply supported. The partial differential equations present different coefficients, which depend on the thickness coordinates. A semi-analytical solution and the so-called Differential Quadrature Method are used to calculate an approximated derivative of a certain function by a weighted summation of the function evaluated in a certain grin domain. Each layer is discretized by a grid point distribution such as: Chebyshev-Gauss-Lobatto, Legendre, Ding and Uniform. As part of the formulation, the inter-laminar continuity conditions of displacements and transverse shear stresses between the interfaces of two layers are imposed. The proper traction conditions at the top and bottom of the shell due to applied transverse loadings are also considered. The present results are compared with other 3D solutions available in the literature, classical 2D models, Layer-wise models, etc. Comparison of the results show that the present formulation correctly predicts through-the-thickness distributions for stresses and displacements while maintaining a low computational cost.
Consejo Nacional de Ciencia, TecnologÃa e Innovación Tecnológica
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Ghoor, Ismail B. "The response of concave singly curved fibre reinforced moulded sandwich and laminated composite panels to blast loading." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/27811.
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Composite materials are increasingly being used in a wide range of structural applications. These applications range from bicycle frames and building facades to hulls of marine ships. Their popularity is due to the high specific strength and stiffness properties, corrosion resistance, and the ability to tailor their properties to a required application. With the increasing use of composites, there is a need to better understand the material and damage behaviour of these structures. In recent years, the increased frequency of wars and terror attacks have prompted investigations into composite failure processes resulting from air-blast. Most of the research has been focused on flat panels, whereas there is relatively little on curved structures. This dissertation reports on the effect of air-blast loading on concave, singly curved fibre reinforced sandwich and composite panels. Sandwich panels and equivalent mass glass fibre laminates were manufactured and tested. Three types of curvature namely a flat panel (with infinite curvature), a curvature of 1000 mm radius and a curvature of 500 mm radius were produced, to determine the influence of curvature on panel response. The laminates were made from 16 layers of 400 g/m² plain weave glass fibre infused with Prime 20 LV epoxy resin. The sandwich panels consisted of a 15 mm thick Airex C70:75 core sandwiched between the 12 layers of 400 g/m² plain weave glass fibre and infused with Prime 20 LV epoxy resin. This arrangement produced a balanced sandwich panel with 6 layers of glass fibre on the front and back respectively. For all panels, vacuum infusion was used to manufacture in a single shot process. Mechanical properties of samples were tested for consistency in manufacturing. It was found that mechanical properties of the samples tested were consistent with low standard deviations on tensile and flexural strength. The panels were tested in the blast chamber flat the University of Cape Town. Blast specimens were clamped onto a pendulum to facilitate impulse measurement. Discs of plastic explosive, with charge masses ranging from 10 g to 25 g, were detonated. After blast testing, a post-mortem analysis of the damaged panels was conducted. Post-mortem analysis revealed that the failure progression was the same irrespective of curvature for both the sandwich panels and the laminates. Sandwich panels exhibited the following failure progression: delamination, matrix failure, core crushing, core shear, core fragmentation, core penetration and fibre fracture. The laminates displayed the following progression: delamination, matrix failure and fibre fracture. Curved panels exhibited failure initiation at lower charge masses than the flat panels. As the curvature increased, the failure modes initiated at lower charge masses. For example, as the charge mass was increased to 12.5 g the front face sheets of the flat and the 1000 mm radius sandwich panels exhibited fibre fracture, but the 500 mm radius sandwich panel exhibited fibre fracture and rupture through the thickness of the front face sheet. The 500 mm radius laminate exhibited front face failure earlier (15 g) than the 1000 mm radius (22.5 g) and flat panel (20 g). Curved laminates exhibited a favoured delamination pattern along the curved edges of the panel for both 1000 mm and 500 mm radii laminates. As the curvature increased, more delamination was evident on the curved edges. The curved panels displayed more severe damage than flat panels at identical charge masses. Curved sandwich panels experienced through thickness rupture at 20 g charge mass whereas the curved laminates did not exhibit rupture at 25 g charge mass. The flat laminates were the most blast resistant, showing no through-thickness penetration at 25 g (the highest charge mass tested) and initiated failure modes at higher charge masses when compared to the other configurations.
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Ghinet, Sebastian. "Statistical energy analysis of the transmission loss of sandwich and laminate composite structures." Thèse, Université de Sherbrooke, 2005. http://savoirs.usherbrooke.ca/handle/11143/1770.
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The present study emerges from a present industry need for accurate and fast numerical modeling approaches to estimate the vibro-acoustic behaviours of multilayered composite and viscoelastic treatments configurations.The structure is modeled using a wave approach applied to various multilayer configurations such as: symmetrical laminate composite, symmetrical sandwich composite and general symmetrical or unsymmetrical laminate or sandwich composite as well as viscoelastic treatments. Three behavioural modeling approaches are investigated: smeared laminate, discrete layer sandwich and general discrete layer laminate. Smeared laminate approach is devoted to symmetrical laminate composite panels and uses equivalent elastic properties computed by smearing out the layers' properties through the panel's thickness. Discrete layer sandwich approach is devoted to symmetrical sandwich composite panels and uses individual displacement fields for each layer. Classical assumptions of thick skins sandwich panels are adopted. General discrete laminate approach accommodates both laminate and sandwich composite panels of symmetrical or unsymmetrical layout. Individual displacement fields are used for each layer. These three behavioural modeling approaches are applied in the present work to flat and curved panel configurations as well as laminated beams. Dispersion relations are developed for each configuration and solved in a generalized polynomial eigenvalue problem context. These solutions are used in a SEA framework to compute the group velocity, the modal density, the radiation efficiency as well as the resonant and non-resonant contributions to the transmission coefficient. Moreover, the dispersion relations are used to develop general expressions to compute the ring frequency and the critical frequencies. In the context of viscoelastic treatments modeling the mechanical impedance, the input mobility, the deformation energy as well as the equivalent loss factor are computed for several boundary conditions.The presented approaches are successfully validated with experimental results and previously published theories. In addition to their proven accuracy, the proposed approaches are quick and general.
