线弹性断裂力学基础.pptx

线弹性断裂力学基础;引言;3;第一节断裂模式与裂纹类型;断裂模式;剪切断裂;通常用所处理问题的维数来说明裂纹在空间的构型，如平面内的裂纹叫做二维裂纹，空间内的裂纹叫三维裂纹等等。;裂纹类型;裂纹类型;穿透裂纹;第二节裂纹尖端附近的应力场和位移场;;;II 型断裂;;II 型断裂;;第三节应力强度因子(Stress Intensity Factor-SIF);1. 问题;应力集中与应力奇异;应力强度因子;? ? ;解析方法(闭合解);LEFM中应力强度因子可叠加;应力强度因子举例-线状裂纹;应力强度因子举例-线状裂纹;应力强度因子举例-线状裂纹;圆柱壳 ;式中，f(a,W,...)称为几何修正系数，反映构件和裂纹几何尺寸对裂尖应力场的影响。;Newman-Raju解;应力强度因子举例-面状裂纹;第四节材料的断裂韧度(Fracture Toughness);断裂韧性;试验标准;试样;先在试件的相应位置用线切割机床切一切口，线切割使用的钼丝直径约0.1mm,左右，太粗的切口将不利于裂纹的预制。切口的尺寸应小于预定裂纹尺寸，以留有用疲劳预制裂纹的余地。;试验装置;PQ是裂纹开始扩展时的载荷;工具显微镜;PQ;[解答] ;[解答] ;[解答] ;常用金属材料KIC数据;常用金属材料KIC数据;常用金属材料KIC数据;平面应力断裂韧性;第五节断裂判据与断裂控制设计的基本思路;在线弹性条件下，低应力脆性断裂的判据为;;工作应力 ;52;53;54;55;56;57;58;59;第六节应变能释放率(Strain Energy Release Rate);Griffith 能量平衡;Griffith 能量平衡;应变能释放率;Father of Modern Fracture Mechanics;应变能释放率;应变能释放率;应变能释放率与应力强度因子的关系 ;应变能释放率与柔度;应变能释放率与柔度;应变能释放率与柔度;应变能释放率与柔度;应变能释放率与柔度;应变能释放率与柔度;应变能释放率与柔度;应变能释放率与柔度;第七节复合型断裂问题(Mixed-Mode Fracture);Practical structures are not only subjected to tension but they also experience shear and torsional loading. Cracks may therefore be exposed to tension and shear, which leads to mixed mode cracking. The combination of tension and shear gives a mixture of modes I and II. Several investigators have considered the mixed mode fracture problem, but a generally accepted analysis has not yet been developed. The discussion here will be limited to the I—II mixed mode. ;Mode II loading under an in-plane shear stress ? can be characterized by a stress intensity factor, ;When using an energy balance criterion the total energy release rate GT, is given by: ;For I-II mixed mode loading, ;;The fracture condition is more likely to be: ;;起裂的断裂判据;The previous criterion is based on the assumption that the crack propagates in a self-similar manner. In other words, it is assumed that crack extension will be in the plane of the original crack. This is necessarily so, because the expressions for G and their relations to K were derived on this premise. In mixed mode experiments, it is usually o