Thick Composite Plates Research Articles

Thermomechanical postbuckling of higher order shear deformable CNT-reinforced composite plates with elastically restrained unloaded edges

Buckling and postbuckling behavior of carbon nanotube (CNT) reinforced thick composite plates resting on elastic foundations and subjected to thermomechanical loads are investigated in this paper. The plates are subjected to uniform uniaxial compression in a thermal environment or the combined action of nondestabilizing preexisting uniaxial compression and uniform temperature rise. CNTs are reinforced into matrix through functionally graded distributions. The properties of constitutive materials are assumed to be temperature dependent and effective properties of CNT-reinforced composite are determined according to an extended rule of mixture. Governing equations are based on a higher order shear deformation theory taking von Kárman nonlinearity, initial geometrical imperfection, elasticity of tangential restraints of unloaded edges and plate-foundation interaction into consideration. Analytical solutions are assumed to satisfy simply supported boundary conditions and Galerkin method is applied to obtain nonlinear load-deflection relations. Numerical analyses are carried out to show the effects of CNT distribution patterns, preexisting loads, initial imperfection, degree of in-plane constraint, and elastic foundations on the nonlinear thermomechanical stability of CNT-reinforced composite plates.

Development of a hybrid element to model intralaminar damage in thick composite plates under impact loading

This article deals with the development of a new intralaminar interface in order to extend the semi-continuous strategy already developed by the authors for impacts on thin composite laminates to thicker ones. Based on medium experimental observations scale, the new interface introduced aims at capturing transverse resin cracks occurring between fibre bundles of a unidirectional ply. The new element is implemented in the commercial finite element software Radioss®. Results of impact simulations performed on thick HTA7-913 plates (various thicknesses) are compared with experimental ones, and show good agreements in terms of both damage sizes and load-displacement curves.

Study on optimization of nozzle for copper-aluminium clad plate twin-roll cast-rolling

Use Design Modeler and Meshing module of ANSYS Workbench to complete the geometric modeling and meshing of the horizontal twin-roll mill. Combined with the Fluent fluid simulation module, a two-dimensional twin-roll cast-rolling model of a copper-aluminum composite plate and a three-dimensional model of the nozzle structure were established. Through numerical simulation of the cavity structure and end thickness of the casting nozzle, analyzed the influence of the casting nozzle structure on the flow state and outlet velocity distribution of the molten aluminum and the influence of the end thickness of the casting nozzle on the temperature field, liquid phase rate field and flow field distribution in the cast-rolling zone. The results showed that when the narrow inlet type casting nozzle had a spacing of 30 mm between the intermediate dividing block and the adjacent dividing block, the flow distribution of the nozzle cavity was reasonable and the exit velocity was relatively stable. When the thickness of the end of the casting nozzle was 4 mm, the temperature field, liquid phase rate field and flow field distribution of the aluminum liquid were reasonable, which was beneficial to the diffusion and metallurgical combination of copper and aluminum atoms. In order to verify the reliability of numerical simulation method and result analysis, the casting-rolling test was carried out with simulated process parameters. A 10 mm thick copper-aluminum composite plate was obtained by cast-rolling test. The surface was smooth and without wrinkles, and the peel strength was about 85 N/mm. The interface layer consisted of CuAl2 and Cu9Al4 and the peeling surface was torn along the intermetallic compound layer and Al matrix. The optimized nozzle structure had a great shunting effect, which verified the accuracy of the optimized model and the feasibility of the simulation to guide the production, laying a solid foundation for the preparation of high-performance copper-aluminum composite panels.

Numerical analysis of stick–slip induced nonlinear vibration and acoustic responses of composite laminated plates with friction boundaries

This paper is concerned with the development of a numerical model for predicting the nonlinear structural and acoustic responses of a composite laminated plate induced by stick–slip motions. The structural model of the plate is formulated using a higher-order shear deformation zigzag theory for accommodating the analysis of both thin and relatively thick composite plates. A phenomenological macro-slip friction model is adopted to describe the stick and slip motions of the friction boundaries. The nonlinear dynamics model of the composite plate is established based on a finite element method, and the exterior acoustic fluid is modeled using a time-domain boundary element method. The nonlinear vibro-acoustic responses of the plate are calculated by considering the compatibility conditions on the common interface of the plate and the fluid. The role of the frictional forces in the vibration and sound radiation of the plate is explained. It is found that the periodical distortions of the sound pressure waves are mainly due to the stick-to-slip transitions of the friction boundary other than the slip-to-stick transitions. The effects of the preload, friction coefficient and stiffness of the boundary on the nonlinear structural and acoustic responses of composite plates are examined.

