压电与导体双材料界面端的奇异性研究

提出了一种求解平面应变条件下横观各向同性压电与导体双材料界面端的应力及电位移奇异性的特征值法。基于横观各向同性压电材料的基本方程和一阶近似假设,利用分离变量形式的位移函数和电势函数,导出了关于应力和电位移奇异性指数的奇异性特征方程。求解由无网格法离散的特征方程,即可得到应力和电位移的各阶奇异性指数,同时还可得到相应的应力和电位移角函数。数值计算结果与文献中给出的结果非常吻合,表明该方法具有很高的精度和效率。     

双材料界面端附近奇异应力场消除几何条件研究

基于Bogy特征值方程,分析了消除界面端奇异应力场的几何条件,给出了平面应力和平面应变条件下的接合角组合曲线.应用有限单元法对上述结果进行了验证,并对消除应力奇异性后的界面应力进行了分析与讨论;结果表明:采用刚好使奇异性消失的接合角会获得最均匀的界面应力分布.     

铆接界面端三维奇异性应力场的研究

针对铆接结构的特点,应用特征函数扩展技术分析柱坐标下接触界面端的应力奇异性问题。建立了柱坐标下圆柱体端面接触边缘附近的三维渐近位移场和应力场渐近表达式,并根据铆钉/被铆接件接触界面端的位移和应力边界条件,建立一个非线性特征方程组。据此方程组可求解界面端邻域的应力奇异性指数、位移和应力角分布函数的数值解。通过与有限元方法计算结果相对比,验证了该方法的有效性。分析了平头、沉头以及半圆头铆钉构成的铆接结构的应力奇异性问题,考察了铆钉材料、几何形式和摩擦系数对接触界面端应力奇异性指数和应力场角分布的影响。     

纤维增强热塑性树脂基复合材料界面研究进展

纤维增强热塑性树脂基复合材料具有优良的耐化学药品性、生产周期短、可二次加工等特点,克服了热固性树脂基复合材料韧性差,断裂延伸率低,易发生早期应力开裂等缺点,可在使用环境苛刻,承载能力要求高的场合得到应用.本文从复合材料界面设计思想入手,评述了纤维/热塑性复合材料界面的最新研究进展,并结合剪滞法对微复合材料的界面测试方法进行了分析讨论.     

纤维增强复合材料中纤维的界面分离

提出了一种解析模型来预测由纤维剥离导致断裂时纤维增强复合材料的极限抗拉强度。解析分析是基于在出现纤维－基质界面处的破裂时断裂力学中的顺从方法。在下面假设的基础上建立模型：基质与纤维都表现弹性，且远离基质－纤维界面的区域处的基质应变等于复合材料应变。此外，假定纤维与基质间存在完全粘合且断面是无附着的。证明了对于存在或不存在界面破裂的情况，可获得纤维增强复合材料的分离应变能量释放率，提供了数值例子，且     

界面相性态对纤维增强复合材料内应力传递的影响

本文用有限元方法,计算分析了办面相性态对纤维增强复合材料内纤维与机体的界面间应力传递的影响。分析结果表明,界面刚度系数是纤维增强复合材料内纤维与机体的界面间应力传递的主要影响因素。     

曲线纤维增强复合材料圆环板的非轴对称弯曲问题

由自动铺丝机制造的结构具有面内变刚度特征。这种由空间变化引起的刚度变化使结构的控制方程成为了变系数偏微分方程,给求解非轴对称弯曲问题带来了很大挑战,难以求解其精确解。该文基于经典板壳理论,推导了柱坐标下正交各向异性变刚度圆环板非轴对称弯曲问题的控制方程。假定刚度分别随弹性模量指数函数和曲线纤维方向角连续变化,采用加权残值法计算了周边弹性约束时复合材料圆环板的挠度。通过与精确解结果的比对,验证该方法是有效的,并有较高精度。计算结果表明曲线纤维方向角的变化将使曲线纤维增强复合材料结构的相关力学性能明显优于同等比例的直线纤维增强复合材料结构。同时,结果还表明变刚度复合材料圆环板的非轴对称挠度与其周边的约束条件、材料参数、内外半径比值、纤维方向角等密切相关。     

几种常见荷载作用下横观各向同性地基轴对称问题的解析解

通过对各向同性弹性体力学中拉甫位移函数重新修正,应用位移解法,利用Hankel积分变换理论,在象域内得到横观各向同性地基的通解,运用汉克尔积分反演变换得到了半无限地基在几种常见荷载(圆形均布、集中力、刚性承载板)作用下的应力和位移解析解,并给出了数值计算结果。     

纤维增强聚合物基复合材料的界面性能

针对纤维增强聚合物基复合材料的界面性能，系统阐述了其界面层的结构和作用机理，详细介绍了界面结晶效应对力学性能的影响及界面性能的表征方法，最后论述了几种有效的纤维表面改性方法及改性效果。     

Three-Dimensional Thermo-Electro-Elastic Field in a Circular Plate of Functional Graded Materials with Transverse Isotropy

This article presents a set of axisymmetric solutions for a circular plate of functional graded materials with transverse isotropy subjected to uniform thermal loadings on the upper and lower surfaces. The temperature field in the plate is obtained as a prior, by integration. A direct displacement method is then employed to explicitly derive the thermo-electro-elastic field induced by the thermal loadings. Numerical calculations are carried out to validate the present results and to show the effect of material heterogeneity on the distributions of the coupled field. Some interesting phenomena have been observed.     

