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Multi-stable composite laminates have been widely investigated for morphing applications due to distinct geometrical characteristics about each stable configuration. Recently, a mechanism for realizing on-demand stiffness adaptation in compliant structures has been proposed exploiting the stiffness variation from switching between the stable states of embedded bi-stable laminates. This allows for reducing the coupling between loading and morphing deformation modes , broadening the overall design space for morphing structures . However, the design of such embeddable laminates requires the study of multiple lamination domains to allow embedding within larger compliant structures. This process is currently done by computationally expensive simulations. We present an analytical model to predict the stable shapes and structural characteristics of multi-section, multi-stable composite laminates subject to two clamped boundary conditions. The analysis is conducted employing the Rayleigh-Ritz method using polynomial approximations of the displacement fields. The structural characteristics are predicted while constraining the laminate edges, thus extending previous models designed to account mainly for free edge boundary conditions. Our model is subsequently applied to explore the design space for characterizing the stability and variable stiffness properties of two different classes of bi-stable laminates. The presented model allows for the efficient design of multi-stable laminates embeddable within compliant structures.

In this article, performance of the elliptical patches of smart constrained layer damping (SCLD) treatment is investigated for controlling vibrations of smart laminated composite plates. A three dimensional mesh free model (MFM) has been implemented for the first time based on the element free Galerkin (EFG) method and layer wise displacement theory for studying the dynamic behavior of the composite plates integrated with the SCLD treatments. Symmetric/antisymmetric cross-ply and general angle-ply laminates are considered for the substrate of the smart composite plates. Circular and regular rectangular type patches are also considered for the analysis. It is observed that the elliptical SCLD patches are more efficient in attenuating the amplitude of vibration in the laminated composite plates as compared to the circular and square type patches. The results from numerical analysis also reveal that the elliptical patches have the maximum performance index followed by the circular and the square type SCLD patches in enhancing the active damping characteristics of smart composite plates. The performance of the elliptical patch is sensitive to the piezoelectric fiber orientation angle and becomes maximum if the piezoelectric fiber orientation is vertical irrespective of the types of SCLD patches considered as well as the lamination sequence.

Helicopter power transmission systems consist of aluminum drive shafts which are connected together with flexible couplers to accommodate misalignment and hanger bearings to secure each drive shaft to the airframe . The development of carbon fiber composites have resulted in designs which reduce the weight of the system as well as eliminate parts which can be integrated into the composite material itself. The reduction in weight and parts provide transmissions which are more maintenance cost conscious as downtime related to manual part inspection for defects and damage is reduced. One barrier to fielding composite systems is impact qualification to ensure passing of survival standards. Some certainty that a design will not increase the vulnerability of a vehicle must exist and this paper provides an impact study for flexible composite drive shafts and performs a design analysis on tradeoffs between weight, and residual strength . 16 drive shafts with two different thicknesses and the optimized lamination [±45 6/±402] were manufactured and impacted with either 7.62 or 12.7 mm projectiles while under 252 N-m of torque.

In this paper a theoretical analysis for determination of elastic and flexural modulus of natural fibre reinforced hybrid composite is proposed. The proposed analytical model is based on the classical lamination approach to predict the theoretical modulus. Experimental tensile and 3-point bending tests were carried out using standard specimens of inter and intra-ply hybrid composite materials. The elastic and flexural modulus predicted by the new approach showed a better agreement with the experimental results, with a maximum deviation of 11.21% and 11.65 % respectively. From the results it was observed that the theoretical value of elastic and flexural modulus was not accurately predicted by rule of hybrid mixture method. The proposed approach can be adopted as a primary tool to predict the modulus of the composite and it can also be used to optimise the composite parameters such as volume fraction of fibre, ply and fibre orientation, etc. for the maximum performance.

