Analysis of tongue and groove joints for thick laminates

A finite element evaluation of local stresses in the adhesive and adherends is presented for a tongue-and-groove joint of a homogenized thick composite laminate to steel plate. The quasi-isotropic laminate is made of glass fabric/vinyl ester plies. Most results are obtained for elastic response of the Dexter-Hysol 9338 adhesive that was used in recent experiments (Compos Sci Technol 61 (2001) 1123–1142). A non-linearly viscoelastic adhesive is also considered, with illustrative properties taken from experiments on the FM-73 system. Both in-plane force resultants and out-of-plane moments are included in the applied loads. Scaling of the elastic results with regard to plate thickness shows that for given levels of overall stresses applied to the adherend plates, the stresses supported by the adhesive do not depend on plate thickness. Adhesive stress relaxation is shown to be relatively small, and occurring in a short time period.     

复合材料加筋层合板的极限强度分析

基于更新拉格朗日格式,应用非线性层合三维退化壳元,结合有效的复合材料失效准则、刚度退化模型以及提出的刚度矩阵奇异判断准则,对复合材料加筋层合板在轴向载荷作用下的压缩极限强度问题进行深入研究。讨论了铺层方式、板厚等对极限强度的影响。通过与试验结果进行比较,表明基于提出的刚度矩阵奇异判断准则,结合增量更新拉格朗日格式下非线性层合三维退化有限元的计算方法,能有效计算复合材料加筋层合板的轴向压缩极限强度,并具有很高的精度。     

Stress Distributions around Holes in Composite Laminates Subjected to Biaxial Loading

An approximate solution has been derived for the in-plane stresses near a circular hole, in an orthotropic composite laminate under biaxial loading. The derived stresses were found to be in good agreement with the exact analytical solution, for a series of laminates investigated. However, the degree of accuracy of the approximate stress distribution is strongly influenced by the laminate lay-up and the biaxiality ratio. The resultant stresses could be employed in stress based fracture models to investigate the notch sensitivity and fracture mechanisms of composite plates with an open-hole subjected to biaxial loading.     

Distribution of shearing stresses in a composite beam under transverse loading

An approximate elasticity solution is derived for the transverse shearing stresses in a multilayered anisotropic composite beam. With this solution, the distribution of shearing stresses through the laminate thickness can be determined for any ply orientation and stacking sequence. Experimental data are shown to compare the theoretical and experimental strengths for beams of glass/epoxy and graphite/epoxy. It was found that experimental and theoretical strengths were in fairly good agreement for a strength theory which has been modified to predict ultimate laminate failure.     

Numerical plate testing for linear two‐scale analyses of composite plates with in‐plane periodicity

A method of numerical plate testing (NPT) for composite plates with in‐plane periodic heterogeneity is proposed. In the two‐scale boundary value problem, a thick plate model is employed at macroscale, while three‐dimensional solids are assumed at microscale. The NPT, which is nothing more or less than the homogenization analysis, is in fact a series of microscopic analyses on a unit cell that evaluates the macroscopic plate stiffnesses. The specific functional forms of microscopic displacements are originally presented so that the relationship between the macroscopic resultant stresses/moments and strains/curvatures to be consistent with the microscopic equilibrated state. In order to perform NPT by using general‐purpose FEM programs, we introduce control nodes to facilitate the multiple‐point constraints for in‐plane periodicity. Numerical examples are presented to verify that the proposed method of NPT reproduces the plate stiffnesses in classical plate and laminate theories. We also perform a series of homogenization, macroscopic, and localization analyses for an in‐plane heterogeneous composite plate to demonstrate the performance of the proposed method. Copyright © 2015 John Wiley & Sons, Ltd.     