Towards the generation of controlled one-inch impact damage in thick CFRP composites for SHM and NDE validation

In this paper, an attempt has been made to conduct controlled low velocity impact experiments in quasi-isotropic carbon fiber reinforced polymer (CFRP) composites of increasing thicknesses to generate barely visible impact damage (BVID) that creates 1″ impact damage diameter. Such impacted CFRP coupons with controlled damage diameter would serve in the future for validation of structural health monitoring (SHM) and nondestructive evaluation (NDE) damage detection methodologies. Various 2-mm, 4-mm and 6-mm thick quasi-isotropic CFRP composite plates having similar stacking sequence were manufactured in a compression molding machine. These plates were cut into numerous 6″ × 4″ coupons to be impacted in accordance with ASTM D7136 standard on a Dynatup impact testing machine. The goal of the experiments was to identify the combination of impactor mass, energy and momentum at which approximately 1″ impact damage diameter could be produced for test coupons of increasing thicknesses. Interesting observations were made with respect to the size and shape of the impact damage as the thickness of the composite coupons was increased from 2-mm to 6-mm. Modified experiments were also conducted on 6-mm coupons to achieve close to 1″ impact damage diameter. The greatest challenge in conducting these experiments was in the thick 4-mm and 6-mm coupons which did not display a predictable trend. Future work should focus on overcoming this challenge towards achieving a predictable impact damage size methodology.

BUCKLING ANALYSIS OF LAMINATED COMPOSITE PLATES UNDER THE EFFECT OF UNIAXIAL AND BIAXIAL LOADS

This paper investigates the buckling analysis of simply supported symmetrically thin and thick composite plates. Using the Hamilton’s principle, the governing equation for thin and thick composite plates is derived. The equation of motion for thin and thick laminated rectangular plates subjected to in-plane loads is obtained with the help of Hamilton’s principle. The loading conditions of rectangular plate are uniaxial and biaxial compression. Considering the Navier solution technique, closed form solutions are attained and buckling loads are found by solving the eigenvalue problems. In this study, the effect of edge ratios and anisotropy on the buckling analysis of rectangular plate was investigated. The computer programs have been written separately with the help of Mathematica (MATHEMATICA 2017) program for the solution of the buckling analysis of laminated composite plates. Results of the numerical studies for the buckling of laminated composite plates (LCP) are demonstrated and benchmarked with former studies in the literature and ANSYS finite element methods.

Effect of post-weld heat treatment on double-sided friction stir welded joint of 120 mm ultra-thick SiCp/Al composite plates

Friction stir welding (FSW) is a very promising and efficient technique in joining aluminum matrix composites (AMCs) without clear drawbacks, and post-weld heat treatment (PWHT) is a viable option to improve the mechanical properties of friction stir welded joint for heat treatable AMCs. In this work, 120 mm ultra-thick plates of 16 vol% SiCp/2014Al composites were successfully joined by double-sided FSW and subsequently friction stir welded joints were subjected to four different PWHTs (T6–25, T6–70, T4–25 and T4–70, denoting T6 or T4 heat treatment and being quenched in water at 25 °C or 70 °C after solution during heat treatment), respectively. The effect of PWHT on the distributions of microstructures and mechanical properties along the thickness direction in the nugget zone (NZ) of friction stir welded joint is investigated. For as-FSW joint, the tensile strength first decreases gradually along the thickness direction in the shoulder-affected and pin-affected regions, and then increases in the overlapping region. For T6–25 joint, the tensile strength does not vary a great deal in the shoulder-affected and pin-affected regions, and then increases slightly in the overlapping region. After T6–25 PWHT, the finer precipitates θ' are detected, aluminum grains grow up, and the tensile strength is obviously improved both in the NZ and base material attributing to the precipitation strengthening effect from finer precipitates θ'. The distributions of microstructures and mechanical properties along the thickness direction in the NZ are changed from heterogeneous distribution for as-FSW joint to nearly homogeneous distribution for T6–25 joint except in the overlapping region. After different PWHTs, the T6–25 joint shows the highest Vickers hardness in the NZ, followed by T6–70, T4–25 and T4–70 joints, and the as-FSW joint shows the lowest Vickers hardness. A comprehensive understanding can be provided for the effect of PWHT on the double-sided friction stir welded joint of thick or ultra-thick metal matrix composite plates.