This paper investigates buckling behavior of functionally graded graphene-reinforced composite (FG-GRC) laminated plates. The extended Halpin-Tsai model is used to estimate the effected material properties of the GRCs. The effects of rotary inertia and transverse shear deformation are incorporated by the first-order shear deformation theory (FSDT). Using the meshless kp-Ritz method, the buckling solutions are obtained. In order to derive the discretized eigenvalue equation, the kernel particle approximation is employed in the field variables and the energy functional is minimized through the Ritz procedure. The stability and accuracy of the meshless kp-Ritz method is verified through comparison and convergence studies by considering the effect of support size and number of nodes. The effects of boundary temperature, distribution of graphene, plate width-to-thickness ratio, plate aspect ratio and number of layers are investigated by detail parametric studies. Besides, the influences of boundary conditions, the types of buckling load and lamination angle are considered in this paper.

This paper presents a weak form quadrature element formulation in the analysis of nonlinear bifurcation and post-buckling of cylindrical composite laminates subjected to transverse loads. A total Lagrangian updating scheme is used in combination with arc-length method and the branch switching method is adopted to identify the whole post-buckling procedure of the laminates. The formulation of the shell model is based on the basic concept of Ahmad. The coincidence of discrete nodes and integration points in quadrature element endows it with compactness and conciseness in the nonlinear buckling analysis of cylindrical laminates. Shear and membrane locking problems are avoided in the quadrature element formulation for its high-order approximation property. Several numerical examples are firstly presented to verify the effectiveness and accuracy of the present formulation. Parametric studies of the effects including rise, thickness, boundary conditions and lamination scheme of the cylindrical composite laminates on the bifurcation and post-buckling behaviors are performed.

In this paper, thermal buckling analysis of variable stiffness composite laminate (VSCL) is carried out. The first-order shear deformation theory is adopted with eight noded isoparametric element to construct a finite element model for thermal buckling analysis. The effect of the uncertain composite properties that could arise due to complex manufacturing and fabrication process to the buckling temperature is investigated using polynomial neural network (PNN). The contribution of individual properties, such as the material properties, fiber orientations, and the thermal expansion coefficients of VSCL plate are performed for various boundary conditions and lamination sequences. A sensitivity analysis is also carried out and parameters to which buckling temperature has high sensitivity are identified. The accuracy and efficiency of PNN model are compared with Monte Carlo simulation (MCS). Further, PNN is employed to evaluate the reliability parameters of VSCL plate. From the various studies, it is observed that even though the influence of different stochastic input parameters are depend on the boundary conditions, the transverse coefficient of thermal expansion ( α 22 ) is found to be most influential parameter, followed by transverse ( E 22 ) and longitudinal ( E 11 ) Young’s modulus, respectively.

The existence of cracks has a great influence on the life span of the envelope material of aerostats, especially for stratospheric airships that operate in harsh environments. Understanding the relationship between fracture mechanism and composite structure of envelope materials is of great significance to the design and development of envelope materials. To explore the fracture mechanism of envelope material, a novel polyimide (PI) envelope was developed by lamination method. Then, the fracture behavior and mechanism of PI envelope with single edge crack was studied and analyzed in detail by means of experimental method and theoretical model analysis. It was found that the crack orientation has no significant effect on the fracture strength of PI envelope, while the increase of crack length will increase the strength loss rate and decrease the crack sensitivity. These phenomena suggest that the fracture strength loss of envelope is mainly determined by the number of cut-off longitudinal yarns. And the stress transfer effect of coating and transverse yarns which causes stress concentration in the crack tip region is another important factor affecting the fracture strength of PI envelope. Besides, the interfacial properties between coating and fibers as well as the size effect of coating also play an important role in the fracture property of PI envelope. Finally, stress intensity factor theory and critical stress field theory were chosen to study the fracture behavior of PI envelope. The calculation results indicated that critical stress field theory can better predict the fracture strength of PI envelope.

In this study, energy harvesting from cantilever composite beams produced at different lamination angles was experimentally investigated. In this regard, three different eight layered laminated composite beams are considered, i.e., {0 degrees, 90 degrees, 0 degrees, 90 degrees}s, {-30 degrees, 60 degrees, -30 degrees, 60 degrees}s and {-45 degrees, 45 degrees, -45 degrees, 45 degrees}s. energy harvest performances were analyzed under different external dynamics inputs by bonding piezoelectric material to the surface of composite beams. Firstly, the composite beam harvesting structure was excited by air-flow. In those experiments, three different types of bluff-body geometry elements were attached to the free end for each of the considered composite beams. In order to determine the maximum power output, different resistors are attached to the piezoelectric material. As a second dynamic input, an electromagnetic actuator operating on the Lorentz principle is used. By using this electromagnetic actuator, the structures are excited by harmonic inputs with different frequencies and frequency-voltage responses were obtained. Besides, vibration amplitudes and voltage outputs were analyzed for both excitation types.