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Shah, Priyal. "Computational Analysis of Elastic Moduli of Covalently Functionalized Carbon Nanomaterials, Infinitesimal Elastostatic Deformations of Doubly Curved Laminated Shells, and Curing of Laminates." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77034.
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We numerically analyze three mechanics problems described below. For each problem, the developed computational model is verified by comparing computed results for example problems with those available in the literature.
Effective utilization of single wall carbon nanotubes (SWCNTs) and single layer graphene sheets (SLGSs) as reinforcements in nanocomposites requires their strong binding with the surrounding matrix. An effective technique to enhance this binding is to functionalize SWCNTs and SLGSs by covalent attachment of appropriate chemical groups. However, this damages their pristine structures that may degrade their mechanical properties. Here, we delineate using molecular mechanics simulations effects of covalent functionalization on elastic moduli of these nanomaterials. It is found that Young's modulus and the shear modulus of an SWCNT (SLGS), respectively, decrease by about 34% (73%) and 43% (42%) when 20% (10%) of carbon atoms are functionalized for each of the four functional groups of different polarities studied.
A shell theory that gives results close to the solution of the corresponding 3-dimensional problem depends upon the shell geometry, applied loads, and initial and boundary conditions. Here, by using a third order shear and normal deformable theory and the finite element method (FEM), we delineate for a doubly curved shell deformed statically with general tractions and subjected to different boundary conditions effects of geometric parameters on in-plane and transverse stretching and bending deformations. These results should help designers decide when to consider effects of these deformation modes for doubly curved shells.
Composite laminates are usually fabricated by curing resin pre-impregnated fiber layers in an autoclave under prescribed temperature and pressure cycles. A challenge is to reduce residual stresses developed during this process and simultaneously minimize the cure cycle time. Here, we use the FEM and a genetic algorithm to find the optimal cycle parameters. It is found that in comparison to the manufacturer's recommended cycle, for a laminate with the span/thickness of 12.5, one optimal cycle reduces residual stresses by 47% and the total cure time from 5 to 4 hours, and another reduces the total cure time to 2 hours and residual stresses by 8%.Ph. D.
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Alanbay, Berkan. "Free Vibrations and Static Deformations of Composite Laminates and Sandwich Plates using Ritz Method." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/103087.
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In this study, Ritz method has been employed to analyze the following problems: free vibrations of plates with curvilinear stiffeners, the lowest 100 frequencies of thick isotropic plates, free vibrations of thick quadrilateral laminates and free vibrations and static deformations of rectangular laminates, and sandwich structures. Admissible functions in the Ritz method are chosen as a product of the classical Jacobi orthogonal polynomials and weight functions that exactly satisfy the prescribed essential boundary conditions while maintaining orthogonality of the admissible functions. For free vibrations of plates with curvilinear stiffeners, made possible by additive manufacturing, both plate and stiffeners are modeled using a first-order shear deformation theory. For the thick isotropic plates and laminates, a third-order
shear and normal deformation theory is used. The accuracy and computational efficiency of formulations are shown through a range of numerical examples involving different boundary conditions and plate thicknesses. The above formulations assume the whole plate as an equivalent single layer. When the material properties of individual layers are close to each other or thickness of the plate is small compared to other dimensions, the equivalent single layer plate (ESL) theories provide accurate solutions for vibrations and static deformations of multilayered structures. If, however, sufficiently large differences in material properties of individual layers such as those in sandwich structure that consists of stiff outer face sheets (e.g., carbon fiber-reinforced epoxy composite) and soft core (e.g., foam) exist, multilayered
structures may exhibit complex kinematic behaviors. Hence, in such case, Cz0 conditions, namely, piecewise continuity of displacements and the interlaminar continuity of transverse stresses must be taken into account. Here, Ritz formulations are extended for ESL and layerwise (LW) Nth-order shear and normal deformation theories to model sandwich structures with various face-to-core stiffness ratios. In the LW theory, the C0 continuity of displacements is satisfied. However, the continuity of transverse stresses is not satisfied in both ESL and LW theories leading to inaccurate transverse stresses. This shortcoming is remedied by using a one-step well-known stress recovery scheme (SRS). Furthermore, analytical solutions of three-dimensional linear elasticity theory for vibrations and static deformations of simply supported sandwich plates are developed and used to investigate the limitations and applicability of ESL and LW plate theories for various face-to-core stiffness ratios. In addition to natural frequency results obtained from ESL and LW theories, the solutions of the corresponding 3-dimensional linearly elastic problems obtained with the commercial finite element method (FEM) software, ABAQUS, are provided. It is found that LW and ESL (even though its higher-order) theories can produce accurate natural frequency results compared to FEM with a considerably lesser number of degrees of freedom.Doctor of Philosophy
