Fracture Behavior under Impact.
Annual rept. no. 2, Feb 82-Jan 83,
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 directly loaded by an impinging projectile or by a base plate which is accelerated by a 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 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 compare to corresponding static fracture toughness data. Within the second year of the three years research project many experiments of the proposed main investigations have been carried out First the dependence of the impact fracture toughness KId on loading rate has been investigated. Specimens from the Araldite B with single edge cracks have been tested under base plate - and under direct impact loading conditions. Within the range of loading rates achieved so far, the measured impact fracture toughness KId do not show a dependence from loading rate.