In this paper, free vibration behavior of carbon nanotube (CNT) reinforced functionally graded thick laminated composite plates utilizing Reddy’s higher-order shear deformation theory (HSDT) is studied. To the best of authors’ knowledge, this paper is the first to incorporate HSDT with one of the element-free approaches to investigate this issue. The element-free IMLS-Ritz method is employed and four types of CNT distributions are considered. The resulting effective material properties of the CNT-reinforced composite are estimated by a detailed and straightforward Mori–Tanaka approach. The numerical results have been compared with the literature showing excellent agreement. Considering various CNT orientation angles, a parametric study showing the effects of CNT volume fraction, plate aspect ratio, plate width-to-thickness ratio and number of plate’s layers on the non-dimensional natural frequencies is investigated. Finally, the influence of boundary conditions on the sequence of the first six mode shapes for various lamination arrangements is presented.

Natural fibers are fostered to replace traditional fibers in long-fiber composites due to their reduced environmental impact. While carbon fibers compete on a league on their own, natural fibers are foreseen to be a viable alternative to glass fibers due to a similar specific strength under certain loading conditions. The purpose of this paper is to compare the impact resistance of natural fiber composites against a similar glass-fiber counterpart. This work presents an experimental study investigating low-velocity impacts on stress-free flax- and glass-based laminates sharing the same matrix system, have similar quasi-isotropic lamination sequences, and have been designed to be similar in weight. Such an approach further leads to laminates with similar flexural modulus , allowing for a direct comparison of the impact resistance. Insights on the major damage mechanism and the damage evolution during the impact are further gained through numerical simulations. Results show that the impact resistance of natural fiber composites is drastically lower than their glass counterparts, and such behavior should be mainly ascribed to the lower fiber strength. Further, the proposed numerical model gives insight on modeling parameters that can be utilized to improve the reliability of the numerical solution in terms of energy absorption during the impact.

The work is devoted towards incorporating the Murakami zig-zag function (MZZF) for modelling the active constraining layer damping (ACLD) treatment of ‘N’ layered laminate cylindrical shells. The ACLD treatment in the patch form comprises of two material layers with the viscoelastic material layer constrained between the host shell and the smart 1–3 piezoelectric composite (PZC) material layer. The kinematics of deformation are derived successfully implementing the MZZF in the displacement fields. Virtual work principle has been employed for the finite element (FE) model to deduce governing equations of shell ACLD system in complete form. A feed-back control system has been considered to arrive at closed loop governing equations of motion. Considering the above, a MATLAB code for the same is generated to emphasise on dynamics of the cylindrical shell ACLD system. Cylindrical shells with various lamination schemes have been considered to assess the validity and implementation of MZZF for ACLD treatment of shells. Also, the oblique orientation of the 1–3 PZC material layer and its effect on the damping behavior of the cylindrical shell has been thoroughly explored.

The vibration of a magnetostrictive laminated composite sandwich plate with a viscoelastic core and faces rested on the two-parameter elastic medium is analyzed in the present article. The laminated sandwich plates are designed wherein consist of three kinds of composite materials: magnetostrictive material, fiber-reinforced material, and viscoelastic material in the core and faces. The viscoelastic core and faces are modeled as a Kelvin-Voigt viscoelastic model. The partial differential equations of motion are derived by implementing Hamilton’s principle. The analytical Navier’s solution type is obtained to analyze the behavior of the damping coefficient and the damped natural frequency coefficient. The influence of significant parameters is examined on vibration characteristics of the plate and discussed in detail, especially, location of smart layers, lamination schemes, elastic foundation coefficients, modes, the magnitude of the feedback coefficient, viscoelastic structural damping, thickness ratio, the aspect ratio, and viscoelastic layer thickness-to-magnetostrictive layer thickness ratio. Numerical results illustrate that the location of smart layers is an important element in the design of the plate to be more stable. It is anticipated that the findings reported in the study can be utilized to develop the adaptive structural applications and the solutions to future smart structure problems.

