轴对称界面端的扭转问题

基于弹性力学轴对称扭转问题的通解,研究了具有任意几何形状的双材料轴对称界面端,给出了界面端的应力奇异性及其附近的位移场和奇应力场,定义了扭转问题的Ｄｕｎｄｕｒｓ双材料参数。研究结果表明,应力奇异性只与界面端的结合角和扭转问题的Ｄｕｎｄｕｒｓ双材料参数有关,而与界面的角度以及界面端与对称轴之间的距离无关,在任何情况下,特征值均为实数,不会产生振荡应力奇异性。     

结合材料界面端的三维应力奇异性

本文利用特殊有限元方法，开发了一个用来求解结合材料界面端三维应力奇异性问题的数值分析程序。该方法只需对界面端的角度方向进行离散即可求得应力奇异性。结合材料的应力奇异性取决于两种材料的材料常数和界面端形状。选用三个材料参数作为变量，用来研究结合材料三维应力奇异性随材料常数的变化规律。文中计算了几种重要而且常见的情况，并以此为基础建立了数据库。同时，还分析了应力奇异性随界面端形状的变化规律，并得到了应力函数的分布图。     

瞬态热冲击下层合材料板界面的热弹性行为

基于带有两个热松弛时间的G-L广义热弹性理论, 利用有限元方法研究了零阻抗理想界面层合板在瞬态热冲击诱导的位移、应力和温度等通过界面时的热弹性行为. 通过比较不同层中材料的比热容、热导系数、热松弛时间和密度等对界面处的位移、应力和温度的影响, 研究了不同材料参数对复合材料热力学行为影响, 发现不同材料参数将导致热穿过界面时界面处温度、位移和应力发生突变, 研究结果可以为由热引起的层合板挠曲变形提供理论依据.      

纤维与基体的轴对称界面端附近的奇异应力场

基于各向性弹性力学空间轴对称问题的基本方程,研究了纤维与基体的轴对称界面端的应力奇异性,并给出了界最佳 近的奇异应力场。研究结果表明,该轴对称界面端的应力奇异性与平面应变状态下相应模型的应力奇异性完全相同,材料对界面端附近奇异应力场的影响可用丰个双材料组合参数描述。     

功能梯度压电/压磁双材料的周期界面裂纹问题

研究反平面载荷作用下压电/压磁双材料的周期界面裂纹问题,压电/压磁双材料由有限厚度的功能梯度压电层和功能梯度压磁层粘结而成.为便于分析,假设压电层和压磁层的材料性质沿着裂纹的法线方向呈指数变化,基于分离变量和Hilbert核奇异积分方程方法,获得应力强度因子的数值解.数值算例讨论层厚、周期带长度、梯度参数以及材料参数变动等对应力强度因子的影响.结果发现层厚以及裂纹间距的增大会降低裂纹尖端应力强度因子,梯度参数的改变对应力强度因子也有显著的影响.材料参数变动的讨论发现弹性参数的变动对应力强度因子影响最大,其次为电参数,磁参数的变动对应力强度因子影响最小.     

幂硬化弹塑性-刚性界面Ⅲ型定常扩展裂纹尖端的渐近场

对幂硬化弹塑性材料－刚性材料界面上裂纹以定常方式扩展的Ⅲ型问题进行弹塑性渐近分析，给出裂纹尖端的应力，应变和位移场解。通过数值计算，考察了不同Mach数以及裂纹尖端混合参数对场解的构造以及应力，应变分布的影响，为给出合理的断裂准则提供理论依据。     

直角结合异材界面端应力强度系数的经验公式

由不同材料结合而成的材料(简称异材或双材料)的力学性能及其可靠性评价是工程中亟待解决的问题。表征界面端奇异应力场大小的应力强度系数是结合异材强度评价的依据，本文针对工程中最常见的直角结合异材，通过对大量不同材料组合的异材的边界元数值分析，提出了界面端应力强度系数的近似计算公式，无量纲化后的应力强度系数的值只与异材Dundurs参数a，卢有关，该公式具有较高的精度，可以作为一般工程上的应力强度系数的计算以及异材结构设计的依据。     

