基于Layerwise离散层理论的复合材料夹层板屈曲分析

复合材料夹层结构由于面板和芯层力学特性差异较大,屈曲分析时要分层考虑各层的剪切变形。基于Reddy的Layerwise离散层理论,假设每一层变形服从一阶剪切变形理论,在统一的位移场描述下,推导建立了一种用于复合材料夹层结构屈曲分析的四节点四边形板单元,并采用混合插值方法对单元的剪切锁定进行了修正。分别对三种典型的夹层板结构进行线性屈曲有限元分析,并将计算结果与文献中已有结果进行了对比。结果表明：本文的分析方法能离散考虑各层的力学特性,将结构离散为多层时,计算结果与三维弹性理论或高阶板理论吻合;将结构等效为单层时,计算结果与基于一阶剪切变形理论的文献结构吻合,验证了单元的有效性。     

Thermal buckling analysis of truss-core sandwich plates

Truss-core sandwich plates have received much attention in virtue of the high values of strength-to-weight and stifness-to-weight as well as the great ability of impulseresistance recently. It is necessary to study the stability of sandwich panels under the influence of the thermal load. However, the sandwich plates are such complex threedimensional(3D) systems that direct analytical solutions do not exist, and the finite element method(FEM) cannot represent the relationship between structural parameters and mechanical properties well. In this paper, an equivalent homogeneous continuous plate is idealized by obtaining the efective bending and transverse shear stifness based on the characteristics of periodically distributed unit cells. The first order shear deformation theory for plates is used to derive the stability equation. The buckling temperature of a simply supported sandwich plate is given and verified by the FEM. The efect of related parameters on mechanical properties is investigated. The geometric parameters of the unit cell are optimized to attain the maximum buckling temperature. It is shown that the optimized sandwich plate can improve the resistance to thermal buckling significantly.     

Coupled buckling and postbuckling analysis of active laminated piezoelectric composite plates

A theoretical framework for analyzing the pre- and postbuckling response of composite laminates and plates with piezoactuators and sensors is presented. The mechanics include nonlinear effects due to large rotations and stress stiffening, and are incorporated into a coupled mixed-field piezoelectric laminate theory. Using the previous mechanics, a nonlinear finite element method and an incremental-iterative solution are formulated for the analysis of nonlinear adaptive plate structures subject to in-plane electromechanical loading. A novel eight-node nonlinear plate finite element is also developed. Evaluation cases predict the buckling and postbuckling response of adaptive composite beams and plates with piezoelectric actuators and sensors. The case of piezoelectric buckling and postbuckling induced by the actuators is addressed and quantified. Finally, the possibility to actively mitigate the mechanical buckling and postbuckling response of adaptive piezocomposite plates is illustrated.     

Sandwich modeling with an application to the residual strength analysis of a damaged compression panel

Finite element models of sandwich structures are often based on classical sandwich theory which reduces the essentially three-dimensional composite — a combination of two high strength faces separated by a light weight core — to a two-dimensional, deformable reference surface to which certain appropriate stiffness properties against stretch, bending and transverse shear are attached.The simplification introduced in this way is well established, but it suffers from a number of drawbacks that restricts its range of applicability rather severely. The drawbacks concern among others, the kinematic and dynamic boundary conditions that prohibit a realistic application of the loading along the edges. They also concern the inability of this model to study local effects such as buckling of the faces.In the present paper, we demonstrate how, with a relatively simple means, a sandwich model can be introduced that does not suffer from the deficiencies mentioned above. Moreover, this improved model provides the possibility to study the detrimental effect of delamination of the faces, and/or, decohesion zones between the core and faces, on the buckling strength of sandwich compression panels.The modification proposed here makes use of existing shell finite elements that are standard in many finite element codes. These shell elements are used to model the deformation of the faces of the sandwich, while the coupling between the two shell components is carried out by applying an appropriate penalty function that represents the deformation of the core.In this paper, we describe this model in some detail and solve an example problem involving the buckling of a sandwich plate with a partially debonded face plate.     