In this paper, the post-buckling behavior of laminated nanocomposite plates subjected to biaxial and uniaxial compression is investigated. In each layer, carbon nanotubes (CNTs) are axially aligned within the polymer matrix, and are distributed either uniformly or in a functionally graded pattern in the thickness direction. Discretized governing equations are derived based on the first-order shear deformation theory (FSDT) via the IMLS-Ritz method. In this study, the post-buckling paths are traced using an algorithm that combines the arc-length iterative procedure with the modified Newton–Raphson method. In order to validate the method, comparison studies are performed on the functionally graded material laminated plates, where results are available in the literature. Several example problems are considered including cross-ply and angle-ply laminated nanocomposite plates. The effects of number of layers, lamination scheme, plate geometry, CNT volume fraction ratio, CNT distribution, and boundary conditions on the post-buckling behavior of the plates are presented.

Buckling behavior of carbon nanotube reinforced functionally graded (CNTR-FG) composite laminated plate is studied. The first-order shear deformation theory (FSDT) is employed to incorporate the effects of rotary inertia and transverse shear deformation, and the meshless kp-Ritz method is used to obtain the buckling solutions. Using the kernel particle approximation in the field variables and minimizing the energy functional via the Ritz procedure, a discretized eigenvalue equation of the problem is derived. The numerical stability and accuracy of the kp-Ritz method is validated through convergence and comparison studies. Besides, parametric studies are conducted for various types of CNTs distributions, CNT volume fraction, plate aspect ratio and plate length-to-thickness ratio under different boundary conditions. Moreover, the effects of number of layers and lamination angle are also investigated.

High pressure vessels with winding lamination of [90°/±15°] were manufactured adopting a vinylester and an epoxy resin reinforced with carbon fibres. An experimental setup was design to test the vessels up to the burst pressure. The tests results demonstrate a higher ultimate pressure of the carbon/vinylester composite vessel with respect to the epoxy reinforced counterpart. The full field strain measurements by the digital image correlation technique show a delayed of the initiation and propagation of the damage in the carbon/vinylester. Moreover, the carbon/vinylester vessel performed more homogeneous strain distribution with less and shorter hoop cracks than the carbon/epoxy one, as observed also with an X-ray micro tomography system, a laser microscope and a scanning electron microscope.

The present work aims to derive the mechanical properties of a unidirectional (UD) lamina from experimentally measured properties of non-flat (cylindrical) laminated specimens. The specimens were cut from carbon fiber-epoxy tubes having cross-ply and angle-ply layup configurations. Special tests were designed and applied on these specimens to measure the mechanical properties of the laminate, Ex, Ey, νxy, Gxy, as well as tensile and shear failure strength. By using the classical laminate theory (CLT), the mechanical properties of UD lamina, E1, E2, ν12 and G12 were expressed explicitly as functions of the measured properties of the cross-ply laminate and in form of effective mechanical properties of general lamination configuration like the angle-ply layup. A new shear test fixture was designed in order to obtain the in-plane shear modulus and shear strength of ring-shaped composite specimens. This shear test fixture has proved to be advantageous, especially when one bears in mind that there are very few shear test methods for cylindrical components. The outcomes of this work would be useful for material characterization and quality control when standard flat coupons are not available.

This article highlights the design and development of lightweight composite pins using carbon prepreg through the filament winding molding and heat-shrinkage fitting processes for heavy load long pitch roller chains. A structural analysis is performed to confirm the stress distribution of this composite pin based on the lamination structure. The stresses on the plates and pins of the roller chain are analyzed. The structural analysis was performed at maximum load, and the results endorsed the design of a pin with an inner diameter of 20 mm and an outer diameter of 34 mm to be optimum. According to the analysis results, prototypes are fabricated, and fiber volume fraction and porosity of the composite pin were evaluated. The composite pin was inserted into the steel hollow tube using heat shrinkage fitting process, and the damping ratios and weights of these pins were measured. The composites with a fiber volume of 60% and a porosity of 0.52% demonstrated a significant increase in damping ratio (27%) and an 18.6% reduction in weight compared to the steel pin. Overall, inserting the composite pin into steel chain is established as a novel approach to improve the structural design of the heavy load long pitch roller chain for attaining effective durability.

