Experimental and numerical investigations on fracture behaviours of cracked chevron notched Brazilian disc (CCNBD) sandstone specimen under cyclic loading

Abstract

In this work, laboratory tests and numerical simulations were used to investigate the fracture behaviour of Cracked Chevron Notched Brazilian Disc (CCNBD) sandstone specimens subjected to cyclic loading. A series of fracture tests performed on CCNBD specimens, including static loading and cyclic loading. The cycle upper limit load was set as 0.75SUL (static ultimate load), 0.85SUL, and 0.95SUL, respectively. The fracture surface topography was also reconstructed by a 3D laser scanner to analyse the fracture characteristics. The results show that the phenomenon of ‘stress lags behind strain’ and ‘strain lags behind stress’ can reflect the evolution of hysteretic rings under cyclic loading, and the spacing between hysteretic rings increases with the increase in upper limit load. A weakening effect of the cyclic loading on the mode I fracture toughness can be found, and the more cycles there are, the smaller is the fracture toughness. The threshold value of the upper limit load is approximately 0.75SUL − 0.80SUL in this work. The nonlinear development of the fracture process zone can be divided into three stages: the initial stage, stable stage, and acceleration stage. In addition, a higher fractal dimension reflects an uneven and rougher fracture surface, and the more cycles there are, the rougher is the fracture surface topography. Based on the proposed meso-dilatancy model, the failure reason is confirmed as the larger tangential deformation caused by cyclic loading, and a larger tangential deformation leads to a rougher fracture surface.