多层电子器件的界面应力及塑性发展分析

界面应力是判断界面失效的关键参数,因此准确地预测界面应力对多层电子器件的设计具有重要意义.多层电子器件的层间界面处会出现较大的应力集中,引起结构发生塑性变形,而塑性区域的存在会改变应力集中程度,影响界面应力的分布,几何非线性和材料塑性的联合作用又会导致界面应力呈现不一样的奇异性.本文综合考虑弹塑性变形和几何非线性,对多层电子器件的界面应力分布及塑性区域发展进行了分析.以三层电子器件为例,详细讨论了电子器件在角位移加载和线位移加载两种模式下,界面应力分布和塑性区域的发展规律.相关结论可用于改善多层电子器件的工业设计.     

有限尺寸下双材料界面附近裂纹位置对裂纹尖端的影响

随着复合材料的应用和发展,不同材料组成的界面结构越来越受到人们的重视。界面层两侧材料的性能相异会引起材料界面端奇异性,同时界面和界面附近存在裂纹会引起裂尖处的应力奇异性。因此双材料界面附近的力学分析是比较复杂的。本文建立双材料直角界面模型,在材料界面附近预设初始裂纹,计算了有限材料尺寸对界面应力场及其附近裂纹应力强度因子的影响。运用弹性力学中的 Goursat 公式求得直角界面端在有限尺寸下的应力场以及其应力强度系数。通过叠加原理和格林函数法进一步得到在直角界面端附近的裂纹尖端应力强度因子。计算结果表明,在适当范围内改变材料内裂纹与界面之间的距离,界面附近裂纹尖端的应力强度因子随着裂纹与界面距离的增加而减少,并且逐渐趋于稳定。分析结果可以为预测双材料结构复合材料界面失效位置提供参考。     

不同压电介质界面上的反平面运动裂纹

利用积分变换技术,得到不同压电介质界面上的平面运动裂纹问题的分析解。结果表明应力及电位移强度因子均与界面裂纹扩展速度及材料参数相关,这不同于均匀压电介质中运动裂纹的结论,当两种压电介质完全相同时,本文结果将退化为均匀压电介质中反平面运动裂纹问题的解。     

基于分子动力学的结合材料界面破坏准则

结合材料的破坏通常都是从界面或其附近发生的,但界面破坏的机理及其评价准则尚未十分清楚.采用分子动力学模拟方法,可以对结合材料的界面破坏过程进行模拟,从而获得结合材料的界面应力和界面破坏之间的关系.界面破坏可以分为奇异应力场作用下的破坏,和界面应力集中引起的破坏两种.虽然在分子动力学模拟中采用了高度简化的界面模型,但对界面破坏过程的模拟,仍可以帮助人们获得结合材料界面破坏过程的规律性认识.分别模拟远场作用下界面上存在初始裂纹和界面附近存在初始裂纹两种情况下的界面破坏,根据分子动力学模拟结果,提出了一个结合材料界面破坏的准则.     

Elliptical inclusion in an anisotropic plane: non-uniform interface effects

We study the plane deformation of an elastic composite system made up of an anisotropic elliptical inclusion and an anisotropic foreign matrix surrounding the inclusion. In order to capture the influence of interface energy on the local elastic field as the size of the inclusion approaches the nanoscale, we refer to the Gurtin-Murdoch model of interface elasticity to describe the inclusion-matrix interface as an imaginary and extremely stiff but zero-thickness layer of a finite stretching modulus. As opposed to isotropic cases in which the effects of interface elasticity are usually assumed to be uniform (described by a constant interface stretching modulus for the entire interface), the anisotropic case considered here necessitates non-uniform effects of interface elasticity (described by a non-constant interface stretching modulus), because the bulk surrounding the interface is anisotropic. To this end, we treat the interface stretching modulus of the anisotropic composite system as a variable on the interface curve depending on the specific tangential direction of the interface. We then devise a unified analytic procedure to determine the full stress field in the inclusion and matrix, which is applicable to the arbitrary orientation and aspect ratio of the inclusion, an arbitrarily variable interface modulus, and an arbitrary uniform external loading applied remotely. The non-uniform interface effects on the external loading-induced stress distribution near the interface are explored via a group of numerical examples. It is demonstrated that whether the nonuniformity of the interface effects has a significant effect on the stress field around the inclusion mainly depends on the direction of the external loading and the aspect ratio of the inclusion.     

