Crack velocity and acceleration effects on the dynamic stress intensity factor in polymers

Dynamic crack propagations in PMMA and epoxy specimens were studied using the method of caustics in combination with a Cranz-Schardin type high-speed camera. Single-edge-cracked tensile specimens were fractured under pin-loading conditions so that cracks could experience acceleration, deceleration and re-acceleration stages in one fracture process. The dynamic stress intensity factor K_ID, crack velocity ȧ and acceleration ä were evaluated in the course of crack propagation to examine the effects of ȧ and ä on K_ID. Results showed that ȧ and ä were important factors in changing the values of K_ID, and for a constant ȧ the decelerating crack had a larger value of K_ID than the accelerating or re-accelerating crack. Also, it was found that K_ID could be expressed as two parametric functions of ȧ and ä for PMMA and epoxy specimens.