Investigation of the fracture modes of red sandstone using XFEM and acoustic emissions

Acoustic emissions (AE) and stress-strain curve analysis are accepted methods of analyzing crack propagation and monitoring various failure stages, including crack closure and the crack initiation level, during rock failure under brittle rock loading. This study designed a series of three-point bending tests and shear fracture tests to investigate the features of AE signals for different modes. The Extended Finite Element Method (XFEM) is also adopted to simulate these experiments processes. The obtained results indicate that the maximum load for the shear fracture mode is approximately three times larger than that for the tensile fracture mode and that the displacement in the shear fracture mode is also larger than that in the tensile fracture mode. AE signals had higher AF (average frequency) and lower Rise Angle (RA) (ratio of the rise time to the peak amplitude) values when tensile failure occurred, while they exhibited lower AF and higher RA values when shear failure occurred. Accumulative AE energy for the shear mode is significantly larger than that for type I tensile fracture. The influence of inhomogeneity is also evident, as signals acquired at different distances exhibit distinct characteristics. The results show that AE leads to the characterization of the dominant fracture mode using only two AE descriptors. Note that we also should reasonably arrange AE sensors to monitor large-scale projects in the field.