Cohesive fracture simulation and failure modes of FRP–concrete bonded interfaces

A work-of-fracture method using three-point bend beam (3PBB) specimen, commonly employed to determine the fracture energy of concrete, is adapted to evaluate the mode-I cohesive fracture of fiber reinforced plastic (FRP) composite–concrete adhesively bonded interfaces. In this study, a bilinear damage cohesive zone model (CZM) is used to simulate cohesive fracture of FRP–concrete bonded interfaces. The interface cohesive process damage model is proposed to simulate the adhesive–concrete interface debonding; while a tensile plastic damage model is used to account for the cohesive cracking of concrete near the bond line. The influences of the important interface parameters, such as the interface cohesive strength, concrete tensile strength, critical interface energy, and concrete fracture energy, on the interface failure modes and load-carrying capacity are discussed in detail through a numerical finite element parametric study. The results of numerical simulations indicate that there is a transition of the failure modes controlling the interface fracture process. Three failure modes in the mode-I fracture of FRP–concrete interface bond are identified: (1) complete adhesive–concrete interface debonding (a weak bond), (2) complete concrete cohesive cracking near the bond line (a strong bond), and (3) a combined failure of interface debonding and concrete cohesive cracking. With the change of interface parameters, the transition of failure modes from interface debonding to concrete cohesive cracking is captured, and such a transition cannot be revealed by using a conventional fracture mechanics-based approach, in which only an energy criterion for fracture is employed. The proposed cohesive damage models for the interface and concrete combined with the numerical finite element simulation can be used to analyze the interface fracture process, predict the load-carrying capacity and ductility, and optimize the interface design, and they can further shed new light on the interface failure modes and transition mechanism which emulate the practical application.     

双层金属纳米板界面能密度的尺寸效应

界面能密度是表征纳米复合材料与结构界面力学性质的重要物理量.采用分子动力学方法计算了不同面心立方金属晶体构成的双材料纳米薄板结构的界面能密度,分析了界面晶格结构形貌变化及界面效应对原子势能的影响.结果表明:双材料纳米薄板界面具有周期性褶皱状疏密相间的晶格结构形貌,界面上原子势能亦呈现周期性分布特性,而靠近界面的两侧原子势能与板内原子势能具有明显差异.拉格朗日界面能密度和欧拉界面能密度均随双层薄板厚度的增加而增加,最终趋向于块体双材料结构的界面能密度.     

内聚力界面单元与复合材料的界面损伤分析

推导了一种基于内聚力模型无厚的界面单元,用来模拟复合材料纤维与基体之间的界面层．研究了纤维周期分布的复合材料受横向荷载时,在界面不同的强韧性条件下其界面损伤演化的规律和对复合材料整体性质的影响     

Analysis of a mode-I crack perpendicular to an imperfect interface

The elastostatic problem of a mode-I crack embedded in a bimaterial with an imperfect interface is investigated. The crack is in proximity to and perpendicular to the imperfect interface, which is governed by linear spring-like relations. The Fourier transform is applied to reduce the associated mixed-boundary value problem to a singular integral equation with Cauchy kernel. By numerically solving the resulting equation, stress intensity factors near both crack tips are evaluated. Obtained results reveal that the stress intensity factors in the presence of the imperfect interface vary between that with a perfect interface and that with a completely debonding interface. Moreover, an increase in the interface parameters decreases the stress intensity factors. In particular, when crack approaches to the weakened interface closer, the stress intensity factors become larger for a sliding interface, and become larger or smaller for a Winkler interface, depending on the crack lying in a stiffer or softer material. The influences of the imperfection of the interface on the stress intensity factors for a bimaterial composed of aluminum and steel are presented graphically.     

