Study of rock dynamic fracture toughness and crack propagation parameters of four brittle materials under blasting

Abstract

The study on dynamic fracture toughness (DFT) is of considerable practical interest because it can be used to predict cracked rock structure stability under blasting. The measurement method of dynamic fracture toughness under blasting loads is less addressed until now. In order to study the measurement method of DFT and crack propagation behavior under blasting, a new configuration specimen, i.e. single internal cracked circular disc (SICCD) specimen was proposed in this paper. Four types of brittle materials, black sandstone, red sandstone, green sandstone and PMMA were selected to prepare the SICCD specimens. Crack propagation gauges (CPGs) were glued along crack propagation paths to measure crack initiation and propagation time and crack propagation speeds. An oscilloscope and an ultra-dynamic strain amplifier were employed in the blasting tests. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the ingredient and microstructure of the brittle materials respectively. Finite element code ABAQUS was applied in the calculation of dynamic stress intensity factors (DSIFs), and the curves of the DSIF versus time were obtained. By using these curves and the breaking time of CPG filaments, the critical DSIFs of mode I crack at initiation and propagation were obtained. The results show that the measurement method of the critical DSIF of brittle materials under blasting is feasible and applicable. During crack propagations, the crack propagation speed and dynamic energy release rate are not constant. Comparing the test results of these four brittle materials, the initiation toughness and crack propagation speed increase with the elastic modulus of the brittle material under same blasting conditions.