On inefficiency of the shape memory alloys in dynamically loaded sandwich plates with structural damping: New 3D zigzag-viscoelasticity theory and asymmetric transformations

Abstract The important claim that the presence of the structural damping considerably lessens or even eliminates the effectiveness of the embedded shape memory elements in the dissipation of the vibration/impact energies of the structures, is stated and proven here for the first time. The finite-element-based governing equations of thick composite sandwich plates with homogeneous/FG soft viscoelastic cores and embedded SMA wires are derived based on a new hyperbolic SMA-zigzag sandwich plate theory that considers the transverse flexibility. The tension-compression asymmetry of the SMA behavior and Zener-viscoelasticity-based zigzag nonlinear corrections are implemented to guarantee the transverse stress continuity at the interfaces between layers and updating the relation between the describing parameters of the displacement field, and the stiffness and even mass matrices of the elements within each time step. For the first time, the phase-based rather than the mixture-based stresses are considered in tracing the phase transformations. The resulting time-dependent nonlinear integro-differential equations are solved by a special algorithm. Results confirm, for the first time, that the stress-strain hysteresis loops of the SMAs may shrink or even disappear in presence of the structural damping; so that, the belief that the phase-transformation-based damping and the structural damping directly add to each other, is quite wrong.

Free vibration analysis of moderately thick composite materials arbitrary triangular plates under multi-points support boundary conditions

ABSTRACT In this research, free vibration characteristics of moderately thick composite materials arbitrary triangular plates under multi-points support boundary conditions are analyzed by an improved Fourier series method. After constructing the model, the triangular region is mapped to the unit square region. The boundary conditions are simulated by five types of artificial virtual springs. In the study, in order to remove the jump or disconnect phenomenon on the boundary, all allowable displacement functions are expressed by the improved Fourier series. Combined with the chain derivative rule, energy equations are established based on the first-order shear deformation theory. Finally, the Rayleigh-Ritz technique is adopted to solve unknown coefficients. The most innovative point of the paper is to pay attention to the special multi-points support boundary conditions and combine it with the coordinate transformation of any shape triangle. The purpose of this study is to simulate actual engineering structures more accurately by studying the free vibration of triangular structure under multi-points support. It is proved that the method has higher accuracy by comparing with the finite elemet method. This method can conveniently receive the free vibration characteristics of moderately thick composite materials arbitrary triangular plates under the multi-points support boundary conditions. In addition, according to the parametric study, geometrical parameters, material properties and external boundary conditions of the structure can all affect its free vibration characteristics, which can be used as a reference for the research in this field.

Effect of overlapping region on double-sided friction stir welded joint of 120 mm ultra-thick SiCp/Al composite plates

Effective joining techniques are urgent and necessary for the rapid developments and widespread applications of aluminum matrix composite (AMC) components. Friction stir welding (FSW) is a very promising method for joining AMCs without clear defects, while double-sided FSW is especially preferred in joining thick or ultra-thick AMC plates. The overlapping region stirred twice by the two welding passes is formed during the double-sided FSW, which has an important effect on the microstructures and mechanical properties of the composite joint. In this work, 120 mm ultra-thick plates of 16 vol % SiCp/2014Al composites were successfully joined by the double-sided FSW, and an overlapping region appearing at the middle thickness of the composite joint is mainly concerned and studied. Compared with the base material and the region stirred once in the SiCp/Al composite joint, the decrease of SiC particle size, improved uniformity of particle distribution and refinement of aluminum grains and precipitates are observed in the overlapping region as a result of repetitive mechanical stirring during the double-sided FSW. The overlapping region exhibits the largest Vickers hardness and overall tensile properties: yield strength of 224 MPa, ultimate tensile strength of 369 MPa and failure elongation of 6.6%. The simultaneous enhancement in tensile strength and ductility in the overlapping region is attributed to the more effective load-transfer of reinforced particles with decreasing particle size, and the increased grain boundary strengthening due to matrix grain refinement. A comprehensive understanding the effect of overlapping region on the microstructural characterization and mechanical properties of the composite joint is positive and important to promote and accelerate the industrial applications of double-sided FSW technology in joining thick or ultra-thick metal matrix composite plates.

