Crack branching in Homalite-100 sheets

Abstract

Crack branching in Homalite-100 sheets of 1/8-in. and 3/8-in. thickness was studied by dynamic photoelasticity. Dynamic stress intensity factors, crack velocities and branching angles were measured and corresponding static stress intensity factors were determined by the method of finite element analysis. Dynamic stress intensity factors which preceded the actual branching reached a peak value of approximately three times the fracture toughness. The dynamic stress intensity factor drops prior to branching and then increases again to the maximum stress intensity factor at which point branching could occur again. Roughness of the fracture surface can be related to large dynamic stress intensity factors and crack velocities prior to branching and also after branching. Average branching angle was 26 deg. The results of this series of tests thus suggest that large dynamic stress intensity factors are necessary but not sufficient to cause crack branching.