V形切槽巴西圆盘法测定岩石断裂韧度K_(IC)的实验研究

采用国际岩石力学学会岩石断裂韧度建议测试方法(ISRM)1]提出的V形切槽巴西圆盘试样(CCNBD),测试了一种泥质砂岩的I型断裂韧度值,给出了一套试样切割制备方案,从试验现象角度分析了该泥质砂岩的断裂力学特性,讨论了该试样类型的有效尺寸和断裂机制,并指出了该方法的特点和优劣性,得出如下结论:(1)该类岩石试样测得的I型断裂韧度值对CCNBD试样直径尺寸变化具有较大的敏感性,并且直径大于ISRM建议方法中最小有效直径(75mm)的试样测试结果更为稳定;(2)CCNBD试样断裂机制表现为以拉张应力(间接拉伸)作用为主,兼有一定的韧带面内剪切作用的应力状态下I型裂纹扩展模式;(3)V形切槽巴西圆盘方法具有试样加工工艺简单、能承受较大临界载荷、测试的I型断裂韧度值较稳定等优点,但其没有考虑断裂过程区(FPZ)的非线性问题,建议对该方法进行非线性修正图解方案研究,以达到更准确测定岩石断裂韧度的目的。

Research for determining mode I rock fracture toughness KIC using cracked chevron notched brazilian disc specimen

Cracked chevron notched brazilian disc (CCNBD) specimen configuration has been used to test the mode I fracture toughness of muddy sandstone according to the ISRM d suggested testing method in 1995. A new cutting procedure of CCNBD specimen is given. Specific rock fracture characteristics have been observed. The valid size range and fracture mechanism of this specimen type have been discussed. Then the advantages and disadvantages of CCNBD method are pointed out. It can be concluded as follows: (1) Derived fracture toughness values are sensitive to the variation of CCNBD specimen diameters; and more consistent fracture toughness values can be derived by the specimen with larger diameter than the ISRM suggested “minimum effective diameter 75 mm”. (2) Fracture mechanism of CCNBD specimen is mode I crack growth type under the synthetic stresses of the dominant tensile stress (indirect tensile) and the in-ligament shear stress. (3) CCNBD method has advantages with simple sample preparation, bearing a greater critical load and generating compatible KIC values. But this method has not considered the nonlinearity of fracture process zone (FPZ); and it is lack of the nonlinearity calibration procedure. It is advised to develop nonlinearity calibration procedure for the CCNBD method in order to generate more accurate testing results.