In everyday life, plate-like structures find applications such as boards displaying advertisements, signs on shops and panels on automobiles. These structures are typically nailed, welded, or glued to supports at one or more edges. When subjected to disturbances such as wind gusts, plate-like structures vibrate. The frequency (number of cycles per second) of a structure in the absence of an applied external load is called its natural frequency that depends upon plate's geometric dimensions, its material and how it is supported at the edges. If the frequency of an applied disturbance matches one of the natural frequencies of the plate, then it will vibrate violently. To avoid such situations in structural designs, it is important to know the natural frequencies of a plate under different support conditions. One would also expect the plate to be able to support the designed structural load without breaking; hence knowledge of plate's deformations and stresses developed in it is equally important. These require mathematical models that adequately characterize their static and dynamic behavior. Most mathematical models are based on plate theories. Although plates are three-dimensional (3D) objects, their thickness is small as compared to the in-plane dimensions. Thus, they are analyzed as 2D objects using assumptions on the displacement fields and using quantities averaged over the plate thickness. These provide many plate theories, each with its own computational efficiency and fidelity (the degree to which it reproduces behavior of the 3-D object). Hence, a plate theory can be developed to provide accurately a quantity of interest. Some issues are more challenging for low-fidelity plate theories than others. For example, the greater the plate thickness, the higher the fidelity of plate theories required for obtaining accurate natural frequencies and deformations. Another challenging issue arises when a sandwich structure consists of strong face-sheets (e.g., made of carbon fiber-reinforced epoxy composite) and a soft core (e.g., made of foam) embedded between them. Sandwich structures exhibit more complex behavior than monolithic plates. Thus, many widely used plate theories may not provide accurate results for them. Here, we have used different plate theories to solve problems including those for sandwich structures. The governing equations of the plate theories are solved numerically (i.e., they are approximately satisfied) using the Ritz method named after Walter Ritz and weighted Jacobi polynomials. It is shown that these provide accurate solutions and the corresponding numerical algorithms are computationally more economical than the commonly used finite element method. To evaluate the accuracy of a plate theory, we have analytically solved (i.e., the governing equations are satisfied at every point in the problem domain) equations of the 3D theory of linear elasticity. The results presented in this research should help structural designers.
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Taetragool, Unchalisa. "Optimal Parameters for Doubly Curved Sandwich Shells, Composite Laminates, and Atmospheric Plasma Spray Process." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/81978.
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Optimization is a decision making process to solve problems in a number of fields including engineering mechanics. Bio-inspired optimization algorithms, including genetic algorithm (GA), have been studied for many years. There is a large literature on applying the GA to mechanics problems. However, disadvantages of the GA include the high computational cost and the inability to get the global optimal solution that can be found by using a honeybee-inspired optimization algorithm, called the New Nest-Site Selection (NeSS). We use the NeSS to find optimal parameters for three mechanics problems by following the three processes: screening, identifying relationships, and optimization. The screening process identifies significant parameters from a set of input parameters of interest. Then, relationships between the significant input parameters and responses are established. Finally, the optimization process searches for an optimal solution to achieve objectives of a problem.
For the first two problems, we use the NeSS algorithm in conjunction with a third order shear and normal deformable plate theory (TSNDT), the finite element method (FEM), a one-step stress recovery scheme (SRS) and the Tsai-Wu failure criterion to find the stacking sequence of composite laminates and the topology and materials for doubly curved sandwich shells to maximize the first failure load. It is followed by the progressive failure analysis to determine the ultimate failure load. For the sandwich shell, we use the maximum transverse shear stress criterion for delineating failure of the core, and also study simultaneously maximizing the first failure load and minimizing the mass subject to certain constraints. For composite laminates, it is found that the first failure load for an optimally designed stacking sequence exceeds that for the typical [0°/90°]₅ laminate by about 36%. Moreover, the design for the optimal first failure load need not have the maximum ultimate load. For clamped laminates and sandwich shells, the ultimate load is about 50% higher than the first failure load. However, for simply supported edges the ultimate load is generally only about 10% higher than the first failure load.
For the atmospheric spray process, we employ the NeSS algorithm to find optimal values of four process input parameters, namely the argon flow rate, the hydrogen flow rate, the powder feed rate and the current, that result in the desired mean particle temperature and the mean particle velocity when they reach the substrate. These optimal values give the desired mean particle temperature and the mean particle velocity within 5% of their target values.Ph. D.
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Elmushyakhi, Abraham. "In-Plane Fatigue Characterization of Core Joints in Sandwich Composite Structures." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1510678155755824.
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Ho, Qhinhon D. "An Assessment Of The Accuracy Of The Euler-Bernoulli Beam Theory For Calculating Strain and Deflection in Composite Sandwich Beams." ScholarWorks@UNO, 2015. http://scholarworks.uno.edu/td/2084.
