BRANCHING OF A FAST CRACK IN POLYMERS

Crack branching in Araldite D and Homalite-911 was studied using a modified Cranz-Schardin type high speed camera which provided simultaneously taken shadow patterns and specimen-focussed images. Fracture parameters including crack velocity a, stress intensity factor K(d) and specific crack extension resistance R* were measured in the course of crack propagation. No definite critical values could be determined with one of those fracture parameters for the onset of crack branching. Instead, the product R*a, i.e., energy per unit crack width per unit time, was found to have a critical value for the branching.