Analysis of Bimaterial Wedges Using a New Singular Finite Element

This paper is concerned with the singular stress field at the vertex of a bimaterial wedge under in-plane loading. The boundary value problem is initially formulated in terms of the complex function method. The eigenequations are obtained using the continuity conditions along the interface and the traction-free conditions along the free edges, leading to the development of explicit expressions for the singular stress and displacement fields for a general bimaterial wedge. These expressions are then used to develop a new singular finite element. This element enables the determination of the singular stress field and the associated stress intensity factors reliably and efficiently. To establish the validity of the method, test cases are examined and compared with existing solutions. The method is then applied to evaluate the effect of the wedge geometry and the elastic mismatch upon the resulting stress intensity factors.     

横观各向同性土介质与结构物共同作用的有限元与边界元耦合分析

本文采用有限元与边界元耦合方法对上与结构物进行共同作用的分析。其中上部结构采用有限元子结构法,地基上考虑为横观各向同性特性,应用边界元法,通过基础界面上位移连续、面力平衡的条件进行耦合分析。编制了相应的计算程序,对某高层空间剪力培与地基的共同作用进行了计算,与有限元法和实测结果进行了对比分析,得到了满意的结果。说明:有限元和边界元的耦合方法能充分发挥两者的优越性,不失为共同作用分析的一种有效途径。     

Singularities near three-dimensional corners in composite laminates

The high interlaminar stresses, which appear in laminated composites due to the boundary layer effect near the free edge, play an important role in the analysis and design of advanced structures. Moreover, they are also the dominant effect causing delamination. Even if the singular behavior of such structures is investigated in many works, most of them deal either with 2D, or with pseudo-3D problems, i.e. problems of two variables in a three-dimensional space. However, some numerical and experimental findings indicate that laminated plates exhibit a tendency to delaminate at corners, an effect impossible to be determined by a two-dimensional analysis. The aim of the present paper is to investigate stress singularities in a laminated composite wedge under consideration of real three-dimensional corner effects. A weak formulation, as well as a finite element approximation technique introduced in the past for isotropic problems is extended here to cover anisotropic material properties. This formulation leads to a quadratic eigenvalue problem, which is solved iteratively using the Arnoldi method. The first singular terms in the asymptotical expansion of the linear-elastic solution near the vertex of the wedge are obtained as eigenpairs of this eigenvalue problem. The order and mode of singularity are reported for all wedge angles and different fiber orientations for angle and cross-ply laminates. All calculations are based on a typical for some high modulus graphite-epoxy systems orthotropic material model.     

各向异性复合材料尖劈的应力奇异性次数研究

为了确定各向异性复合材料尖劈的应力奇异性次数,提出了一种确定广义平面应变情况下各向异性弹性接合材料界面端应力奇异性次数的一维特殊有限元法。该方法基于最小势能原理,通过坐标变换和变量分离消除径向坐标,把应力奇异性次数的求解降阶为仅与环向坐标相关的一维问题。采用三节点一维等参数二次单元,对该一维线性领域做网格划分。数值计算结果与理论解比较,表明该方法具有很高的精度和效率。     

The impact response of a half plane crack in a transversely isotropic solid due to 3-D mixed mode loading

Three-dimensional analysis of a half plane crack in a transversely isotropic solid is performed. The crack is subjected to two opposed pairs of shear line loads on its faces. Transform methods are used to reduce the boundary value problem to a set of coupled integral equations that can be solved by the Wiener-Hopf technique. The Cagniard-de Hoop method is employed to invert the transforms. Exact expressions are derived for the mode II and III stress intensity factors as functions of time and position along the crack edge. Some features of the solutions are discussed through numerical results.     

Singular Thermal Residual Stress Field near the Interface Corner of Bonded Dissimilar Materials

In this paper, a cooled composite interface corner consisting of two bonded dissimilar materials is considered as a plane problem. With the complex variable method, the thermal residual stress field is studied analytically. It is found that the regular stress term possesses the singularity either of lnr or ln²r. The exact expressions for the corresponding singular stress field are presented.     

Stress singularities in composite wedge-shaped materials

Calculations of the stress singularity in the vicinity of the tip of two bonded wedges are described. Plasticity in the near-tip region is accounted for within the framework of the Ramberg–Osgood relation. It is shown that the singularity can be larger for two bonded wedges than for a single wedge, and figures are presented to indicate how the stress singularity depends on the relevant parameters.     

横观各向同性层合压电矩形板稳定问题的三维精确分析

从横观各向同性压电弹性力学的三维基本方程出发,通过引入位移函数和应力函数,构造了两类相互独立的状态空间方程,使原方程解耦成两个低阶方程,有利于具体问题的求解。对于四边简支压电层合矩形板面内双向均匀受压的稳定问题,建立了层合板上下表面状态变量间的关系式,利用边界条件进一步导出特征方程。发现存在两类彼此无关的稳定形式:第一类对应板的纯面内稳定,而第二类则是一般意义上的板的弯曲稳定。给出了数值结果,并考察了相关参数的影响。