Visualization of crack-grain boundary interaction in transparent crystals

采用光弹性法和蚀刻坑技术研究了NaCl透明双晶中的裂纹扩展行为及其相关现象。裂纹扩展发生在{001}解理面上，裂纹扩展前和扩展过程中沿{011}滑移面形成了许多滑移带。裂纹尖端越靠近晶界，裂纹扩展速度越慢，裂纹扩展的阈值应力强度因子KIC^<**>增大。腐蚀坑观察表明，裂纹尖端附近的位错密度在边界附近增大。从位错对裂纹尖端屏蔽的角度讨论了晶界对裂纹扩展行为的影响。

Crack propagation behavior and its related phenomena in NaCl transparent bicrystals have been investigated by using photoelastic method and etch-pit technique. Crack extension took place on the {001} cleavage plane, and matny slip bands were formed along the {011} slip plane before and during the crack extension. When the crack tip came closer to the grain boundary, crack extension became slower and the threshold stress intensity factor for crack extension KIC^<**> increased. Etch pits observation indicated that the dislocation density around the crack tip became higher near the boundary. The effect of grain boundary on such behavior of crack extension is discussed from the viewpoint of crack tip shielding due to dislocations.