Abstract
Abstract The thesis focus on the mixed-mode Ⅰ/Ⅱ crack which is very common in fracture problem. Study the stress and strain around crack tip by micro mechanics method and exploit the fracture criterion to predict the fracture toughness of pure modeⅠ, pure modeⅡ and mixed-mode Ⅰ/Ⅱ.Two fracture criterion, maximum principle stress theory（MPST） and maximum distortion energy theory（MDET）, are used in this thesis. The fracture toughness of mixed-mode Ⅰ/Ⅱ by MDET is similar to the result of experiment.When using both fracture criterions to predict the fracture toughness of pure modeⅠ,the smaller radius the crack is,the the smaller fracture toughness of pure modeⅠ is. It isn＇t related to the fracture criterions we use.We compare the crack growth angle of pure modeⅡ we predict to the experiment result, and discover that the result don＇t match. The possible reasons are：（1）The experiment equip couldn＇t perfectly simulate the condition of pure modeⅡ.（2）The fracture criterions we use are merely focus on certain point＇s stress or strain, but the crack growth angle of material isn＇tII only related to the certain point but also related to the proximity of the certain point.So it＇s possible that crack growth don＇t occur on the point of maximum stress or strain.