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This study focuses on assessing the accuracy of the Euler-Bernoulli beam theory as computational bases to calculate strain and deflection of composite sandwich beam subjected to three-point and four-point bending. Two groups of composite sandwich beams tests results will be used for comparison purposes. Mechanical properties for the laminated skin are provided by researchers from University of Mississippi (Ellen Lackey et al., 2000). Mechanical properties for the balsa wood core are provided by Alcan Baltek Corporation. Appropriate material properties and test geometries are then used in the Euler-Bernoulli-based algorithm in order to generate analytical data for comparison to experimental data provided by researchers from University of New Orleans (UNO, 2005). The resulting single material cross section is then analyzed in the traditional manner using the Euler-Bernoulli beam theory. In general, the Euler-Bernoulli beam theory provides an appropriate analytical approach in predicting flexural behavior of composite sandwich beams.
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Zhang, Yuwu. "Dynamic response of high-performance honeycomb cores and hybrid fibre composite laminates for lightweight sandwich structures." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/53371/.
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Lightweight sandwich structures that are composed of high–performance core and face sheets, have been attracting attention in both civilian and military applications due to their outstanding mechanical properties. Honeycomb cores and fibre reinforced composite face sheets have specific advantages for resisting dynamic impact. For example, honeycomb cores possess higher specific-strength (ratio of strength to relative density) than the other sandwich cores under compression, and carbon fibre composites possess high tensile strength and low density. This thesis focuses on the understanding of the dynamic compressive response of high-performance honeycombs and the ballistic impact resistance of stiff/soft hybrid fibre composite laminate beams. For honeycomb cores, the out-of-plane compressive behaviour of the AlSi10Mg alloy hierarchical honeycombs and commercially available Nomex honeycombs have been experimentally and numerically investigated. Owing to the complex in-plane topology, hierarchical honeycombs were fabricated using the Selective Laser Melting (SLM) technique. The experimental measurement and finite element (FE) calculation indicate that the two hierarchical honeycombs, specifically two-scale and three-scale honeycombs, both offer higher wall compressive strengths than the single-scale honeycombs. With an increase in relative density, the single-scale honeycomb experiences a transition in terms of failure mechanism from local plastic buckling of walls to local damage of the parent material. Alternately, the two-scale and three-scale hierarchical honeycombs all fail with solely parent material damage. The dynamic compressive strength enhancement of the hierarchical honeycombs is dominated by the strain rate sensitivity of the parent material. For Nomex honeycombs, the dynamic failure mode under out-of-plane compression is different from the quasi-static failure mode, i.e. the honeycombs fail due to stubbing of cell walls at the end of specimens under dynamic compression, whereas fail due to local phenolic resin fracture after elastic buckling of the honeycomb wall under quasi-static compression. The dynamic compressive strength of Nomex honeycombs increases linearly, and the strength enhancement is governed by two mechanisms: the strain rate effect of the phenolic resin and inertial stabilization of honeycomb unit cell walls. The inertial stabilization of unit cell walls plays a more significant role in strength enhancement than the strain rate effect of the phenolic resin. In addition, the effect of key parameters such as impact method and initial geometrical imperfections on the compressive responses of honeycombs has also been numerically investigated. For face sheets, the ballistic resistance of the beams hybridizing stiff and soft carbon fibre composites has also been experimentally studied, and these results were compared with those of stiff and soft composite beams with identical areal mass. The failure modes of composite beams under different velocity impacts have been identified to be different. For monolithic beams, the hybrid and soft monolithic beams exhibited similar energy absorption capacity. As for the sandwich beams, the hybrid sandwich beams behaved better in terms of energy absorption than soft sandwich beams at high projectile velocities. Both the hybrid and soft composite beams absorbed more kinetic energy from projectiles than stiff composite beams. The advantages of the stiff/soft hybrid composites can be summarized as follows: (i) the soft composite part survives at low velocity impact; (ii) the stiff composite part of the hybrid monolithic/sandwich beams has a more uniform stress distribution than the stiff monolithic/sandwich beams owing to the buffer effect of the soft composite part. This work identifies the advantages of high performance honeycomb cores as well as fibre composite face sheets. These findings can be used to develop high strength, low weight and multi-functional sandwich structures, thereby widening their applicability to a wider array of fields.
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Sinclair, Gregory Maurice. "The response of singly curved fibre reinforced sandwich and laminate composite panels subjected to localised blast loads." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13328.
