空孔与运动裂纹相互作用的动焦散线实验研究

为研究预制裂纹不同偏移距离时运动裂纹与空孔的相互作用规律，采用动态焦散线实验系统，将预制裂纹的偏移距离设定为唯一变量，对含空孔的有机玻璃(PMMA)试件进行冲击三点弯实验。研究表明，存在两个临界距离:（6 mm (2 R )、9 mm (3 R )），在该偏移距离下，裂纹扩展轨迹、动态断裂特性发生显著改变:(1) 预制裂纹偏移距离不大于3 mm时，裂纹贯穿空孔，发生二次起裂，且二次起裂的速度与应力强度因子显著大于一次起裂，无偏移时裂纹轨迹的分形维数为最小值；(2) 偏移距离增大至6 mm时，裂纹不再贯穿空孔，空孔对裂纹先吸引后排斥，裂纹速度与应力强度因子先减小后增大，裂纹轨迹的分形维数达到最大值；(3) 偏移距离大于6 mm时，空孔对裂纹的吸引作用逐渐减小，大于9 mm后，空孔对裂纹的吸引不再显著，裂纹起裂后即向落锤加载方向扩展直至贯穿试件。

Experimental study on dynamic caustics of interaction between void and running crack

In order to study the interaction between running cracks and voids in the offset distance of different prefabricated cracks, setting the offset distance of the pre-crack as the unique variables, do impact three-point bending test on PMMA specimens with voids based on dynamic caustics experiment system. Researches show that: There are two critical distances, 6 mm (2R), 9 mm (3R). At these distances, the extended trajectory and dynamic fracture characteristics of the crack change significantly. (1) When the pre-crack offset distance is no greater than 3 mm, the specimen cracks for the second time. The rate and stress intensity factor of the second crack initiation are significantly greater than the first. The fractal dimension of the crack trajectory is the minimum when the pre-crack does not offset. (2) When the offset distance is increased to 6 mm, the void is attracted to the crack and then repelled, but the crack never penetrates the void. Crack velocity and stress intensity factor decrease firstly and then increase. The fractal dimension of the crack trajectory is up to the maximum. (3)When the offset distance is greater than 6 mm, the attraction of voids to cracks is gradually reduced. When the offset distance is greater than 9 mm, the attraction of void to cracks is no longer significant. Crack expands to the falling hammer after crack initiation and finally penetrates the test piece.