EFFECT OF A MICRODEFECT AHEAD OF A MAIN CRACK ON STRENGTH OF SOLIDS -(EXACT SOLUTION TO THE MAIN CRACK MICRODEFECT INTERACTION-MODEL)

In our previous paper, an approximate solution to the main crack-micro defect interaction model was derived using a main crack stress field, and the effect of a microdefect ahead of a main crack on the strength of solids was discussed in terms of the model. In the present paper, i n order to investigate more precisely the above effect, the main crack -microdefect interaction model is formulated more specifically based o n the method of continuously distributed theory of dislocations, and t he distribution functions for both a main crack and a microdefect are obtained. As a result, we obtain stress intensity factors K both at th e tip of a main crack and a microdefect in the closed form. Using thes e K values, we elucidate the effective range of the above model and th e crack shielding effect by a microdefect. Furthermore, the crack leng th dependence of the fracture strength and fracture toughness of engin eering ceramics can be explained well theoretically using the present model.