An energy balance in crack propagation and arrest

Abstract

The data from temperature gradient double tension tests and dynamic small scale tests on two steels having different toughness levels have been utilised in a quasi-static crack arrest analysis. An energy balance approach using the total initial elastic energy progressively depleted by the absorbed fracture propagation energy predicted arrest temperatures to within 7°C of the values measured at the arrested crack tip in double tension tests. The general criterion for crack arrest including conditions where crack tunnelling by shear occurs is: R s >σ 2 iL/2E(1+a p /W) where R s is the mean impact propagation energy per unit area required for arrest; σ i is the initial applied gross section stress; L is the effective length of the whole of the structure; a p is the length of the arrested crack; W is the width; E is the elastic modulus. The above expression applies to service conditions as well as to laboratory tests. It incorporates the kinetic energy which is a means whereby the total elastic energy is made available for fracture. For linear elastic plane strain conditions with no tunnelling, the equivalent stress intensity factor K s derived from the above is: K s >σ i/(1/(2W tan( πa p /2W))+2a p /WL) 0.5. This expression can only be applied to predict arrest where L and, therefore, the total energy of the structure is low and the slope of d K/d a is negative.