Laminated glass components are usually realized by bonding glass plates using interlayer polymers that develop adhesion forces during lamination. Recently, these adhesion forces have been used also to realize special adhesive connections for structural glass components and assemblies. The typical example of such a joining technique is conventionally known as “embedded laminated connection”, where a metal insert is encapsulated in multi-ply laminated glass components. In this study, careful consideration is paid for the investigation of the mechanical behaviour of embedded laminated connections with thick metal insert. To this aim, small-scale laboratory tests, Finite Element (FE) numerical models and analytical considerations are presented. Firstly, the results of experimental investigations at different temperatures are discussed, giving evidence of the geometrical and mechanical parameter effects on the so observed performances. It is observed, in particular, that the temperature markedly affects not only the maximum load carrying capacity but also the failure mode of the studied connection typology. Non-linear numerical simulations are then developed in ABAQUS on refined FE models, able to account for the geometrical and mechanical properties of the reference connection specimens. Further analytical considerations are also presented, in support of the observed experimental findings. It is shown, in particular, that as far as high temperatures are not attained, the mechanical performance and failure mode of the examined connections is strictly related to glass breakage. In addition it is also observed that at high temperature, failure mode (i.e. bubble formation) and failure location are in line with the expectations. Rather close correlation can be also found for the same embedded connections between test results, FE numerical simulations and analytical assumptions.

The present study deals with numerical and experimental investigations on free vibration behavior of woven fiber Glass/Epoxy laminated composite shells subjected to hygrothermal environments. A composite doubly curved shell model based on first order shear deformation theory (FSDT) is considered for free vibration of shells subjected to elevated temperatures and moisture concentrations. A quadratic eight-noded isoparametric element is used for the analysis. Series of experiments is conducted to obtain natural frequencies of vibration for woven fiber Glass/Epoxy laminated composite shells using B&K FFT analyzer with PULSE software. Parametric study is carried out varying the curvature ratios, number of layers of laminate and lamination sequences on fundamental natural frequencies of laminated composite shells for different temperature and moisture concentration under different boundary conditions. The numerical and experimental results show that there is a reduction in natural frequency of laminated composite shells with the increase in temperature and moisture concentrations.

This paper presents the first-known vibration analysis of thin-to-moderately thick laminated functionally graded carbon nanotube (FG-CNT) reinforced composite rectangular plates. The laminated plate is composed of perfectly bonded CNT-reinforced functionally graded layers. Different distributions of single walled carbon nanotubes (SWCNTs) through the thickness of layers are considered; uniform and three kinds of functionally graded distributions of carbon nanotubes along the thickness direction of plates. Using the extended rule of mixture, material properties of the laminated nanocomposite plates are estimated. The present formulation is based on the first-order shear deformation theory (FSDT) and the analysis is carried out using the kp-Ritz method. In this study, the effects of the volume fractions of CNTs, plate width-to-thickness ratio, plate aspect ratio, distribution type of CNTs and boundary conditions on the natural frequencies and mode shapes of the laminated FG-CNT reinforced composite plates. Besides, the effects of number of layers and lamination angle are also examined.

The present work deals with the design of a graded fiber-reinforced composite lamina and graded laminates with an objective of reduced inter-laminar stress-discontinuity in composite laminates. First, the micro-structure of composite lamina is designed and its graded elastic properties are predicted. Next, its utility is demonstrated through the proposition of a new lamination scheme in which a conventional laminated composite plate (CLCP) is converted to a graded laminated composite plate (GLCP). The usefulness of the present design in attaining continuous stresses at the inter-laminar surface of composite laminates is verified through a static analysis. For conversion of a CLCP into a GLCP, the changes in the dynamic characteristics are also presented by analyzing the nonlinear frequency responses of CLCP/GLCP integrated with a layer of active constrained layer damping (ACLD). The dynamic analysis clarifies the suitability of proposed lamination scheme for the use of GLCP under transverse harmonic loads.

