层理方向对含预制裂纹页岩Ⅰ型断裂特性的影响

Effect of bedding direction on modeⅠfracture characteristics of precrack shale

层状页岩受内部层理方位分布特征的影响,其力学性质常表现出明显的各向异性特征。为了探究层理方向对层状页岩Ⅰ型断裂特性的影响,针对不同层理倾角β、预制裂纹角度为0°的半圆盘试件开展三点弯曲静态压缩试验和数值模拟试验。试验结果表明,试件的Ⅰ型标准化应力强度因子YⅠ会随着层理倾角的变化呈现出明显的差异性,并与层理倾角呈现出良好的三次函数关系,且仅在层理倾角β为0°和90°时,试件表现为纯Ⅰ型断裂模式,即层理倾角的变化会改变试件的断裂模式。同时,试件的Ⅰ型断裂韧度随着层理倾角的增大而逐渐减小,并与层理倾角呈二次函数关系;当层理倾角与预制裂纹角度垂直时,试件的Ⅰ型断裂韧度最大;而当层理倾角和预制裂纹角度平行时,试件的Ⅰ型断裂韧度最小。另外,基于扩展有限元法(XFEM),对半圆盘层状页岩试件的破断机制进行研究,验证了试验和计算结果的准确性。

The mechanical properties of layered shales are usually anisotropic due to the influence of internal bedding azimuths.In order to explore the influence of bedding direction modeⅠfracture characteristics,three point bending static compression tests and numerical simulation tests were carried out on half-disc specimens with precrack angles of 0°and different bedding dip angleβ.The test results show that the modeⅠstandardized stress intensity factor of the specimen YⅠvaries significantly with the change of bedding angle,and presents a good cubic function relationship with bedding angle;only when the bedding angleβis 0°or 90°,the specimen shows a pure modeⅠfracture mode,that is,the change of bedding angle will change the fracture mode of the specimen.At the same time,the modeⅠfracture toughness of specimens decreases gradually with the increase of bedding angle,and presents a quadratic function relationship with bedding angle.When the bedding angle is perpendicular to the precrack angle,the modeⅠfracture toughness of the specimen is the largest.When the bedding angle is parallel to the precrack angle,the modeⅠfracture toughness of the specimen is the smallest.In addition,based on the extended finite element method(XFEM),the fracture mechanism of the half-disc layered shale specimen is studied,and the accuracy of the test and calculation results is verified.