Prebuckling and buckling analysis of moderately thick variable angle tow composite plates considering the extension-shear coupling

In this paper, an analytical model based on a generalized Rayleigh-Ritz method is developed to deal with both the prebuckling and buckling problems of moderately thick VAT composite plates under a more general in-plane boundary condition. The non-uniform in-plane stress fields of VAT composite plates under various in-plane boundary conditions is firstly determined based on the minimum complementary energy principle combined with the Airy’s stress function. Afterwards, the governing equation of buckling problem of VAT composite plates under non-uniform in-plane stress fields is derived based on third-order shear deformation theory of Reddy’s type. The innovation of this paper lies in that a linear fitting method combined with Chebyshev-Gauss-Labotto point distribution is introduced to retrieve the boundary stress coefficients from the stress constraint conditions generated by the Lagrangian multiplier method, and meanwhile an integral expression of work done by the unknown boundary force along the prescribed in-plane displacement is adopted to satisfy the displacement constraint condition along the boundary line. In so doing, three kinds of in-plane boundary conditions are taken into account, that is, pure stress boundary condition, pure displacement boundary condition and mixed stress and displacement boundary condition. In addition, no assumption is made on the extension-shear coupling terms and thus the proposed analytical model is suitable to the unbalanced layup. The accuracy and robustness of the proposed analytical model is validated by finite element analysis and with prior results. Effects of the in-plane boundary condition, extension-shear coupling and varying fibre orientation angles on both in-plane stress and buckling responses of VAT composite plates are studied by numerical examples. It is shown that for the balanced panels under uniform compression, the benign load redistribution mechanism offered by the VAT layups remain in effect even if there exists the non-uniform shear constraint along the loading edges. However, the buckling load of the panel can be reduced by the shear constraint along the loading edges to a certain degree. Furthermore, it is found that for some displacement-controlled shear loading cases, the extension-shear coupling plays a positive role in the load redistribution, which results in a sight improvement in the longitudinal load of the panel when critical buckling occurs.

Pure S0 and SH0 detections of various damage types in aerospace composites

This paper proposes a new single-mode guided wave-based method to detect various types of damage in aerospace composites. In this method, single-mode guided wave excitation was achieved using adjustable angle beam transducers (ABT). The ABT tuning angles of various pure-mode guided waves were calculated based on Snell's law applied to the composite dispersion curves. A finite element (FE) simulation of pure S0 mode excitation in a crossply composite plate was conducted and the simulation results were validated by the experiment. For the first time, angle beam transducers were applied to generate pure shear horizontal (SH0) wave in a thick quasi-isotropic composite plate. The pure SH0 wave excitation was successfully verified by a three-dimensional (3D) FE simulation. SH0-mode wave propagation and interaction with delaminations were further conducted and strong trapped waves within the delamination regions were observed. Experiments using S0 or SH0 pure-mode guided waves were conducted to detect various types of composite damage, such as wrinkle damage in the crossply composite plate, multilayer delaminations by Teflon inserts, and actual impact damage in the thick quasi-isotropic composite plate. A significant amplitude drop was observed due to the presence of different composite damage types. In addition, a linear scanning method using pure SH0 wave was also developed to estimate the sizes of delaminations and impact damage. Both numerical and experimental results demonstrated the validity and usefulness of the proposed method for the detection of various damage types in composites.

On the stability of isotropic and composite thick plates

On the stability of isotropic and composite thick plates

Buckling Delamination of a Rectangular Orthotropic Thick Plate with an Embedded Rectangular Crack Subjected to an Axial Compressive Force

A 3D buckling delamination problem for a simply supported rectangular orthotropic composite thick plate containing a rectangular crack and subjected to an axial compressive force is studied. In the initial state, crack faces have an infinitesimal imperfection. The development of this imperfection caused by an external compressive loading along the crack is investigated within the framework of the 3D geometrically nonlinear elasticity theory of anisotropic bodies. The corresponding boundary-value problems are solved numerically by the 3D FEM. The influence of material and geometrical parameters of the plate on its critical buckling force is evaluated and discussed.

Moisture absorption in thick composite plates: modelling and experiments

Purpose When a thick structure is, on the contrary, subjected to moisture absorption, a fairly long time may be needed to reach full saturation. It is, therefore, important to understand and predict the areas of complex composite structures that are more prone to saturation. The material knock-down factors (proportional to the moisture content) may be applied only to these zones, in order to obtain a less pessimistic structural response prediction. The purpose of this paper is to investigate an FE diffusion model that was used to validate the absorption testing results of thick carbon epoxy laminates. Design/methodology/approach The experimental results were validated by using a diffusion model in Abaqus FE code. Findings The absorption results of three 15 mm thick carbon epoxy laminates are presented and reproduced via a mass diffusion model. The laminates were conditioned at 70°C and 85 per cent relative humidity in a moisture chamber. Areas more prone to saturation have been predicted by the FE model and the moisture content in the non-saturated areas has been calculated. Practical implications The practical implications of the absorption model are discussed on an example of an aero-engine fan blade-like structure. Originality/value Validation of thick panels’ absorption data is an important point of novelty of this paper, given the lack of experimental and modelling validation in the open literature.