The small mass impact, such as runway debris and dropped tools, is a major issue during the design of composite plates, as it may significantly reduce the plate strength and stiffness without any visible damage. This work presents a novel optimization procedure to maximize the critical buckling load of composite plates subjected to small mass impact considering impact response and delamination threshold load predicted by closed forms solutions. The optimization is based on lamination parameters combined with laminate databases. In the first phase of the optimization a simplified model is used to obtain an approximate optimum. A design optimization using refined finite element model starting from the previous phase optimum is performed. The proposed algorithm is efficient, robust and applicable to many optimization problem for composite plates.

An analytical model to predict the fatigue life of a composite laminate is formulated. The model calculates stresses in each ply using classical lamination theory, degrades the residual strength using the linear wear-out law and predicts failure based on Tsai Wu failure theory. The cycles to failure are predicted using the updated cycle-by-cycle probability of failure. The predictions are validated for both a constant amplitude and a variable amplitude loading on a Glass/Epoxy laminate. Additionally the analytical model is extended to work with laminates described using lamination parameters instead of ply angles and stacking sequence. The analytical fatigue model is then integrated in the TU Delft aeroelastic and structural optimization tool PROTEUS. A thickness and stiffness optimization of the NASA Common Research Model (CRM) wing has been carried out. Results show that fatigue, strength and stiffness are the design drivers in the aeroelastic optimization of a composite wing. Furthermore, by including the analytical fatigue model instead of using a traditional knockdown factor to account for fatigue, a lighter wing is obtained.

This research paper presents the dynamic and aeroelastic analysis of functionally graded carbon nanotube reinforced (FG-CNTRC) laminated composite plates with damage in the subsonic regime. First order shear deformation theory (FSDT) is applied to develop finite element code in MATLAB environment for structural analysis. The anisotropic damage formulation based on the concept of stiffness reduction is introduced into the finite element formulation to include the damage in the plate. To implement aeroelastic analysis through PK-method, the required aerodynamic force matrix coefficients, are generated in MSC.Nastran by supplying modal parameters (obtained from structural analysis) through direct matrix abstract program (DMAP) using doublet-lattice-method (DLM). The accuracy of the present model has been analyzed by tackling the various numerical illustrations and validated with some of earlier published literature. Further, the effect of various parameters like CNT fiber volume fraction, lamination sequence, damage location and orientation on flutter characteristic are studied.

Static response characteristics and failure load of laminated composite shallow cylindrical and conical panels subjected to internal/external lateral pressure are investigated using continuum damage mechanics approach considering geometric nonlinearity and damage evolution. The damage model is based on a generalized macroscopic continuum theory within the framework of irreversible thermodynamics and enables to predict the progressive damage and failure load. Damage variables are introduced for the phenomenological treatment of the state of defects and its implications on the degradation of the stiffness properties. The analysis is carried out using finite element method based on the first order shear deformation theory. The nonlinear governing equations are solved using Newton–Raphson iterative technique coupled with the adaptive displacement control method to efficiently trace the equilibrium path. The detailed parametric study is carried out to investigate the influences of geometric nonlinearity, evolving damage, span-to-thickness ratio, lamination scheme and semi-cone angle on the static response and failure load of laminated cylindrical/conical panels. It is revealed that the membrane forces due to geometric nonlinearity significantly influence the damage distribution and failure load.

Designing a laminate based on its stiffness properties requires finding the optimum lamination stacking sequence to yield the required stiffness properties. The design variables to be considered are the number of layers and orientation angle of fibers in each layer group, which are treated as discrete-variables. The optimum lamination is then obtained by minimizing a cost function composed of the relative difference between the calculated effective stiffness properties and weight of trial laminate and the desired properties. This error minimization problem was solved using a modified simulated annealing heuristic method. The new simulated annealing implementation comprises a cooling procedure in which the temperature decrease relied adaptively on the objective function evolution. It is shown that the proposed method can give rise to an improvement in convergence speed. To achieve a further improvement in the performance of the method, simulated annealing parallelization implemented using the proposed cooling process. The main features of this algorithm are described and its encouraging results are presented.