Buckling analysis of sandwich plates with FGM face sheets resting on elastic foundation with various boundary conditions: an analytical approach

This paper presents an analytical investigation on the buckling analysis of symmetric sandwich plates with functionally graded material (FGM) face sheets resting on an elastic foundation based on the first-order shear deformation plate theory (FSDT) and subjected to mechanical, thermal and thermo-mechanical loads. The material properties of FGM face sheets are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. An analytical approach is used to reduce the governing equations of stability and then solved using an analytical solution which is named as power series Frobenius method for symmetric sandwich plates with six different boundary conditions. A detailed numerical study is carried out to examine the influence of the plate aspect ratio, side-to-thickness ratio, loading type, sandwich plate type, volume fraction index, elastic foundation coefficients and boundary conditions on the buckling response of FGM sandwich plates. This has not been done before and serves to fill the gap of knowledge in this area.     

含分层损伤复合材料层合板的压缩强度研究

给出了基于一阶剪切变形理论的含分层损伤层合板有限元分析模型,将含分层损伤层合板在压缩载荷作用下的强度破坏分析和屈曲破坏分析统一起来。先区分其破坏形式,然后再进行具体破坏分析,在屈曲特性分析中考虑了铺层强度破坏引起的刚度折减的影响,数值结果表明,该文给出的方法和结论对含分层损伤复合材料层合板的设计更具参考价值。     

Response and Damage Tolerance of Composite Sandwich Structures under Low Velocity Impact

The deformation and failure response of composite sandwich beams and panels under low velocity impact was reviewed and discussed. Sandwich facesheet materials discussed are unidirectional and woven carbon/epoxy, and woven glass/vinylester composite laminates; sandwich core materials investigated include four types of closed cell PVC foams of various densities, and balsa wood. Sandwich beams were tested in an instrumented drop tower system under various energy levels, where load and strain histories and failure modes were recorded for the various types of beams. Peak loads predicted by spring-mass and energy balance models were in satisfactory agreement with experimental measurements. Failure patterns depend strongly on the impact energy levels and core properties. Failure modes observed include core indentation/cracking, facesheet buckling, delamination within the facesheet, and debonding between the facesheet and core. In the case of sandwich panels, it was shown that static and impact loads of the same magnitude produce very similar far-field deformations. The induced damage is localized and is lower for impact loading than for an equivalent static loading. The load history, predicted by a model based on the sinusoidal shape of the impact load pulse, was in agreement with experimental results. A finite element model was implemented to capture the full response of the panel indentation. The investigation of post impact behavior of sandwich structures shows that, although impact damage may not be readily visible, its effects on the residual mechanical properties of the structure can be quite detrimental.     

ON RESIDUAL COMPRESSIVE STRENGTH PREDICTION OF COMPOSITE SANDWICH PANELS AFTER LOW-VELOCITY IMPACT DAMAGE

This paper introduces a nonlinear finite element analysis on damage propagation behavior of composite sandwich panels under in-plane uniaxial quasi-static compression after a low velocity impact. The major damage modes due to the impact, including the residual indentation on the impacted facesheet, the initially crushed core under the impacted area, and the delamination are incorporated into the model. A consequential core crushing mechanism is incorporated into the analysis by using an element deactivation technique. Damage propagation behavior, which corresponds to those observed in sandwich compression after impact (SCAI) tests, has been successfully captured in the numerical simulation. The critical far field stress corresponding to the onset of damage propagation at specified critical locations near the damage zone are captured successfully. They show a good correlation with experimental data. These values can be used to effectively predict the residual compressive strength of low-velocity impact damaged composite sandwich panels.     

Buckling and post-buckling of laminated composite plates

This paper addresses the buckling and post-buckling of laminated composite plates using higher order shear deformation theory associated with Green–Lagrange non-linear strain–displacement relationships. All higher order terms arising from nonlinear strain–displacement relations are included in the formulation. The present plate theory satisfies zero transverse shear strain conditions at the top and bottom surfaces of the plate in von Karman sense. A C⁰ isoparametric finite element is developed for the present nonlinear model.     

夹层梁总体屈曲及皱曲的有限元计算

皱曲是夹层结构的一种短波屈曲模式,通常发生于夹心较厚或夹心刚度较低的情况。由于模型规模的限制,在常规有限元建模时通常将夹层板模拟为二维板单元,这种方法忽略了面板和夹心在厚度方向上的相互作用,无法计算出皱曲模式。针对上述问题,本文首先介绍了一个计算夹层结构总体屈曲和皱曲的统一理论,并将此理论的计算结果作为理论解。为了同时...