Combining X-FEM and a multilevel mesh superposition method for the analysis of thick composite structures

The use of simultaneous multiple plate models offers an attractive and alternative solution to full scale three-dimensional finite element method for the global–local analysis of laminated composite structures. In this paper, an approach is proposed where the less accurate plate model, used to carry out the analysis at the global level, is enhanced by more accurate and complex plate models in each laminate subregion where more accurate transverse stress or strain estimation is required (the local level).The total displacement is represented as the superposition of the displacements of a number of plate models. By appropriately defining boundaries to the enhancing model/region, it is demonstrated that the superposition of displacements can be used to locally enrich the solution where accurate through-the-thickness stresses are required. In this manner, a computationally efficient global model can be used to determine gross displacements, and potentially the enriched models can be used to determine stresses at lamina interfaces for the accurate prediction of localized phenomena such as damage initiation and growth. The model is implemented combining an extended FEM (X-FEM) and multilevel mesh superposition approach (MMSA). Extra degrees-of-freedom are added to the model to represent the additional displacement fields, and the meshing process remains independent for each field.The displacements and stresses computed by this approach are compared to literature data and analytical solutions for various plate geometries and loads showing an excellent correlation. Morevoer, the results showed, as expected, that the accuracy of the approximation is improved by the proposed approach compared to using the global plate model alone.     

Interlaminar stresses in composite laminates: Thermoelastic deformation

An approximate elasticity solution for prediction of the displacement, stress and strain fields within the m-layer, symmetric and balanced angle-ply composite laminate of finite-width and subjected to uniform axial extension was developed earlier [4]. In the present paper, the authors have extended that solution to treat thermal stresses and deformations induced by a uniform change in laminate temperature. The results have revealed not only the complex fields within the laminate, but also inter-relationships between the lamina axial and shearing coefficients of thermal expansion and the effective laminate coefficients of thermal expansion. Further, the solution is shown to recover laminated plate theory predictions for thermally induced fields at interior regions of the laminate, thereby confirming the boundary layer nature of the interlaminar phenomena for the thermoelastic case. Finally, the results exhibit the anticipated response in congruence with the mechanical solution of Ref. [4] and the thermoelastic results satisfy the conditions of self-equilibration necessary for the finite-width laminate subjected to free thermal deformation. Integration of the stress σ_x over the laminate cross-section in the y–z plane is shown to converge to zero as the number of Fourier terms is increased. While the exact solution for mechanical loading is known to exhibit singular behavior, non-convergence of the interlaminar shearing strain is also seen to occur at the intersection of the free edge and planes between lamina of +θ and −θ orientation under thermal loading. The analytical results show excellent agreement with the finite-element predictions for the same boundary-value problem.     

Bending response of web-core sandwich beams

This paper presents a new analytical solution for the bending response of a web-core sandwich beam. The beam is a transverse cut from the sandwich plate. The method is based on the plane frame analysis, where the response of the beam is divided into local and global components. The Clebsch’s method is used to calculate the deflection of the face plates. The validation of the plane frame method is carried out with FE-analyses based on the shell element formulation. Also a comparison is made with the method based on homogenized beam. Periodic stress distributions in the face plates are revealed with the plane frame analysis and are supported by the FE-analysis. The existing methods based on homogenized beam are not able to predict these stresses. The plane frame analysis can benefit the development of the theory related to web-core sandwich plate.     

Out-of-plane stresses in composite shell panels: layerwise and elasticity solutions

Boundary-layer effects in lengthy cross-ply laminated circular cylindrical shell panels under uniform axial extension are investigated by two analytical solutions. First, Reddy??s layerwise theory with state-space approach is utilized to determine the local interlaminar stresses. In this method, the general displacement field is discretized through the shell thickness by a linear shape function. When the shell panel is subjected to an axial force, the axial strain is estimated by an equivalent single-layer theory. Second, the stress-function approach along with Fourier series expansion is applied to develop a novel elasticity solution. The elasticity solution, which is based on simply-support edge conditions, is presented to show the effectiveness of the first solution. The numerical results show good agreements. Interlaminar stresses within various symmetric and unsymmetric cross-ply composite shell panels are then calculated and discussed. It is shown that the normal out-of-plane stress can get high magnitudes along the physical interfaces.     

