Dimple fracture under short pulse loading

Void nucleation, growth and coalescence play a central role in the dimple fracture of metals. The work of cleavage fracture in a cracked steel specimen under short pulse loading by Homma et al. (Cleavage fracture under short stress pulse loading at low temperature. ASTM STP 1130. Philadelphia: American Society for Testing and Materials, 1992. p. 37–49), showed that the cleavage fracture takes place in the circumstance of very limited plastic deformation near a crack tip, and the cleavage crack initiation can interact with the short impulsive loading life. In dimple fracture mode, more significant interaction with impulsive stress intensity life can be likely anticipated. Under this prospect, this work carried out experiments for aluminum alloy 7075-T651 specimens subjected to impulsive stress intensity of 20, 40 and 80 μs duration. Fracture surfaces were observed by a scanning electron microscope (SEM) to examine dimple fracture ahead of a crack tip. The critical stress intensity for the crack initiation gradually increases as the pulse duration decrease from 80 to 40 μs and steeply arises when the stress intensity pulse duration decreases to 20 μs.