In this paper, the buckling analysis of symmetrically laminated composite plates with internal supports was proposed. Both the higher-order shear deformation theory and pb-2 Ritz displacement functions, corresponding to an arbitrary edge support were enclosed in the proposed method. The buckling behavior of symmetrically laminated composite plates with line internal support and, circular internal supports were investigated under biaxial compression loading. Numerical results highlighted the effect of lamination angles, edge conditions, aspect ratio, and internal supports on critical buckling load. It was confirmed that the present method was an effective one and could be widely used to analyze the buckling load and to predict the buckling characteristics of laminated composite plates with internal supports.

A new formulation for the critical thrust force necessary to propagate the delamination generated during the drilling operation of an antisymmetric angle-ply laminate is proposed by modeling the delamination zone as an elliptical shape. The critical thrust force is analytically derived with the consideration of bending, twisting and mid-plane extension of the delamination zone. And then to maximize the critical thrust force, the optimal design of an angle-ply laminate is performed to find the optimal number of fiber per millimeter, optimum diameter of fiber and optimum lamination angle using ADS (Automated Design Synthesis).

This paper deals with the study of tensile buckling, vibration and dynamic stability behaviour of multilaminated curved panels subjected to uniaxial in-plane point and patch tensile edge loadings by using the finite element method. The effect of first order shear deformation theory is used to model the doubly curved panels. Numerical results have been established through convergence and comparison with the published data from the literature. The effects of load position, number of layers, lamination angles, thickness ratio, aspect ratio and shell geometries of the panel are considered in the analysis and results are discussed.

Strengths of laminated composite pressure vessels are studied via both analytical and experimental approaches. Experimental techniques are presented to determine the first-ply failure and burst strengths of laminated composite pressure vessels with different lamination arrangements. Different analytical methods, together with various failure criteria, are used to predict the first-ply failure strengths of the laminated pressure vessels. The accuracy of the theoretical prediction of first-ply failure strength is verified by the test data. The suitability of the failure criteria, as well as the limitations of the analytical methods are discussed.

Thermal response of antisymmetrically laminated metal matrix composite (MMC) plates subjected to non-uniform temperature field is analysed. Temperature dependence of both elastic and viscoplastic properties of the metallic matrix is taken into account; this suggests that a non-uniformly heated plate should be considered as a non-homogeneous structure. A micro-to-macro approach is employed to establish the instantaneous thermo-inelastic constitutive law at each point of the plate and to perform the structural analysis. Results are presented for simply-supported and clamped graphitealuminium plates. The effects of boundary conditions, lamination angle, length-to-thickness ratio and different types of spatial temperature distributions are illustrated. Comparisons with the results obtained using an approach that treats the effect of temperature-dependent material properties in a simplified manner are shown. Comparisons with the corresponding elastic solutions (which neglect the inelastic effects in the metallic matrix) are given.

This paper presents finite element results and some experimental data on the free vibration of symmetric laminated composite plates containing a central hole. The varying parameters in the study are the hole sizes, the boundary conditions along the edges of the plate and the aspect ratio of the plate. Hole diameters ranging from 0.1 to 0.9 times the width of the plate and the aspect ratio varying from 1 to 4 were analysed in the numerical study. The other parameters such as the stacking sequence and the lamination materials are kept constant. The stacking sequence and material properties chosen for the study are those typically found in aircraft structural applications. The close correlation between numerical and experimental data provides some confidence in the finite element method used.

An inelastic bifurcation buckling of symmetrically laminated metal matrix composite (MMC) plates under non-uniform thermal loading is analyzed. The metallic matrix is modeled as a thermoelasto-viscoplastic material with temperature-dependent properties (both elastic and viscoplastic). This suggests that, in the prebuckling state, a MMC plate should be considered as a statistically non-homogeneous thermoelasto-viscoplastic structure. To treat the problem, a method based on a combination of micromechanical and structural analyses is used. As a result, a buckling criterion, incorporating the effective instantaneous constitutive behaviour at every point of the plate at each increment of thermal loading, is obtained. Results are presented for simply supported and clamped SiC/Ti plates. The effects of length-to-thickness and aspect ratios, lamination angle, fiber volume fraction, and different types of spatial temperature distributions on the critical buckling temperature are illustrated. Comparisons with the results obtained using an approach that treats the effect, of temperature-dependent material properties in a simplified manner, are presented. Comparisons with the corresponding elastic solutions, obtained by neglecting the inelastic effects in the metallic matrix, are given.