梯度功能材料板热弹性分析模型

建立了梯度功能材料板的热弹性分析模型。考虑到梯度功能材料的材料性能沿板厚变化,参照复合料层合板将其沿板厚分为若干层,当层数足够多时,各层材料性能可视为常值。通过引入温度沿板厚折线假设和在位移场中考虑截面翘曲,显著改善了这类问题解的精度。算例显示了文中模型的精度和已有分析方法的不足,讨论了分层数的选取。     

Effect of impact damages on the compressive strength of composite laminates

Abstract

By simplifying the impact damages as a single delamination near the surface with an elliptical boundary, the approximate solution of total strain energy release rates can be derived as a function of delamination major axis, minor axis, external compressive strain, Possion's ratio of parent medium, extensional and bending stiffnesses of sublaminate. A linear relation of residual strength versus strain energy release rate can be constructed by correlating the approximate solution with test data of compressive residual strain (strength) after impact (CSAI), indicating that the dimension between the delamination major and minor axis should be dependent. In addition, the delamination aspect ratio is found to be not only a function of the specimen geometry and the extensional stiffness, but also a function of laminate thickness. The approximate solution provides a method for predicting the post impacted strength of composite laminate for only either thick laminate or thin laminate with low impact energy.     

Stresses in a thick plate with a circular hole under axisymmetric loading

An exact theoretical solution is given for the stresses and displacements in an infinite plate of finite thickness having a circular hole and subjected to axisymmetric normal leading. The solution is given in the form of Fourier-Bessel series and integral. Numerical results are given for stresses in plates having different thickness to hole diameter ratios and loadings. The results are compared with the available approximate theoretical and experimental results.     

Multi-scale homogenization of moving interface problems with flux jumps: application to solidification

In this paper, a multi-scale analysis scheme for solidification based on two-scale computational homogenization is discussed. Solidification problems involve evolution of surfaces coupled with flux jump boundary conditions across interfaces. We provide consistent macro-micro transition and averaging rules based on Hill’s macro- homogeneity condition. The overall macro-scale behavior is analyzed with solidification at the micro-scale modeled using an enthalpy formulation. The method is versatile in the sense that two different models can be employed at the macro- and micro-scales. The micro-scale model can incorporate all the physics associated with solidification including moving interfaces and flux discontinuities, while the macro-scale model needs to only model thermal conduction using continuous (homogenized) fields. The convergence behavior of the tightly coupled macro-micro finite element scheme with respect to decreasing element size is analyzed by comparing with a known analytical solution of the Stefan problem.     

An exact Peano Series solution for bending analysis of imperfect layered functionally graded neutral magneto-electro-elastic plates resting on elastic foundations

In this article, a three-dimensional solution is presented for the bending analysis of functionally graded and layered neutral magneto-electro-elastic plates resting on two-parameter elastic foundations, considering imperfect interfacial bonding. The equations of motion, Gauss's equations for electrostatics and magnetostatics, and boundary and interface conditions are satisfied exactly regardless of the number of layers. No assumptions on deformations, stresses, and magnetic and electric fields along the thickness direction are introduced. The interfacial imperfection is modeled using a generalized spring layer. The state-space method is employed for solving the governing partial differential equations. Effects of a two-parameter elastic foundation, gradient index, bonding imperfection, and applied mechanical and electrical loads on the response of the functionally graded magneto-electro-elastic plate are discussed. The obtained exact solution can serve as a benchmark for assessing the accuracy of layered functionally graded magneto-electro-elastic plate theories.     

Analytical formulae for calculating stresses in unidirectional/cross-ply unbalanced laminates

A multilayer theory has been developed for unidirectional/cross-ply unbalanced laminates subjected to surface shear tractions, using the assumption of plane strain. The analytical solution for the stress field in the laminate is obtained and it is shown that the stresses in each layer are in good agreement with the results of a three-dimensional finite element analysis. Approximate formulae for the analytical stresses are also derived for a laminate subjected to an offset distributed force at one end. The accuracy of this solution is shown by comparison with a three-dimensional finite element analysis.     

