The Indentation Test of Three Kinds of Sandstone Material Based on DIC and AE Technology

The circular blade has become the dominant edge type for tunnel boring machine disc cutters because of its outstanding wear resistance compared to wedge-shaped blades. To investigate the fracture process and damage pattern of rocks under the indentation of circular punches, indentation experiments were carried out on three sandstones using the digital image correlation (DIC) and acoustic emission (AE) simultaneous test system. A penetration force prediction model considering the radius of the indenter and the penetration depth was established based on contact mechanics. The stress distribution in the rock was determined under a circular indenter. The strain characteristics of the indentation test of three types of sandstone captured by DIC technology verified the model results. The experimental results showed the following: (1) The established mechanical model effectively describes the relationship between the penetration force and depth, and the analytical solution of the model agrees with experimental data. (2) The stress distribution of the rock in the theoretical model is consistent with the rock strain measurements in the experiments. The plastic area increases with penetration depth, but the rate of increase gradually decreases. After reaching the peak point of specimen fracture, the range no longer increases when the loading continues. (3) With penetration depth increase, the range of AE hits and parameters change in stages. After the overall fracturing of the sample, AE hits still occur, but the range does not significantly increase.