Dynamic measurement of the J integral in ductile metals: Comparison of experimental and numerical techniques

Experiments and analyses designed to develop an extension of the method of caustics to applications in dynamic, elastic-plastic fracture mechanics are described. A relation between the caustic diameter, D, and the value of the J integral was obtained experimentally and numerically for a particular statically loaded specimen geometry (three point bend) and material (4340 steel). Specimens of the same geometry and material were then loaded dynamically in impact. The resulting caustics, recorded using high speed photography, were analyzed on the basis of the J versus D relation to determine the time history of the dynamic value of J, J^d(t). The history of J^dthus obtained is compared with good agreement to an independent determination of J^d(t) based on a two-dimensional, dynamic, elastic-plastic finite element analysis, which used the experimentally measured loads as traction boundary conditions.