Spall fracture: Mechanical and microstructural aspects

A setup for plate impact experiment has been developed at LPMM-Metz to study dynamic fracture at strain rates up to 10(6) s(-1). Spalling is a specific kind of fracture which is loading history dependent. It may depend on temperature, microstructure and time of loading. This paper reports measurements of spall stress at different loading times. An aluminum alloy of the series 7000 and a high strength steel, materials which have diametrically different microstructures, have been tested in order to determine the spall stress vs loading time and also to characterize the influence of microstructure. Optical microscopy and scanning electron microscopy observations illustrate the mechanisms which lead to mixed brittle/ ductile spall fracture. To complete this experimental and fractographic study, a cumulative fracture criterion is analyzed. Also literature data are included in order to understand the effect of the initial temperature on the incipient spall stress. (C) 1999 Elsevier Science Ltd. All rights reserved.