Experimental investigation on internal offset crack of PMMA beam using caustics

In this paper, the dynamic stress intensity factor (DSIF) at the crack tip of a PMMA beam containing an internal offset crack under impact loading was investigated by using a transmission digital caustic test system combined with high-speed camera. Firstly, the stress intensity factor, as well as velocity, of the mixed-mode crack tip under static and dynamic loading were derived based on the transmission caustic method; secondly, a drop hammer loading test was conducted on the different specimens with biased cracks in the beam using the transmission caustic test system to obtain the dynamic fracture mechanics parameters of internal crack initiation and expansion; then, the crack initiation angle and expansion path analysis of the impact-generated expansion cracks were performed based on the theoretical analysis and the differences between the fracture process and that of the specimens containing internal symmetric cracks were discussed. The results show that the different locations of the internal off-set cracks make the stress redistribution process inside the beam and the stress state at the crack tip during the crack extension process different, and the fracture process and fracture mechanics parameters are different from those of the specimens with internal symmetric cracks, the results of the caustic test are in good agreement with the numerical analysis. The research results can provide guidance for the study of the fracture process of brittle materials such as PMMA containing internal defects.