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Includes bibliographical references.This report presents results from a study on the response of singly curved fibre reinforced polymer (FRP) sandwich and laminate panels subjected to localised blast loads. The aim of the project was to investigate and compare the blast mitigation potential of each panel type and the influence of curvature on the response. Three radii of curvature were examined for both panel types, namely infinite (flat), 1000mm and 500mm. The FRP laminate panels were designed to consist of 1-5 layers of Eglass fibre reinforced epoxy sheets. The FRP sandwich panels consisted of a PVC foam core with 6 layers of FRP sheets on either side. Vacuum infusion, with the aid of three moulds, was used to manufacture the panels. The average thicknesses and areal densities of the FRP sandwich and laminate panels were 18.7mm and 4.9mm; and 862-8g/1m2 and 8458-g/m2 respectively. Three point quasi-static flexural tests were conducted on FRP sandwich and laminate specimens where the localised compression failure beneath the central loading bar was evident on both types of structures. The presence of the core reduced the damage observed on the back face of the FRP sandwich specimens. Blast tests were conducted on a horizontal ballistic pendulum at the Blast Impact and Survivability Research Unit (BISRU), University of Cape Town. Localised blasts were generated by detonating circular cylinder PE4 plastic explosives, placed at a constant standoff distance of 10mm. The charge mass ranged from 10g to 32.5g across all the panels. The failure modes of the blast loaded panels were identified by a post-test inspection. The failure mode initiation charts for the F RP sandwich panels revealed that failure modes were initially observed on the front face sheet and core material with slight appearance of delamination on the back face sheet. Increasing the charge mass resulted in the rupture of the front face sheet and penetration of the core. Additional failure of the back face sheet was also evident as the charge mass increased. The failure mode initiation charts of the FRP laminate panels exhibited less severe failure modes across a greater charge mass range that eventually lead to complete fibre rupture at higher charge masses. Delamination of the front face sheet of the flat FRP sandwich panels was initially observed in the centre of the panel and spread into the exterior region for increasing charge mass. The failure of the core material initially reduced the delaminated area of the back face sheet, however once the rupture of the front face sheet occurred, the delaminated area of the front face sheet reduced and the delaminated area of the back face sheet increased. This was similar for the curved FRP sandwich panels except that the delaminated area was predominately parallel to the axis of curvature prior to rupture and perpendicular to the axis of curvature subsequent to rupture. Delamination in the flat FRP laminate panels was initially observed in the centre of the panel and along the clamped boundary. Increasing charge mass resulted in the delaminated region spreading across the panel. As with the FRP sandwich panels, the delaminated area of the curved FRP laminate panels was initially observed parallel to the axis of curvature prior to rupture. Debonding of the FRP sandwich panels was initially observed at both of the front and back interfaces. For the front interface, the debonded lengths were observed in the centre and in exterior test area of the panel, but only in exterior test area for the back interface. With the rupture of the front face sheet, the debonded length of the front interface decreased and the back interface increased and spread across the entire test area. The blast rupture threshold of the two panel types were compared in terms of largest charge mass resisted. For each radii category, the FRP laminate panels outperformed the FRP sandwich panels, namely by 5g for the flat panels (25g vs 20g) and 9g for the 1000mm curved panels (27.5g vs 18.5g). However, for the 500mm curved panels the FRP laminate and sandwich panels ruptured at identical charge masses of 27.5g.
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Hussain, Muzzamal. "Couplage procédé / propriétés mécaniques des matériaux sandwiches Métal / Composite hybride à base de tissus en jute." Thesis, Lille, 2021. http://www.theses.fr/2021LILUI006.
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Dans cette étude, les propriétés mécaniques des FML renforcés de jute tissé 3D et hybrides de jute tissé 3D renforcé ont été étudiées. Le renfort tissé 3D à quatre couches a été fabriqué avec du fil de jute en utilisant quatre types de motifs imbriqués, par ex. Orthogonal Through Thickness OTT et Orthogonal Layer to Layer OLL imbriqué. La technique d'infusion sous vide a été utilisée pour la fabrication de FML avec renfort en jute tissé 3D. Après l'optimisation du renforcement tissé 3D, les FML renforcés hybrides ont été développés dans lesquels le tissu tissé OTT 3D a été pris en sandwich entre une peau tissée 2D. Quatre types de fibres différents ont été utilisés pour fabriquer une peau tissée 2D, par ex. jute, aramide, carbone et verre tandis que trois types différents de matrice ont été utilisés, par ex. époxy, PVB et PP. La presse à chaud par compression a été utilisée pour développer des FML hybrides renforcés. L'aluminium utilisé pour fabriquer tous les FML a été anodisé avant d'être utilisé pour la fabrication. Les propriétés adhésives ont été étudiées pour vérifier la qualité du traitement de surface, la liaison métal-composites et l'effet des fibres et de la matrice. Les propriétés monotones et dynamiques ont également été étudiées. Les propriétés adhésives ont été caractérisées à l'aide de tests de pelage en T et de pelage au rouleau flottant. Les propriétés monotones ont été analysées à l'aide d'essais de traction et de flexion. Les performances d'impact à faible vitesse ont été déterminées en utilisant un test d'impact à faible vitesse. Les résultats ont montré que la surface en aluminium anodisé avait une énergie libre de surface élevée, de sorte que le meilleur mouillage de l'aluminium peut être obtenu