有限宽切槽对CCNBD断裂试样应力强度因子的影响

Effects of finite notch width on stress intensity factor for CCNBD specimen

国际岩石力学学会(ISRM)在1995年提出一种新型的岩石断裂韧度试样——人字形切槽巴西圆盘试样(cracked chevron notched Brazilian disc——CCNBD),对该试样的一个重要力学参数即最小无量纲应力强度因子的标定,以前的分析和计算都没有考虑切槽宽度的影响。然而试样切槽的宽度受切割刀具厚度所限,不能为零。当试样较小时,切槽宽度则相对较大。通过三维边界元计算分析表明,切槽宽度越大,无量纲应力强度因子的标定值就越大;对于ISRM推荐的CCNBD标准试样,得出其最小无量纲因子值为0.954,这比ISRM给出对应值0.84要大13.6 %。同时,小裂纹应力强度因子曲线的变化趋势也发生了质的变化,这可能会导致实验的失败。推荐最小无量纲应力强度因子的标定采用考虑切槽的三维分析。

International Society for Rock Mechanics ( ISRM ) proposed in 1995 a new type of rock fracture toughness specimen棗cracked chevron notched Brazilian disk ( CCNBD ), the previous analytical and numerical studies of the dimensionless stress intensity factor, which is an important mechanicel parameter, does not take into account the effects of finite notch width. Since the minimum chevron notch width is limited by the size of the cutting wheels used to produce it and can not be zero, as the specimen size get small enough, the notch width would become large in relation to the sample size. Our 3D BEM(Boundary Element Method) calculation shows that the larger the notch width is, the bigger the error makes for the dimensionless stress intensity factor. To the standard CCNBD specimen suggested by ISRM, this paper determines the minimum dimensionless stress intensity factor to be 0.954 which is 13.6 % larger than the value 0.84 given by ISRM; and the tread of the curve is changed when the crack is short, this could make the failure of the experiment. We recommend that a full 3D numerical analysis taking into effect of the notch width to be done whenever determine the dimensionless stress intensity factor.