Determination of residual shear stresses in composites by a modified layer-removal method

The layer-removal method is often used for measurement of internal stresses in homogeneous polymeric materials. In order to extend the use of the method to laminated composites containing shear stresses, certain refinements are needed. These include (i) determination of twisting moments, (ii) use of varying material properties (elastic moduli) through the thickness of the composite plate, (iii) use of geometric non-linear analysis accounting for large deformations, and (iv) measurement not only of normal curvatures but also twisting curvatures and normal and shear strains. These refinements are necessary, because a non-symmetric laminate is created when layers are removed, which shows large (twisting) curvatures. The modified layer-removal method was theoretically validated on a typical compression-moulded continuous fibre laminate (polyetherimide/glass) and a typical injection-moulded short fibre-reinforced laminate (polycarbonate/glass). The modified method produced good results and the need to use the modified layer-removal analysis is clearly demonstrated. © 1998 Chapman & Hall     

层板弯曲与振动的近似分析

横向剪切变形对复合材料层合板弯曲与振动的影响甚大。在本文的近似分析中,假定板在弯曲时横向位移沿整个板厚为常量。横向剪切应变沿各层厚度方向也分别为常量,但各层不同。文中以特殊正交各向异性层合板为例,采用两种不同的方法建立了各层剪切应变间的关系,推演了层合板横向弯曲与振动的微分方程组及边界条件。算例表明,即使层合板的跨——厚比很小,用本文两种分析方案计算位移、应力及固有频率,都仍具有较高的精度。      

Semi-analytical solution for orthotropic piezoelectric laminates in cylindrical bending with interfacial imperfections

The static and dynamic problems of an imperfectly bonded, orthotropic, piezoelectric laminate in cylindrical bending are investigated based on the equations of piezoelasticity. A general spring layer is adopted to model the bonding imperfection at the interfaces of the laminate. A recently proposed semi-analytical approach, which makes a hybrid use of the state-space method (SSM) and the differential quadrature method (DQM), is employed. This approach allows us to efficiently analyze the laminate with a large number of plies and with arbitrary boundary conditions at the two ends. Numerical examples are considered and discussed to show the efficiency of the present semi-analytical solution and the effects of relevant parameters on the behavior of the laminate.     

An efficient FE model and Least Square Error method for accurate calculation of transverse shear stresses in composites and sandwich laminates

Accurate evaluation of transverse stresses in laminated composites and sandwich plates using 2D FE models involves cumbersome post-processing techniques. In this paper a simple and efficient method has been proposed for accurate evaluation of through-the-thickness distribution of transverse stresses in composites and sandwich laminates by using a displacement based C⁰ FE model (2D) derived from Refined Higher Order Shear Deformation Theory (RHSDT) and a Least Square Error (LSE) method. The C⁰ FE model satisfies the inter-laminar shear stress continuity conditions at the layer interfaces and zero transverse shear stress conditions at the top and bottom of the plate. In this model the first derivatives of transverse displacement have been treated as independent variables to circumvent the problem of C¹ continuity associated with the above plate theory (RHSDT). The LSE method is applied to the 3D equilibrium equations of the plate problem at the post-processing stage, after in-plane stresses are calculated by using the above FE model based on RHSDT. Thus the proposed method is quite simple and elegant compared to the usual method of integrating the 3D equilibrium equations at the post-processing stage for calculation of transverse stresses in a composite laminate. In the proposed method, the first two equations of equilibrium are utilized to compute the transverse shear stress variation through the thickness of a laminated plate whereas the third equation of equilibrium gives the normal stress variation. Accuracy of the proposed method is demonstrated in the numerical examples through comparison of the present results with those obtained from different models based on higher order shear deformation theory (HSDT) and 3D elasticity solutions.