A piezoelectric screw dislocation interacting with an imperfect piezoelectric bimaterial interface

A general method is presented for the analytical solution of a piezoelectric screw dislocation located within one of two joined piezoelectric half-planes. The bonding along the half-plane is considered to be imperfect with the assumption that the imperfect interface is mechanically compliant and dielectrically weakly (or highly) conducting. For a mechanically compliant interface tractions are continuous but displacements are discontinuous across the imperfect interface. In this context, jumps in the displacement components are assumed to be proportional to their respective interface traction components. Similarly, for a dielectrically weakly conducting interface the normal electric displacement is continuous but the electric potential is discontinuous across the interface. The jump in electric potential is proportional to the normal electric displacement. In contrast, for a dielectrically highly conducting interface the electric potential is continuous across the interface whereas the normal electric displacement has a discontinuity across the interface which is proportional to a certain differential expression of the electric potential. Explicit expressions are derived for the complex field potentials. The results show that there are two dimensionless parameters measuring the interface “rigidity” as compared to one for the purely elastic case. When the imperfect interface is compliant and weakly conducting, the two dimensionless parameters can be positive real values or complex conjugates with positive real parts. When the imperfect interface is compliant and highly conducting the two dimensionless parameters can only be positive real values. An expression for the image force acting on the screw dislocation due to its interaction with a compliant and weakly conducting interface is also given. It is found that the image force is only dependent on two dimensionless generalized Dundurs constants as well as two dimensionless parameters measuring the interface “rigidity”.     

具有分形结构界面的固体膜/粘滞层/基底层状结构的变形

考虑固体膜/粘滞层/基底结构中粘滞层/基底界面不平整对结构的稳定性,特别是固体薄膜稳定时的褶皱变形产生的影响.考虑自仿射和峰状的粗糙界面.自仿射的粗糙界面由振幅和分形维表征,振幅和分形维越大对结构平衡的影响越大;峰状界面由振幅和平均峰间距表征,振幅越大对结构平衡影响越大,平均峰间距越小对结构平衡影响越大.进而,用有限元方法模拟分析该结构,得到界面平整和不平整两种情况下固体膜面内失稳力.结果表明,粘滞层/基底不平整情况下结构的平衡状态与假设该界面为理想平整面所得的结果有很大不同,在结构尺寸较小的情况下不可假设该界面为理想平整来考察该结构的稳定性.     

界面裂纹萌生与扩展的分子动力学模拟

运用分子动力学模拟方法研究了裂纹在界面端处萌生与沿界面扩展的临界条件. 模拟考虑了一双相材料的3种模型，即构成90°/90°和 90°/180°夹角的两个界面端和一个界面裂纹. 模拟采用了包含原子区域与连续区域的并发型多尺度模型，即在界面端尖端和裂纹尖端附近 采用分子动力学(MD)方法，MD区域之外则按照线弹性有限元方法分析. 结果表明，在断裂启动时刻，3个模型沿界面的最大应力均达到界面理想强度；而且，其界 面能恰好足以克服界面材料的本征内聚能. 因此，界面端裂纹萌生与沿界面扩展的断裂条件可以通过界面理想强度和内聚能联系起来. 并基于模拟计算结果提出了界面断裂启动的统一准则.     

Interface damage modeled by spring boundary conditions for in-plane elastic waves

In-plane elastic wave propagation in the presence of a damaged interface is investigated. The damage is modeled as a distribution of small cracks and this is transformed into a spring boundary condition. First the scattering by a single interface crack is determined explicitly in the low frequency limit for the case of a plane wave normally incident to the interface. The transmission at an interface with a random distribution of small cracks is then determined and is compared to periodically distributed cracks. The cracked interface is then described by a distributed spring boundary condition. As an illustration the dispersion relation of the first modes in a thick plate with a damaged interface in the middle is given.