A circular thin-walled cylinder subject to bending is studied. The optimal radius, wall thickness, and lay-up is obtained under a buckling constraint similar to that of the NASA Space Vehicle Design Criteria, and a global bending stiffness constraint. The lay-up is restricted to symmetric laminates but otherwise with complete freedom in the lay-up angle variation through the thickness, which is obtained by using lamination parameters as design variables. By neglecting the influence of geometry and stiffnesses on the knock-down factor for buckling, the optimal lay-up is found to be independent of the requirements of buckling strength and stiffness, i.e. all cylinders of a specific material will have the same optimal lay-up.

An analytical study is presented in this paper on the effect of material nonlinearity on buckling and postbuckling of fiber composite laminate plates and shells subjected to general mechanical loading. The material nonlinearity of the composite is modelled by power-law type, nonlinear shear constitutive equations for each lamina. The nonlinear effective composite constitutive equations in an incremental form are incorporated into a geometrically nonlinear analysis for studying buckling and postbuckling deformations of composite laminate structures. A modified Riks' solution scheme with an updated Lagrangian formulation is used to construct the equilibrium path during composite postbuckling. Numerical examples are given to illustrate the effect of material nonlinearity on buckling load, postbuckling stiffness, and associated mode shape change of a composite structure under axial and pressure loading. Influences of lamination parameters, geometric imperfection, and loading mode on the postbuckling equilibrium path and load-bearing strength of the composite structure with the nonlinear material properties are also studied.

The optimal lamination arrangement of thick laminated composite plates for maximum damping is studied via a multi-start global optimization technique. In the optimization process, the damping analysis of a laminated composite plate is accomplished by utilizing a shear-deformable laminated composite finite element, in which the exact expressions for determining shear correction factors are adopted, with the damping model of Adams and associates. The optimal layup of the plate with maximum damping is then designed by maximizing the specific damping capacity of the plate via the multi-start global optimization technique. The effects of length-to-thickness ratio, aspect ratio, Young's modulus ratio, and number of ply groups upon the optimum ply group orientations and the value of damping are investigated by means of a number of examples of the design of symmetrically laminated composite plates.

A study is made of the thermomechanical buckling and postbuckling responses of flat unstiffened composite panels. The panels are subjected to combined temperature change and applied edge displacement. The analysis is based on a first-order shear deformation, von-Karman type nonlinear plate theory. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the plate. An efficient multiple-parameter reduction method is used in conjunction with mixed finite element models, for determining the stability boundary and postbuckling response. The reduction method is also used for evaluating the sensitivity coefficients which measure the sensitivity of the buckling and postbuckling responses to variations in the different lamination and material parameters of the panel. Numerical results are presented showing the effects of variations in the laminate stacking sequence, fiber orientation, number of layers and aspect ratio of the panels on the thermomechanical buckling and postbuckling responses and their sensitivity.

The ‘reduced bending stiffness’ (RBS) method has been used on occasions in the past as a means of simplifying the analysis of the flexural behavior of unsymmetrically laminated composite plates. However, the validity of the method has never been established. This paper makes direct comparisons between relatively simple, exact solutions for the static deflections, buckling loads and vibration frequencies of simply-supported plates and those arising from the RBS method. Extensive calculations are made for wide ranges of the physical parameters involved (aspect ratio, moduli ratio, lamination orientation angle, numbers of plies). The RBS method is found to yield sufficient accuracy for cross-ply plates, but errors up to 29% are obtained for angle-ply plates constructed with materials currently under development.

The thermal postbuckling behavior of composite laminated plates subjected to a nonuniform temperature field is investigated by the finite element method. Based on the principle of minimum potential energy, the nonlinear stiffness matrix and geometry matrix are derived. The assumed displacement state over the middle surface of the plate element is expressed as a product of one-dimensional, first-order Hermitian polynomials. An iterative method is employed to determine the thermal postbuckling load. The results of the computations reveal that the thermal postbuckling behavior of composite laminated plates is influenced by lamination angle, plate aspect ratio, modulus ratio and the number of layers.