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预裂的人字形切槽巴西圆盘(Pre-cracked chevron notched Brazilian disc,简称P-CCNBD)是将人字形切槽巴西圆盘(cracked chevron notched Brazilian disc,简称CCNBD)的切槽尖端再稍加切削制成直裂纹前沿的试样。利用霍普金森压杆对P-CCNBD砂岩试样进行径向冲击,完成I型动态断裂试验后再做数值分析得到岩石的动态断裂韧度。为了验证数值模拟的可靠性,先进行了无限平面中一条有限尺寸裂纹表面受冲击拉伸作用的动态有限元分析,结果表明,数值模拟的结果与Shi得到的结果非常吻合。将试验-数值法和他人的准静态法分别确定的砂岩的动态起裂韧度进行对比,两种方法得到的结果有一定的差异。采用试验-数值法,将比较成熟的直裂纹巴西圆盘(cracked straight-through Brazilian disc,简称CSTBD)和P-CCNBD两种试样测得的结果进行对比,两者吻合较好。得到的动态起裂韧度都有随着加载率的增加而增大的加载率效应。分析了准静态法的缺陷,认为试验-数值法得到的结果更为合理。
The pre-cracked chevron notched Brazilian disc (P-CCNBD) is made by cutting the notched tip of a cracked chevron notched Brazilian disc (CCNBD) Cutting the straight crack front made of the sample. The radial impact of P-CCNBD sandstone sample was carried out by using Hopkinson pressure bar, and the dynamic fracture toughness of the rock was obtained by numerical analysis after the completion of Type I dynamic fracture test. In order to verify the reliability of the numerical simulation, a dynamic finite element analysis of a finite-size crack surface in an infinite plane subjected to impact-stretching was performed. The results show that the numerical simulation results are in good agreement with those obtained by Shi. Comparing the dynamic initiation fracture toughness of sandstone determined by experiment - numerical method with that of others’ quasi - static method respectively, the results obtained by the two methods have some differences. The experimental results - numerical method were used to compare the results of the two samples, cracked straight-through Brazilian disc (CSTBD) and P-CCNBD. The resulting dynamic initiation toughness has the effect of increasing the loading rate as the loading rate increases. The defects of quasi-static method are analyzed, and the result obtained by experiment-numerical method is more reasonable.