Impact Test and Crack Propagation Law of Rock-like Materials with Different Joint Geometric Parameters

The crack-propagation behavior and dynamic response characteristics of artificial jointed rock-like materials under impact loading were investigated. Drop-weight impact tests were conducted using a self-developed apparatus, in which joint aperture, inclination angle, number of joints, and the distance between the joint and the loading surface were taken as geometric parameters. LS-DYNA was used to establish numerical models of drop-weight impact for vertical combined joints composed of multiple parallel vertical joints and for vertical-horizontal combined joints consisting of one set of vertical joints intersecting with one set of horizontal joints. The influence of joint geometric parameters on the failure mode, crack-propagation path, and stress-strain response of the jointed rock-like materials was analyzed. Based on the linear elastic fracture mechanics theory under the plane stress assumption, the relationship between the strain components at the joint end and the stress intensity factors was derived. The test results show that as the joint aperture increased from 0.5mm to 0.9mm, the maximum impact load decreased from 35.16kN to 22.07kN; as the joint inclination angle increased from 30° to 60°, the maximum impact load decreased from 47.17kN to 29.57kN; and as the number of joints increased from one to three, the maximum impact load decreased from 36.31kN to 23.69kN, all showing a decreasing trend. When the distance between the joint and the loading surface increased from 50mm to 90mm, the maximum impact load first increased from 38.19kN to 41.75kN and then decreased to 40.88kN, showing a nonlinear increase-decrease relationship. The peak strain at the measurement points was negatively correlated with the joint aperture, inclination angle, number of joints, and joint-loading surface distance. The numerical simulation results indicate that the overall stability of the model decreases significantly with an increasing number of vertical joints; in the vertical-horizontal combined joint model, enlarging the vertical joint aperture reduces the degree of bottom damage, and when the horizontal joint is located above the vertical joint, the model becomes more susceptible to instability and failure.