The digital-laser dynamic caustics system in combination with a static-dynamic loading device was utilized in the blasting fracturing test,in which the PMMA specimens underwent four kinds of vertical static stresses (0,3,6 and 9 MPa,respectively) with the strictly same total charge.By using the fracture mechanics theory,the mechanism of the fracture and propagation behaviors of the cracks along the static principle stresses was analyzed.The result indicates that the stress concentration is first created under the pre-applied vertical stress field around the borehole,where the maximum tensile stress is located on the borehole wall corresponding to the far-field maximum principle stress direction.Then,when disturbed by the dynamic loads induced by blasting,the crack is precociously initiated from the maximum tensile stress point and extends along the maximum principle stress direction.Furthermore,the crack velocity increases accordingly with higher vertical pre-static stresses;the greater the crack velocity increases,the higher the stress intensity factor of the crack tip.%采用动静组合加载实验装置和数字激光焦散线实验系统,进行了0、3、6、9 MPa等4种压应力场中PMMA试件的爆破致裂实验,分析了沿静态主应力方向扩展的裂纹运动学和力学行为.实验结果表明:首先,静态竖向载荷在预制炮孔周围产生应力集中,在炮孔壁上下端部处出现最大拉应力;随后,在动态爆炸载荷的叠加作用下,裂纹优先在炮孔壁上最大拉应力位置处起裂,并沿最大主应力方向扩展;裂纹扩展过程中,静态竖向载荷越大,裂纹扩展速度越大,且裂纹尖端应力强度因子值越大.
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