基于P-CCNBD试样的岩石动态断裂韧度测试方法

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。

Test method for determining rock dynamic fracture toughness using P-CCNBD specimens

Pre-cracked chevron notched Brazilian disc (P-CCNBD) is made by slightly cutting the notch tip of cracked chevron notched Brazilian disc (CCNBD) into a straight crack front. The P-CCNBD specimens of sandstone are diametrically impacted by the split Hopkinson pressure bar, the experimental recordings are then used in the succeeding numerical analysis to get the mode-I rock dynamic fracture toughness. In order to verify the reliability of the numerical simulation, the dynamic finite element analysis for a finite crack in an infinite plate subjected to impact tension at crack faces is simulated first; the results of the numerical simulation are highly consistent with those in the literature. The results of our experimental-numerical method are compared with those of quasi-static method proposed by others, certain difference is observed. On the other hand, results of P-CCNBD are in good agreement with those of the more mature specimen (cracked straight-through Brazilian disc-CSTBD), both are determined with the experimental-numerical method. The derived dynamic initiation fracture toughness increases with increasing loading rate, demonstrating the loading rate effect. The drawbacks of the quasi-static method to test the dynamic fracture toughness are analyzed. The result obtained by experimental-numerical method is more reasonable.