用变裂缝单一尺寸试样确定大理岩的断裂韧度

采用具有不同长度裂缝单一尺寸的中心圆孔平台圆盘试件,测定了大理岩的断裂韧度。基于Bazant的尺度律理论,根据有限元分析的结果拟合得到了无量纲能量释放率g(α0)的函数表达式,当无量纲裂缝长度α0=a0/R在0.28~0.51的范围时,与试件形状有关的函数g′(α0)/g(α0)的变化范围为1.0～5.8,能够满足Bazant尺度律公式中对脆性数β范围的需求。由试验结果得到了与试件尺寸无关的断裂韧度的真实值KImc和断裂过程区长度cf。用该方法确定岩石的断裂韧度,能够避免使用较大尺寸的试件,以及为得到足够大的β值范围而使用两种或两种以上试件的准备和试验带来的困难。

DETERMINATION OF MARBLE FRACTURE TOUGHNESS BY USING VARIABLE-CRACK ONE-SIZE SPECIMENS

One-size flattened disc specimens with identical centre hole and different initial crack lengths are used to determine marble fracture toughness. Based on the size effect law proposed by Bazant, the dimensionless energy release rate function g(α0) is curve fitted with the data from the finite element analysis. It is concluded that the range requirement for the brittleness numbers β in the size effect law is satisfied, if the function g′(α0)/g(α0), which is related to the specimen shape, varies from 1.0 to 5.8, this condition is equivalent to that the dimensionless initial crack length α0=a0/R varies from 0.28 to 0.51. According to the analysis of experimental results, the real fracture toughness K Imc which is independent of specimen size and the length of fracture process zone cf are given. The present method of determination of rock fracture toughness avoids the difficulties in specimen preparation and testing, and there is no need to use larger specimens or two or more than two types of specimens for getting a sufficient range of brittleness numbers β.