EFFECTS OF DISLOCATION CONFIGURATION, CRACK BLUNTING AND FREE SURFACES ON THE TRIGGERING LOAD OF DISLOCATION SOURCES

The effects of dislocation configuration,crack blunting and free surfaces on the triggering load of dislocation sources in the vicinity of a crack or a wedge tip subjected to a tensile load in the far field are investigated.An appropriate triggering criterion for dislocation sources is proposed by considering the configurational forces acting on each dislocation.The triggering behaviors of dislocation sources near the tips of a crack and a wedge are compared.It is also found that the blunting of crack tip and the presence of free surfaces near the crack or the wedge have considerable influences on the triggering load of dislocation sources.This study might be of significance to gaining a deeper understanding of the brittle-to-ductile transition of materials.     

四参数全范围da/dN曲线测定方法研究

机械结构设计的损伤容限分析,需要使用材料疲劳裂纹扩展速率曲线性能。在总结传统疲劳裂纹扩展曲线的基础上,本文讨论了四参数全范围da/dN曲线公式;基于断裂力学原理,分别给出了此公式中材料裂纹扩展门槛值ΔKth,断裂韧性K1C和张开函数f的测定方法;利用多元线性回归法对试验数据进行了曲线拟合,得到了四参数全范围da/dN曲线公式的参数估计式;将此公式运用于不同应力比下的裂纹扩展速率试验数据拟合,通过试验数据的拟合结果可以看出:四参数全范围da/dN曲线公式,能够充分有效合理地表征全范围裂纹扩展速率的物理特性和宏观数据规律,且参数估计简便,拟合精度高;从而验证了四参数全范围da/dN曲线公式的有效性和合理性,并将得到广泛应用。     

直立顺层边坡的黏弹性稳定分析

直立边坡的失稳与岩体的流变性质密切相关，其在一定载荷作用下失稳表现出延迟特性。采用自重作用下的梁柱力学模型，考虑岩石的流变性，给出了不同材料模型下直立边坡的极限坡高及其分析方法。     

V型缺口裂端的三维应力状态及约束分析

利用三维有限元方法，研究了有限厚度板中V型缺口根部穿透裂纹前沿的三维弹性应力场。对不同厚度、不同缺口张开角和裂纹长度对应力强度因子及裂尖附近的三维约束程度的影响进行了分析，同时还讨论了三维约束区的大小。研究结果显示：当缺口张开角小于60度时，不同缺口的应力强度因子和离面约束因子的分布基本一致，角度的影响不明显。应力强度因子是厚度的函数，板中面的应力强度因子随厚度的增加逐渐减小趋近干平面值，最大为1．08倍的平面值。当板厚超过15倍的缺口深度时，应力强度因子最大值将从中面转移至接近自由表面位置，距中面约0．4倍板厚。三维约束非常明显的区域在裂尖前沿约0.45倍厚度的范围内．二维到三维的过渡区在裂尖前沿1.5倍厚度的区域内；在中面上三维效应影响区最大，随着离中面距离的增加逐渐减小，在自由表面上降为0。     

A DECAGONAL QUASICRYSTAL WITH AN ARC-SHAPED CRACK

A decagonal quasicrystal,which is weakened by an arc-shaped crack penetratingthrough the solid in the period direction,and which is subjected to remote uniform phonon stresses,is investigated by applying the complex variable method which is just developed by the authors.It is found that the phonon and phason stresses near the crack tips exhibit inverse square rootsingularities.The four complex stress functions characterizing the phonon and phason fields arederived.Explicit expressions for the phonon and phason stress intensity factors,crack openingdisplacements and energy release rate are also presented.     

Three-Dimensional Dynamic Contact Problem for an Elliptic Crack Interacting with a Normally Incident Harmonic Compression–Expansion Wave

The paper deals with the three-dimensional dynamic problem for an elliptic crack interacting with a normally incident harmonic compression–expansion wave, considering the contact interaction of the crack faces. An asymmetric solution is obtained using an iteration algorithm developed earlier. Numerical results are presented     

Creeping flow of viscoplastic materials through a planar expansion followed by a contraction

In this work, the creeping flow of a viscoplastic fluid through a planar channel with an expansion followed by a contraction is analyzed numerically. The solution of the conservation equations of mass and momentum is obtained via the finite volume method. In order to model the non-Newtonian behavior of the fluid, it was used the generalized Newtonian fluid constitutive equation. The viscosity function was the one proposed by Souza Mendes and Dutra [Souza Mendes, P.R., Dutra, E.S.S., 2004. Viscosity function for yield-stress liquids. Appl. Rheol. 14, 296–302]. The yielded and unyielded regions are obtained for several combinations of rheological parameters. The influence of these parameters on pressure drop through the cavity is also obtained and analyzed.     

裂尖超钝化:实验、理论与数值模拟

本文报道了在改性聚丙烯裂尖平面应变段发生超钝化的实验发现。利用环向冷拉模型,可说明裂尖超钝化的形成取决于冷拉传播速率与加载率之比。裂尖超钝化可使材料韧性,尤其是冲击韧性的改善,达到一个新的水平。本文在超弹性-粘塑性各向异性损伤的有限变形本构模型下进行了详尽的数值计算。模拟结果成功地再现了裂尖超钝化的基本特征。     

复合型表面裂纹疲劳门槛应力的估算

表面裂纹是工程构件常见的缺陷，由于实验数据的缺乏及其他困难，断裂力学应用于表面裂纹的疲劳扩展，其经验和成果还十分有限。本文利用复合型断裂准则，对圆棒试样表面小裂纹的门槛应力进行分析和估算，得到了较满意的结果。     

试验确定自增强圆筒的表面裂纹K1因子和疲劳扩展规律

本文提供了一种可以进行自增强处理的圆筒试样,通过实验用柔度法确定了该试样的表面裂纹的应力强度因子,介绍了含表面裂纹试样的柔度测试技术,导出了柔度与表面裂纹尖端前缘各点的应力强度因子的关系式,该式可作为各种含表面裂纹试样柔度法测表面裂纹 K_1因子的参考,本文还测定了不同自增强程度下,自增强圆筒的表面裂纹疲劳扩展规律。