Fracture Behavior under Impact.
Semi-annual progress rept. no. 2, Feb-Jul 82,
FRAUNHOFER-INST FUER WERKSTOFFMECHANIK FREIBURG (GERMANY F R)
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The physical behavior of cracks under impact loading is investigated. Single edge cracks or arrays of multiple cracks in rectangular specimens are considered. The specimens are loaded by time dependent tensile stress pulses moving perpendicular to the crack direction. The specimens are either directly loaded by an impinging projectile or by a base plate which is accelerated by the projectile. The specimens are made from a transparent model material or a high strength steel. The initial crack lengths and impact velocities are varied throughout the experiments. Utilizing the shadow optical method of caustics in combination with high speed photography, the dynamic stress intensity factors at the tip of the crack are measured as functions of time during the impact event. The critical value of the dynamic stress intensity factor at onset of rapid crack propagation, i.e. the dynamic fracture toughness KId, is determined and discussed with regard to the time tf at which the crack becomes unstable. The results are compared with corresponding static fracture toughness data.