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。     

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。     

SiC纤维增强钛基复合材料界面研究及构件研制

首先介绍了作者近年来在SiC纤维增强钛基复合材料界面反应机理、应力分布和界面调控方面的工作进展,然后介绍了作者在磁控溅射法和箔-纤维-箔法复合材料工艺及构件研制方面的研究工作。     

Thermally induced logarithmic stress singularities in a composite wedge and other anomalies

Wedge paradoxes, which were first studied by Sternberg and Koiter (Sternberg E, Koiter WT. The wedge under a concentrated couple: a paradox in the two-dimensional theory of elasticity. ASME Journal of Applied Mechanics 1958;4:575–81), occur due to multiple roots in the Williams (Williams ML. Stress singularities resulting from various boundary conditions in angular corners of plates in extension. ASME Journal of Applied Mechanics 1952;19:526–28) eigenfunction expansion. The consequence of such a paradox is a change in behavior of the stresses from , to the ‘non-separable’ form,

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. The focus of this study is the problem of thermally induced logarithmic stress singularities in a composite wedge associated with ω=0. Both double and triple root examples are presented which lead to and behavior in the stresses, respectively. This behavior is primarily associated with incompressible materials for the clamped–clamped single material case, and for the full range of Poisson’s ratio for the clamped-free case. The study also includes non-separable eigenfunctions that occur when complex conjugate roots transition to double real roots. Perhaps the most interesting result is that for the clamped–clamped wedge with Poisson’s ratio equal to 1/2, the hydrostatic stress has a logarithmic singularity proportional to the thermal strain for all wedge angles. This result can be extended to conclude that for a confined, incompressible or nearly incompressible material with a relatively sharp corner, and subject to some expansion or contraction phenomena, high hydrostatic stresses can result.     

碳纤维增强镁基复合材料的界面研究进展

综合评述了碳纤维增强镁基复合材料的界面研究进展.介绍了碳纤维增强体的优点和两种不同的去胶方法,比较了不同的碳纤维涂层和基体成分对复合材料界面状态的影响,并对今后碳纤维增强镁基复合材料的研究方向进行了展望.     

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.     

Non‐oscillatory and non‐singular asymptotic solutions to stress fields at interface cracks

This work concerns the complex oscillatory singularities revealed in Williams's asymptotic solutions to stress fields around arbitrary interface cracks, which are the foundation of phenomenological interface fracture mechanics. First, we highlight the fatal discrepancy between the asymptotic stress fields for cracks in a homogeneous material obtained by assigning an identical material on both regions embracing an interface crack, and the solutions directly derived from cracks in a single material. Next, following a brief introduction to Williams's formulation process, we adopt the method of repeatedly eliminating variables instead of solving the determinant equation for the coefficient matrix to reformulate the asymptotic analysis of stress fields at arbitrary interface cracks. The resultant stresses get rid of oscillatory character. Further, under two specific loading conditions, namely, remotely uniaxial tension or shear, non‐oscillatory and non‐singular asymptotic solutions to stress fields around interface cracks are obtained.     

Al-Ni超声楔焊中输入功率与界面键合的特征分析

为了研究超声键合中在超声能量作用下金属间形成键合界面而构成键合力的机理,确定金属间吸收的超声能量与形成的界面质量的关系,在超声楔焊键合试验中,对Al-Ni楔焊通过改变焊接参数而获得完全键合和半键合的界面,并对其界面特征进行扫描电镜测试分析;同时,利用示波器采集超声键合机焊接时的电信号,分析了PZT驱动的输入阻抗和功率特性,并与界面质量对比.研究结果表明:超声键合而形成的Al-Ni界面为中央未键合的椭圆界面;相同参数条件下,一焊输入阻抗和吸收功率大于二焊,一焊的界面质量也高于二焊.     

碳纤维复合材料补强混凝土界面温度应力分析

碳纤维片材的热膨胀系数与混凝土的热膨胀系数相差很大,因而,在环境温差作用下,补强碳纤维片材和混凝土界面处将产生界面温度应力.正确地分析界面温度应力,揭示界面温度应力的变化规律,对补强结构设计和安全评价具有重要意义.建立了碳纤维片材补强混凝土梁的界面温度应力定量计算公式,并通过实验测试验证了定量分析理论的合理性.研究结果表明:界面温度应力分布及大小与补强复合材料的刚度和作用温差有较大关系,与基底混凝土的刚度关系不大.     

Improvement of the bonding interface in hybrid fiber/particle preform reinforced Al matrix composite

The bonding interface between the reinforcement and the matrix alloy in hybrid AZS fiber/SiC particle preform based aluminum metal matrix composites (Al MMCs) has been investigated as a function of reinforced particle size and the binder content. It is observed that high binder and large particle will result in a poor bonding interface. This has deleterious effects on the mechanical properties of the cast MMCs. Estimation of the binder thickness indicates that there exists a critical particle size above which the particles are not appropriate to be used in fabricating the hybrid fiber/particle preform based MMCs.     

An eigenfunction expansion solution for three-dimensional stress field in the vicinity of the circumferential line of intersection of a bimaterial interface and a hole

An asymptotic solution pertaining to the stress field in the neighborhood of the circumferential line of intersection of an interface of a two-layer plate made of dissimilar isotropic materials and a through-hole, subjected to far-field extension/bending (mode I), inplane shear-twisting (mode II) and torsional (mode III) loadings, is presented. A local orthogonal curvilinear coordinate system (, , ), is selected to describe the local deformation behavior of the afore-mentioned plate in the vicinity of the afore-mentioned circumferential line of intersection. One of the components of the Euclidean metric tensor, namely g ₃₃, is approximated (/a1) in the derivation of the kinematic relations and the ensuing governing system of three partial differential equations. Four different combinations of boundary conditions are considered: (i) open hole (free-free), (ii) hole fully filled with an infinitely rigid plug (clamped-clamped), (iii) hole partially (i.e., in the layer 2) filled with an infinitely rigid plug (free-clamped), and (iv) hole partially (i.e., in the layer 1) filled with an infinitely rigid plug (clamped-free). The computed eigenvalues for the clamped-free boundary condition can be obtained from their free-clamped counterparts by replacing G ₂ by G ₁ and ₂ by ₁, and vice versa. These two boundary conditions are then equivalent in the complementary sense. Numerical results presented include the effect of the ratio of the shear moduli of the layer materials, and also Poisson's ratios on the computed lowest eigenvalues.