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关于动态断裂的全过程,包括动态起裂、扩展和止裂的报道在科学文献中受到日益增长的关注。研究岩石的动态扩展和动态止裂,用分离式霍普金森压杆径向冲击大直径(φ160 mm)的预裂人字形切槽巴西圆盘(pre-cracked chevron notched Brazilian disc——P-CCNBD)试样的试验,测定了大理岩的I型动态扩展韧度,而不仅是动态起裂韧度。确定的方法是试验―数值―解析法,而不是通常的准静态法,因为,大尺寸试样在动态试验中不满足应力平衡条件。裂尖起裂时刻和裂纹扩展速度采用应变片和裂纹扩展计监测;将有关试验数据,包括霍普金森压杆施加在试样上的的动态荷载输入有限元程序,对P-CCNBD进行三维动态数值模拟,再结合普适函数的半解析修正,得到动态应力强度因子的时间历程。结果表明,P-CCNBD大理岩试样的动态起裂韧度随加载率的增大而增大,试样的动态扩展韧度略低于动态起裂韧度,且扩展韧度随裂纹扩展速度的加快而增大。此外,对裂纹扩展速度振荡和扩展路径曲折现象进行了分析,讨论了P-CCNBD试样实现动态止裂的可能性。
With regard to the whole process of dynamic fracture, reports including dynamic fracture initiation, propagation and crack arrest are receiving more and more attention in the scientific literature. The dynamic expansion of the rock and the dynamic arrest of the rock were studied by using a split Hopkinson pressure bar to impact the large diameter (φ160 mm) pre-cracked chevron notched Brazilian disc - P-CCNBD ) Test of the specimen, the type I dynamic expansion toughness of the marble was determined, not only the dynamic initiation fracture toughness. The method of determination is test-numerical-analytical, rather than the usual quasi-static method because large-size specimens do not satisfy the stress equilibrium conditions in dynamic tests. Crack tip crack initiation time and crack propagation rate are monitored by strain gages and crack dilatometer. The relevant experimental data, including dynamic load applied by Hopkinson pressure bar on the sample, are input to the finite element program to perform three-dimensional dynamic analysis of P-CCNBD Numerical simulation, combined with the semi-analytical correction of universal function, get the time history of dynamic stress intensity factor. The results show that the dynamic fracture toughness of P-CCNBD marble sample increases with the increase of loading rate, the dynamic expansion toughness of the sample is slightly lower than the dynamic fracture toughness, and the extension toughness increases with the crack growth rate Accelerated and increased. In addition, the phenomena of crack propagation velocity oscillation and extended path tortuosity were analyzed, and the possibility of dynamic crack arrest of P-CCNBD specimens was discussed.