焦散线法确定应力强度因子的条件

基于焦散线的形成原理及含裂纹受力试件在裂尖附近区域的应力分布，得到了焦散线法确定应力强度因子的条件：初始曲线半径与试件厚度之比大于0．5。当满足该条件时，对光学各向同性材料及光学各向异性材料前表面反射的情形，只需测量焦散线沿横向的最大尺寸便可较精确地确定应力强度因子；而对于光学各向异性材料的透射或后表面反射情形，只有在忽略远场非奇异应力的影响后，才可借助焦散线的横向尺寸近似确定应力强度因子。

Condition of Caustic Method for Stress Intensity Factor Determination

Based on the caustic formation principle and stress distribution near crack tip of loaded specimen, the condition of caustic method for stress intesity factor determination was obtained. The condition is that the proportion of initial curve radius to specimen thickness is larger than 0.5. When the condition is satisfied, the stress intensity factor can be determined by caustic transvers dimension for optically iso-tropic material, as for birefringent material. If the case of front surface reflection is concerned, there is the same conclusion as above. If the case of rear surface reflection or penetration is concerned, the effect of far field nonsingular stress being neglected, the stress intensity factor can be approximately determined by caustic transvers dimension.