Suggested Methods for Determining Dynamic Fracture Toughness and Numerical Investigation of Cracking Processes under Impacting Loads

Abstract

Initiation toughness, propagation toughness, and arrest toughness can be considered as threshold values to predict the dynamic behavior of cracks in initiation, propagation, and arrest. For rock materials, initiation toughness has been studied extensively, whereas propagation toughness and arrest toughness have received less attention. In this study, a single cleavage semicircle compression (SCSC) specimen was proposed, and Ya’meng black sandstone was selected to make the SCSC specimens. Impact tests were conducted using the SCSC specimens and a split Hopkinson pressure bar (SHPB) test system. Crack initiation time, propagation time, and propagation speed were measured using crack propagation gauges (CPGs). A high-speed photography (HSP) system was also used to observe the dynamic behavior of crack propagations and arrests. Dynamic stress intensity factors (SIFs) were calculated using ANSYS code, and the crack propagation path was simulated using AUTODYN code. The simulation results generally agree with the test results. Dynamic initiation toughness, propagation toughness, and arrest toughness were determined using an experimental–numerical method. The results show that crack propagation speeds vary during crack propagations, and cracks may arrest for one or more periods during propagation. Dynamic initiation toughness is proportional to the loading rate applied to the specimens, and arrest toughness is less than both initiation toughness and the propagation toughness for the Ya’meng sandstone.