Study on dynamic fracture behaviors of NSCB specimen under impact loading

The new experimental system of digital laser dynamic caustics was used,a series of experiments were conducted on polymethyl methacrylate (PMMA) using a notched semi-circular bend (SCB) specimen with a center crack of 10 mm.The results show that:the impact load was increasing before the crack initiation;until it reached the maximum 4.8KN,the crack began to initiate and propagate;the impact load was decreasing after the crack initiation.Under the impact load,the stress intensity factor at crack tip of specimen decreased rapidly,because the micro-cracks were activated;but when the cracks continued to propagate,the stress intensity factor at crack tip of specimen increased again.In all crack propagation,the velocity is almost same,but it decreased gradually when it propagated to the boundary