Effects of Metallurgical Parameters on Dynamic Fracture

Abstract

The effects of systematically varying three common metallurgical parameters on the fracture pattern caused by impact loading have been studied using optical and electron microscopy. 1) Increasing dislocation densities were produced in pure copper specimens by compression prior to impact testing. The dynamic fracture strength increased and the total amount of strain induced by the impact loading, decreased for larger pres trains. The fracture surface of the copper showed typical ductile fracture morphology. 2) Decreasing the stacking fault energy using alloys of copper with up to 7 weight percent aluminum, was found to increase the dynamic fracture strength and the twin density resulting from the impact loading. Recovered fracture surfaces showed typical morphology of twin markings. 3) The state of precipitation in two age hardenable aluminum alloys was found to affect the dynamic fracture behavior. Samples of 2024 aluminum alloy showed a continuously increasing level of spall damage with increasing aging times. Samples of 6061 aluminum alloy on the other hand displayed decreasing fracture damage for aging times up to the maximum hardness condition and increasing fracture damage for longer aging times. The fracture surface morphology was typically ductile in nature and did not vary in appearance among the samples with the different precipitation states studied.