par anodisation par rapport à d'autres types de préparations de surface. Les résultats de l'analyse du collage ont montré que les propriétés de délaminage étaient principalement influencées par la nature du matériau adhésif plutôt que par le type de structures de renforcement. La nature de la matrice influence également le type de défaillance car avec l'époxy, la défaillance dominante était cohésive tandis qu'avec la matrice thermoplastique, elle s'est transformée en défaillance adhésive et intra-laminaire. La plasticité et la ductilité de la matrice ont plus influencé les propriétés finales que le type de rupture, malgré la rupture cohésive de l'époxy, la matrice thermoplastique avait plus de force de délamination. Les propriétés de traction et de flexion des FML renforcées de jute tissé OTT 3D étaient supérieures à celles des FML renforcées tissées OLL 3D en raison de la fraction de volume de métal plus élevée, ce qui était possible grâce à une construction plus serrée du tissu OTT. Les propriétés de traction et de flexion des composites hybrides renforcés et des FML ont été influencées par le type de matrice et le matériau de la peau 2D. Les propriétés globales plus élevées ont été obtenues avec une matrice époxy suivie d'une matrice PVB. Les FML à base de PVB ont montré que leurs propriétés étaient comparables à celles de l'époxy. Le test de flexion a montré que les FML hybrides à base de PP échouaient prématurément en raison d'une délamination entre la peau synthétique et l'âme tissée 3D. L'époxy et le PVB ont montré une meilleure imprégnation du renfort contrairement au PP dans lequel seul un verrouillage mécanique a été observé. Les propriétés d'impact dynamique des composites hybrides et des FML ont montré que les caractéristiques de dissipation d'énergie étaient influencées par la matrice et l'hybridation du renforcementIn current study the mechanical properties of 3D woven jute reinforced and hybrid 3D woven jute reinforced FMLs were investigated. The four-layered 3D woven reinforcement was made with jute yarn using four types of interlocking patterns e.g. Orthogonal Through Thickness OTT and Orthogonal Layer to Layer OLL interlocking. The vacuum infusion technique was used for the fabrication of FMLs made with 3D woven jute reinforcement. After the optimization of 3D woven reinforcement the hybrid reinforced FMLs were developed in which OTT 3D woven fabric was sandwiched between 2D woven skin. Four different kinds of fibres were used to make 2D woven skin e.g. jute, aramid, carbon, and glass while three different kinds of matrix were employed, e.g. epoxy, PVB and PP. The compression hot press was used to develop hybrid reinforced FMLs. Aluminium used to make all FMLs was anodized before using for fabrication. The adhesive properties were investigated to check the quality of surface treatment, metal-composites bonding and effect of fibres and matrix. Both monotonic and dynamic properties were also investigated. The adhesive properties were characterized using t-peel and floating roller peel tests. The monotonic properties were analyzed using tensile and flexural tests. The low velocity impact performance was determined using drop weight low velocity impact test. The results showed that the anodized aluminium surface had high surface free energy so the better wetting of aluminium can be achieved by anodizing as compared to other type of surface preparations. The adhesive bonding analysis results showed that the delamination properties were mainly influenced by the nature of adhesive material rather than the type of structures of reinforcement. The nature of the matrix also influences the type of failure as with the epoxy the dominant failure was cohesive while with thermoplastic matrix it changed to adhesive and intra-laminar failure. The plasticity and ductility of matrix influenced the final properties more than the type of failure, in spite of cohesive failure of epoxy the thermoplastic matrix had more delamination force. The tensile and flexural properties of OTT 3D woven jute reinforced FMLs were higher than the OLL 3D woven reinforced FMLs due to the higher metal volume fraction, this was possible due to tighter construction of OTT fabric. The tensile and flexural properties of hybrid reinforced composites and FMLs were influenced by the type of matrix and material of 2D skin. The overall higher properties were achieved with an epoxy matrix followed by PVB matrix. The PVB-based FMLs showed that their properties were comparable with the epoxy. The flexural test showed that hybrid FMLs based on PP were failed prematurely due to delamination between synthetic skin and 3D woven core. Both epoxy and PVB showed better impregnation of the reinforcement unlike PP in which only mechanical interlocking was seen. The dynamic impact properties of hybrid composites and FMLs showed that the energy dissipation characteristics were influenced by matrix and hybridization of reinforcement
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Жигилій, Дмитро Олексійович, Дмитрий Алексеевич Жигилий, Dmytro Oleksiiovych Zhyhylii, Володимир Андрійович Хворост, Владимир Андреевич Хворост, and Volodymyr Andriiovych Khvorost. "Laminated composite plates." Thesis, Видавництво СумДУ, 2004. http://essuir.sumdu.edu.ua/handle/123456789/22944.
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Oluwabusi, Oludare E. "Assessing the In-plane Shear Failure of GFRP Laminates and Sandwich Structures." University of Dayton / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1544528074090494.
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Meunier, Marion. "Dynamic analysis of FRP laminated and sandwich plates." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342851.
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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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Davies, Andrew. "Crashworthiness of composite sandwich structures." Thesis, Imperial College London, 2002. http://hdl.handle.net/10044/1/8402.
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Mechraoui, Ahmed. "Sandwich composite de mousses polymères." Thesis, Université Laval, 2010. http://www.theses.ulaval.ca/2010/27452/27452.pdf.