Progressive failure analysis of thick imperfect composite plates using nonlinear plate theory

The work presented here alludes to the application of a semi-analytical method for ultimate strength predictions of square composite plates with geometric imperfections that are subjected to uniaxial in-plane compressive load. The Ritz method is developed with the assumptions of large deflections and higher-order shear deformation theory that accounts for through-the-thickness deformation. Therefore, some thick and relatively thick simply-supported square laminates are analyzed in this study. To obtain the ultimate strength of the plates, we consider two geometric degradation models to assess the degradation zone around the failed location. To predict the first ply failure load and also nonlinear response in the progressive damage analysis, we use the Hashin–Rotem failure criteria. We present results with respect to the number of plies, thickness of the laminates and different magnitudes of imperfection for some symmetric lay-ups.

Derivation of a mesoscopic model for nonlinear particle-reinforced composites from a fully microscopic model

Particle-reinforced composites (PRCs) are usually studied by some averaging or homogenization techniques. In this, the effective properties are derived by assuming that particles are dispersed within composites according to some given (probabilistic) distribution. Such approaches restrain the possibilities of studying the contribution of exact location and parameters of individual particles to the overall behavior of composites. In this paper, we attempt to fill this gap by deriving the mesoscopic model of such composites corresponding to a continuum with point inhomogeneities. We start from a fully microscopic model where the composite is regarded as a continuum with spherical inclusions. Letting the diameter of inclusions decrease to zero, material parameters of the composite are represented in terms of the Dirac distribution. The Mindlin–Reissner–von Karman thick plate theory is considered as a particular case, and closed-form formulas are obtained for the plate stiffness coefficients. Numerical analysis of a thick composite plate reinforced over its mid-surface justifies the theoretical derivations.

Geometrically nonlinear analysis of time-dependent composite plates using time function optimization

In this paper, a novel approximation method is presented for the large deformation analysis of moderately thick fiber-reinforced composite plates based on elasticity responses at asymptotic times. The displacement vector is approximated using separation of variables, by two functions of geometrical parameters and one function of time parameter with unknown coefficients. The unknown coefficients of the time function are determined employing the least squares optimization and the Lagrange multipliers methods. It is shown that the geometrically nonlinear responses of time-dependent composite plates can be obtained by finding the optimum coefficients of the time function with low computational cost and high precision.

Microstructural Characterization and Mechanical Properties of 120-mm Ultra-thick SiCp/Al Composite Plates Joined by Double-Sided Friction Stir Welding

Applications of aluminum matrix composite (AMC) engineering components are being quickly developed and their numbers are increasing, but difficulties still exist in the direct fabrication of large AMC components. Joining thick composite plates without drawbacks has become an effective and alternative route, and friction stir welding (FSW) is the most promising and efficient technique, which should be selected first. In this work, 120-mm ultra-thick plates of 16 vol pct SiCp/2014Al composites were successfully joined by double-sided FSW. Microstructural characterization and mechanical properties of the composite joint along the transverse and thickness directions are investigated, respectively. Along the transverse direction changing from the base material (BM) to the heat-affected zone (HAZ) to the nugget zone (NZ), SiC particles are broken, blunted and uniformly distributed, and the aluminum grains are refined. The coarse precipitates are dissolved and then re-precipitated. Vickers microhardness of the composite joint gradually increases, and the peak values appear in the NZ. For the composite joint, the tensile strength is close to that of the BM showing a joint efficiency of 97 pct. Along the thickness direction varying from the top surface to middle section of the composite joint, the SiC particle size has no significant differences in the NZ, the aluminum grain size gradually decreases, and the precipitate size has some differences. Vickers microhardness of the composite joint decreases with increasing thickness in the NZ and HAZ, and no clear differences exist in the BM; tensile properties of the composite joint present few differences with varying thickness, and tensile failures usually occur in the BM. A good understanding and guide can be provided for joining ultra-thick plates of metal matrix composites by FSW in industrial applications.

Analytical modeling of bending and vibration of thick advanced composite plates using a four-variable quasi 3D HSDT

This work presents an efficient and original high-order shear and normal deformation theory for the static and free vibration analysis of functionally graded plates. The Hamilton’s principle is used herein to derive the equations of motion. The number of unknowns and governing equations of the present theory is reduced, and hence makes it simple to use. The present plate theory approach accounts for both transverse shear and normal deformations and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factor. Unlike any other theory, the number of unknown functions involved in displacement field is only four, as against five or more in the case of other shear and normal deformation theories. The accuracy of the proposed solution is checked by comparing it with other closed form solutions available in the literature.