砂岩Ⅰ型断裂的尺寸效应试验研究

通过对尺寸成等比例的砂岩试样进行三点弯曲试验,研究了 Ⅰ 型断裂问题中试样尺寸对砂岩断裂参数的影响.结果表明:随着试样尺寸的增大,名义张拉强度减小,名义断裂韧度和破裂过程区长度增大,三者均为试样尺寸的函数.基于试验结果,引入有效破裂过程区长度cf,建立等效线弹性断裂力学尺寸效应模型,通过理论分析,发现其尺寸效应曲线介于理想脆性和理想塑性材料之间,体现出准脆性材料的尺寸效应特点,并计算得到了不同尺寸试样的破裂过程区长度等断裂参数.为验证该尺寸效应模型在砂岩中的正确性,采用数字图像匹配技术(DIC)测定相应尺寸砂岩试样的破裂过程区长度,测定结果和理论模型计算值相符.

Experimental investigation for effect of size on sandstone Mode Ⅰ fracture

To study the effect of specimen size on fracture parameters in Mode Ⅰ fracture issue, a group of geometrically similar sandstone specimens were tested by three-point bending. The result shows that as the size of specimen increases, apparent tensile strength decreases and the apparent fracture toughness and length of the process zone increase. These three factors are a function of size. Based on these test results, equivalent linear elastic fracture mechanics (ELEFM) was used to calculate fracture parameters such as the length of the process zone in rock material. The fracture mechanism of sandstone was identified to be between the perfectly plas-tic and perfectly brittle limits and the effect of size on quasi-brittle material was shown. To verify the correctness of ELEFM, the length of the process zone was obtained by digital image correlation (DIC) test and the experimental and theoretical results were found to fit well.