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L’objet de ce travail est de produire et de caractériser des composites structuraux à base de polypropylène et de mousse. La première partie est consacrée au renforcement du polypropylène avec des fibres de chanvre en étudiant l’effet de la concentration de la fibre, de la taille des fibres et de la concentration en agent de couplage sur les propriétés mécaniques. Une étude morphologique par photomicrographies a permis d’expliquer les résultats mécaniques en tension et flexion. On montre que 2% d’agent couplant est suffisant pour optimiser les modules. Dans la deuxième partie, des mousses de polypropylène sont produites par compression avec différentes concentrations d'agent gonflant afin de déterminer l’effet de la réduction de densité et du profil de densité sur les propriétés en tension et flexion. Une caractérisation complète de la morphologie des mousses en termes de taille de cellules, de densité de cellules et d’épaisseur de la peau est faite. L'utilisation du profil de densité est nécessaire afin d’obtenir une bonne prédiction des propriétés mécaniques. Finalement, des structures sandwich avec différents pourcentages de peau et de densité de cœur sont produites. Une analyse morphologique du cœur est rapportée avec les propriétés mécaniques en tension et flexion. On montre qu’une très bonne prédiction peut être faite en utilisant simplement la loi des mélanges et le modèle quadratique avec le profil de densité pour l’effet de la peau et du cœur, respectivement.The aim of this work is to produce and characterize polypropylene structural composite foams. To do so, the work is divided in three parts. The first part is devoted to study the reinforcement of polypropylene with hemp fibres by changing the fibre content, fibre size and coupling agent concentration. Micrographs are used to explain the results of the mechanical properties measured under tensile and flexural stress. It is found that 2% of coupling agent gives the optimum modulus values. In the second part, polypropylene foams are produced by compression moulding with different concentrations of blowing agent to determine the effect of density reduction and density profile on the tensile and flexural properties. The morphological characteristics (cell size, cell density and skin thickness) of the foams are also examined. It is found that the use of the complete density profile is necessary to predict with high precision the mechanical results. Finally, sandwich structures are produced with different skin ratio and core densities. A complete morphological analysis is reported with mechanical properties (tensile and flexural). It is shown that the simple law of mixture and the square power-law combined with the density profile are enough to predict the effect of the skins and core, respectively.
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Ou, Jeffrey. "Quality in composite sandwich fabrication." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36489.
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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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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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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, 1998However, 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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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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Palla, Leela Prasad. "Blast Response of Composite Sandwich Panels." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1227216480.
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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 SUPERIOREste 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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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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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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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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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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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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Deka, Lakshya J. "Quasi-static and multi-site high velocity impact response of composite structures." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008p/deka.pdf.
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Thesis (Ph. D.)--University of Alabama at Birmingham, 2008.Additional advisors: Krishan K. Chawla, Derrick Dean, Jong-Eun Kim, Mark Weaver. Description based on contents viewed Feb. 9, 2009; title from PDF t.p. Includes bibliographical references.
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Kazemahvazi, Sohrab. "Impact Loading of Composite and Sandwich Structures." Doctoral thesis, KTH, Lättkonstruktioner, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25141.
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Low weight is one of the most important factors in the design process of high speed naval ships, road vehicles and aircrafts. Lower structural weight enables the possibility of down-sizing the propulsion system and thus decrease manufacturing and operating costs as well as reducing the environmental impact. Two efficient ways of reducing the structural weight of a structure is by using high performance composite materials and by using geometrically efficient structures such as the sandwich concept. In addition to good quasi-static performance different structures have dynamic impact requirements. For a road vehicle this might be crash worthiness, an aircraft has to be able to sustain bird strikes or debris impact and a naval ship needs to be protected against blast or ballistic loading. In this thesis important aspects of dynamic loading of composite and sandwich structures are addressed and presented in the appended papers as follows. In paper A the notch sensitivity of non-crimp fabric glass bre composites is investigated. The notch sensitivity is investigated for several different laminate con gurations at varying tensile loading rate. It is shown that the non-crimp fabrics have very low notch sensitivity, especially for laminate con gurations with a large amount of bres in the load direction. Further, the notch sensitivity is shown to be fairly constant with increasing loading rates (up to 100/s). In paper B a heuristic approach is made in order to create an analytical model to predict the residual strength of composite laminates with multiple randomly distributed holes. The basis for this model is a comprehensive experimental programme. It is found that unidirectional laminates with holes predominantly fail through three failure modes: global net-section failure, local net-section failure and local shear failure. Each failure mode can be described by a physical geometric constant which is used to create the analytical model. The analytical model can predict the residual strength of unidirectional laminates with multiple, randomly distributed holes with good accuracy. In paper C and paper D, novel prismatic high performance all-composite sandwich cores are proposed. In paper C an analytical model is developed that predicts the strength and sti ness properties of the suggested cores. In paper D the prismatic cores are manufactured and tested in shear loading and out-of-plane compression loading. Further, the analytical model is used to create failure mechanism maps to map out the overall behaviour of the different core con gurations. The novel cores show very high speci c strength and sti ness and are potential candidates as cores in high performance naval ship hulls. In paper E the dynamic properties of prismatic composite cores are investigated. The dynamic out-of-plane strength of an unit cell is tested experimentally in a gas gun - Kolsky bar set-up. Especially, different failure mechanisms and their e ect on the structural strength are investigated. It is found that cores with low relative density (slender core members) show very large inertial stabilisation e ects and have a dynamic strength that can be more than seven times higher than the quasi-static strength. Cores with higher relative density show less increase in dynamic strength. The main reason for the dynamic strengthening is due to the strain rate sensitivity of the parent material rather than inertial stabilisation of the core members.QC 20101014
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Denli, Huseyin. "Structural-acoustic optimization of composite sandwich structures." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 168 p, 2007. http://proquest.umi.com/pqdlink?did=1251904511&Fmt=7&clientId=79356&RQT=309&VName=PQD.
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Åkermo, Malin. "Compression moulding of thermoplastic composite sandwich components /." Stockholm, 1999. http://www.lib.kth.se/abs99/aker0422.pdf.
