Experimental and theoretical analyses of three-dimensional surface crack propagation

Abstract

通过双轴压力作用下岩石三维表面裂纹断裂试验,利用数字散斑技术,观察裂纹的翼形扩展、反向扩展,得出对应的时间和荷载。试验发现,三维表面裂纹的翼形扩展一般都先于反向裂纹,反向裂纹最先在远离裂纹尖端区域出现,而后快速与原裂纹尖端汇合。通过有限元计算得到三维裂纹试件整体应力场和裂纹前缘各点应力强度因子。通过复合型断裂判据,对裂纹翼形扩展的三维形态进行分析,试验结果与最大周向拉应力σmax及最大周向拉应变εmax判据的理论预示结果吻合较好。对反向裂纹萌生区域进行强度破坏分析,反向裂纹的萌生与莫尔–库仑强度理论的预示结果基本相符。从试验及理论2个方面分析三维表面裂纹扩展直至破坏的全过程。 An experimental investigation on three-dimensional(3D) surface crack under biaxial compression is conducted to investigate the growth of wing crack and anti-wing crack.A digital speckle camera is used to record the growth process of cracks during loading process.The images captured from the digital speckle camera are used for digital speckle correlation analysis to study the strain field of 3D surface crack.From the experiments,it is observed that the anti-wing crack initiates away from the crack tip region and then propagates towards the crack tip.The stress and the stress intensity factors along crack front are analyzed by using the finite element method.3D wing crack growth pattern is revealed by the mixed-model fracture criteria.The theoretical analyses indicate that the wing crack propagation can be predicted by the maximal circumferential stress criterion and maximal circumferential strain criterion.The strength failure analysis is also conducted in the anti-wing crack area.The anti-wing initiation and propagation can be predicted by the Mohr-Coulomb strength theory.The whole fracture and failure process of the 3D surface crack is analyzed by both experiments and theories.