The crack-branching velocity

Abstract

A resistance grid technique has been used to measure the acceleration of brittle cracks. The measurements show that crack-branching can occur over a range of velocities in glass. For perspex, the terminal velocity was almost reached prior to crack-branching and for a ‘Pitho’ tool steel that had been oil-quenched and tempered the crack often ran at an approximately constant high velocity for a considerable distance before crack-branching occurred. These differences are explained by considering the detailed mechanisms of crack-branching. The authors would like to thank Professor N. J. Petch for providing laboratory facilities for the work and for constructively criticizing the manuscript. Also, they wish to thank The Science Research Council for financial support and Dr. L. Molyneux for the loan of the oscilloscope.