【作者】 丘波；

【导师】 钱才富；

【作者基本信息】 北京化工大学 ， 化工过程机械， 2005， 硕士

【摘要】 本论文的研究是国家自然科学基金项目“纳米裂纹形核的力学模拟和实验研究”的一部分,目的在于探讨裂纹形核和扩展机理。论文分TEM实验观察与计算机数值模拟两部分。 通过对奥氏体不锈钢材料的TEM原位拉伸实验,发现材料本身存在着很多诸如裂纹与位错等形式的缺陷,在外加载荷的作用下,位错从裂纹尖端会如水波状从裂纹尖端,沿各个方向扩散出来,达到平衡后,在裂前端存在一无位错区(DFZ),位错群在无位错区(DFZ)的外边缘积塞;若继续加载,在无位错区中可能出现原子键断裂而产生微裂纹,它与主裂纹都将继续扩展,并最终汇合在一起,形成更大的裂纹。若发射出来的位错群前方有障碍,如晶界等,从裂纹尖端发射出来的错群,将在障碍前积塞。 利用位错与裂纹的相互作用模拟位错从裂纹的发射过程发现:Ⅱ型裂纹塑性区由三部分组成,最大的部分位于裂纹前方,这与按von Mises屈服准则求得的哑铃状塑性区形状有所不同;Ⅰ型裂纹塑性区是由关于裂纹面对称的上下两瓣组成,该形状与按von Mises屈服准得到的塑性区形状相似;裂纹有效应力强度因子随位错发射数量的增加而减少,而残余的应力强度因子在位错发射结束后也与外加的应力强度因子无关;在同样大小的外加应力强度因子作用下,Ⅱ型裂纹无位错区和塑性区比Ⅰ型裂纹大得多;Ⅰ+Ⅱ复合型裂纹中塑性区和无位错区不更多还原

【Abstract】 This work is part of the project of "mechanical simulation and experimental investigation of the nucleation of nano-cracks" supported by the National Natural Science Foundation of China (Grant No. 10272020). The purpose is to investigate the mechanisms of crack initiation and propagation. This thesis is concentrated on TEM observation and computer simulation of dislocation emission from a crack.TEM observation of dislocation emission was carried out on an austenitic stainless steel. It is found that defects such as cracks and dislocations exist in the materials. Upon loading, dislocations were emitted out from crack tips along multiple directions. When the dislocation emission process stopped there exists a dislocation-free zone in front of the crack tip, and the emitted dislocations are inversely piled-up outside the dislocation-free zone. Increasing the applied load, micro-cracks may initiate inside the dislocation-free zone as a result of breakdown of atomic bonds and crack propagation is achieved by coalescence of the micro-cracks and the main crack. The emitted dislocations may pile-up at更多还原