Experimental study on coal impact fracturing based on temporal and spatial evolution of deformation field

The evolution characteristics of deformation fields and displace fields of the deformation localization are in- vestigated and analyzed by using the digital speckle correlation method. The test material is a kind of coal and the specimens are loaded by Hopkinson bar impact loading device. Experimental data are collected with high-speed camera. The analysis results show that:① The initial deformation field is relatively uniform,and the characteristic of deformation localization is obvious with the increase of load. The temporal and spatial evolution of the deformation field is characterized as two stages:before the stress peak,the horizontal deformation value develops rapidly and the vertical deformation value develops slowly;due to the evolution of fracture,after the stress peak,the horizontal deformation val- ue develops slowly and the vertical deformation value develops rapidly. ② In the loading process of Hopkinson bar,at both ends of the test piece,the local crushing zone appears. During the loading process,the main crack is initiated from the crushed zone and extended to the other end through the radial loading direction. ③ The experimental results show that the stress of coal sample under the impact load increases linearly with the strain. Compared with static load,the e- lastic modulus is greatly improved. Due to the presence of the crushed zone,the strength of coal samples with impact loading test is relatively small compared with the actual results.