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SerraniÌa-Soto, Florencia. "Low velocity impact of composite sandwich panels." Thesis, Queen Mary, University of London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398305.
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Zangani, D. "Modelling of z-Core composite sandwich panels." Thesis, University of Newcastle Upon Tyne, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533691.
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Cowan, Andre James. "Sound Transmission Loss of Composite Sandwich Panels." Thesis, University of Canterbury. Mechanical Engineering, 2013. http://hdl.handle.net/10092/7879.
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This thesis examines the sound transmission loss (STL) through composite sandwich panel systems commonly used in the marine industry. Experimental, predictive and optimisation methods are used to evaluate the acoustic performance of these systems and to improve their acoustic performance with noise treatment.
The complex nature of the material properties of composite sandwich panels was found to be dependent not only on the physical properties but also the frequency of incident noise. Young’s modulus was found to reduce with increasing frequency as has been predicted in the literature which is due to the shear stiffness dominating over the bending stiffness. Two methods for measuring these properties were investigated; ‘fixed-free’ and ‘free-free’ beam boundary condition modal analyses. The disagreement between these methods was identified as the clamping fixed nature that increased flexibility of the beam.
Composite sandwich panels can be modelled as homogeneous isotopic materials when predicting their acoustic performance provided the dilatational resonance is above the frequency range of interest. Two such panels were modelled using this simple sound insulation prediction method, but the agreement between theory and experimental results was poor. A variable Young’s modulus was included in the model but agreement remained relatively poor especially in the coincidence frequency region due to variation of Young’s modulus with frequency.
A statistical method of optimisation of the parameter settings by fractional factorial design proved successful at identifying the important parameters that affect the sound transmission class (STC) of a noise treatment material applied to a panel. The decouple foam layer and attachment method were the most significant factors. The same method, with higher resolution was then used to identify the important parameters that affected the noise reduction class (NRC) finding that the outer foam thickness without a face sheet were the most significant factors. The independent optimisation studies performed for each of the STC and NRC produced conflicting results meaning that both could not be achieved simultaneously.
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Akil, Hazizan Md. "The impact response of composite sandwich structures." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399096.
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Trask, Richard Simon. "Damage tolerance of repaired composite sandwich structures." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416072.
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Maheri, M. R. "Vibration damping in composite/honeycomb sandwich beams." Thesis, University of Bristol, 1991. http://hdl.handle.net/1983/d96ba3e9-edb0-4a07-ac6e-69328ed22678.
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Lee, Chang-Yong. "Dynamic Variational Asymptotic Procedure for Laminated Composite Shells." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16265.
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Unlike published shell theories, the main two parts of this thesis are devoted to the asymptotic construction of a refined theory for composite laminated shells valid over a wide range of frequencies and wavelengths. The resulting theory is applicable to shells each layer of which is made of materials with monoclinic symmetry. It enables one to analyze shell dynamic responses within both long-wavelength, low- and high-frequency vibration regimes. It also leads to energy functionals that are both positive definiteness and sufficient simplicity for all wavelengths. This whole procedure was first performed analytically. From the insight gained from the procedure, a finite element version of the analysis was then developed; and a corresponding computer program, DVAPAS, was developed. DVAPAS can obtain the generalized 2-D constitutive law and recover accurately the 3-D results for stress and strain in composite shells. Some independent works will be needed to develop the corresponding 2-D surface analysis associated with the present theory and to continue towards full verification and validation of the present process by comparison with available published works.
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Mespoulet, Stephane. "Through-thickness test methods for laminated composite materials." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/7314.
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Li, Nong. "Vibration of laminated orthotropic composite plates and shells." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6946.
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Almost all of the analytical solution techniques presented for composite plates and shells deal with either simply supported conditions or boundary conditions with at least a pair of opposite edges simply supported. In the present study, an alternative general approach, combining superposition and state space techniques is developed for the free vibration analysis of laminated orthotropic composite plates and shells having arbitrary boundary conditions. This study concentrates on the antisymmetric angle-ply laminated plates and cross-ply laminated plates and shells. Three commonly adopted theories, i.e., classical theory, first-order shear deformation theory and third-order shear deformation theory, have been employed and compared with one another to investigate the influence of transverse shear deformation, structural aspect ratio, length-to-thickness ratio, degree of anisotropy and the number of layers on natural frequency. Convergence tests have been carried out to guarantee the accuracy of the closed-form solutions. Wherever possible, numerical results generated by the present approach are compared with those reported in the published references. Accurate non-dimensional fundamental frequencies are presented for laminated plates and shells with two adjacent edges, three edges and four edges clamped and other edges simply supported. Such analyses have not been reported in the literature previously. Also, vibration analysis of a cantilever angle-ply antisymmetric plate with a point support is conducted to demonstrate the applicability of the present technique. It has been shown that the method works extremely well and excellent agreements are found between the present results and those generated by previous researchers. It has also been shown that more complicated boundary-value problems can be solved by this technique without any difficulty.
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Thije, René Hermanus Willem ten. "Finite element simulations of laminated composite forming processes." Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/57908.
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Watkins, R. I. "Multilevel optimum design of large laminated composite structures." Thesis, Cranfield University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374011.
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Zheng, Daihua. "Low Velocity Impact Analysis of Composite Laminated Plates." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1194991384.
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