三维间断位移法及强奇异和超奇异积分的处理方法

从积分方程Somigliana等式出发,导出三维状态下单位位错集度的基本解.在此基础上,建立了边界积分方程,并给出了其离散形式.对强奇异和超奇异积分,采用了Hadamard定义的有限部分积分来处理.最后,给出了计算裂纹应力强度因子的算例,并与解析解进行了比较,证实了该方法的有效性.     

蠕变裂隙扩展与岩石长时强度效应实验研究

本文对岩体强度弱化与裂隙蠕变断裂行为之间基本关系，应用实验手段，从宏观，细观等角度进行了对比研究，得到了裂隙岩体强度弱化与裂隙扩展过程之间的基本关系，为裂隙岩体蠕变稳定性分析提供了实验依据。     

考虑疲劳裂纹扩展三维效应的James—Anderson修正方法

James-Anderson方法是一种借助材料疲劳裂纹扩展速率性能来确定三维裂纹应力强度因子的重要实验方法。本文对James-Anderson方法中的疲劳裂纹扩展三维效应进行了分析，并对其进行修正。修正后的James-Anderson方法考虑了疲劳裂纹扩展中由于应力状态而引起的三维效应。研究结果表明：和James-Anderson方法相比，修正后的James-Anderson方法得到的应力强度因子和三维数值方法所得的应力强度因子更吻合。     

Effects of static electric field on the fracture behavior of piezoelectric ceramics

The paper gives an overview on experimental observations of the failure behavior of electrically insulating and conducting cracks in piezoelectric ceramics. The experiments include the indentation fracture test, the bending test on smooth samples, and the fracture test on pre-notched (or pre-cracked) compact tension samples. For electrically insulating cracks, the experimental results show a complicated fracture behavior under electrical and mechanical loading. Fracture data are much scattered when a static electric field is applied. A statistically based fracture criterion is required. For electrically conducting cracks, the experimental results demonstrate that static electric fields can fracture poled and depoled lead zirconate titanate ceramics and that the concepts of fracture mechanics can be used to measure the electrical fracture toughness. Furthermore, the electrical fracture toughness is much higher than the mechanical fracture toughness. The highly electrical fracture toughness arises from the greater energy dissipation around the conductive crack tip under purely electric loading, which is impossible under mechanical loading in the brittle ceramics. The project supported by an RGC grant from the Research Grant Council of the Hong Kong Special Administrative Region, China     

基于数字图像相关方法的不锈钢内部缺陷检测研究

不锈钢材料内部缺陷检测是无损检测领域的研究热点和难点之一,尤其对微小和闭合裂纹的检测.本文提出了一种基于数字图像相关方法的应变集中缺陷识别方法,即对试样表面采用曝光灯进行辐射加热,利用数字图像相关方法定量分析试样表面应变场,通过试样表面高应变区域的表征,实现对金属内部裂纹的检测.结果表明,该方法可以在试样加热过程中表征不锈钢内部裂纹,其有效检测深度可达3.71 mm.     

Electromagnetic MUSIC-type imaging of perfectly conducting, arc-like cracks at single frequency

We propose a non-iterative MUSIC (MUltiple SIgnal Classification)-type algorithm for the time-harmonic electromagnetic imaging of one or more perfectly conducting, arc-like cracks found within a homogeneous space R²${\mathbb{R}}^2$. The algorithm is based on a factorization of the Multi-Static Response (MSR) matrix collected in the far-field at a single, nonzero frequency in either Transverse Magnetic (TM) mode (Dirichlet boundary condition) or Transverse Electric (TE) mode (Neumann boundary condition), followed by the calculation of a MUSIC cost functional expected to exhibit peaks along the crack curves each half a wavelength. Numerical experimentation from exact, noiseless and noisy data shows that this is indeed the case and that the proposed algorithm behaves in robust manner, with better results in the TM mode than in the TE mode for which one would have to estimate the normal to the crack to get the most optimal results.     

Generalized Newton methods for crack problems with nonpenetration condition

A class of semismooth Newton methods for unilaterally constrained variational problems modeling cracks under a nonpenetration condition is introduced and investigated. On the continuous level, a penalization technique is applied that allows to argue generalized differentiability of the nonlinear mapping associated to its first‐order optimality characterization. It is shown that the corresponding semismooth Newton method converges locally superlinearly. For the discrete version of the problem, fast local as well as global and monotonous convergence of a discrete semismooth Newton method are proved. A comprehensive report on numerical tests for the two‐dimensional Lamé problem with three collinear cracks under the nonpenetration condition ends the article. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005     

Fracture of a biopolymer gel as a viscoplastic disentanglement process

We present an extensive experimental study of mode-I, steady, slow crack dynamics in gelatin gels. Taking advantage of the sensitivity of the elastic stiffness to gel composition and history we confirm and extend the model for fracture of physical hydrogels which we proposed in a previous paper (Nature Mater. 5, 552 (2006)), which attributes decohesion to the viscoplastic pull-out of the network-constituting chains. So, we propose that, in contrast with chemically cross-linked ones, reversible gels fracture without chain scission.     

Periodic cracks and temperature-dependent stress in Mo/Si multilayers on Si substrates

This work examines formation of the peculiar periodic crack patterns observed in the thermally loaded Mo/Si multilayers. Using the substrate curvature measurements, the macroscopic film stress evolution during thermal cycling was investigated. Then high-speed microscopic observation of crack propagation in the annealed Mo/Si multilayers was presented providing experimental evidence of the mechanism underlying formation of the periodic crack patterns. The origin of the peculiar periodic crack patterns was determined. They were observed to form by the slow crack propagation under quasi-static conditions as a result of the interaction between the channelling crack propagation and the advance of the delamination front.     

On the stored and dissipated energies in heterogeneous rate-independent systems: theory and simple examples

The aim of the present work is to determine the amount of dissipated and stored energies in structures containing frictional cracks and elasto-plastic zones. The proposed theory combines micromechanical and thermodynamic tools to calculate both energies. Using simple examples, it is shown that the Taylor–Quinney coefficient is not a constant, and can be much less than the values usually considered (i.e. close to unity).