Microstructural Modifications after Small Charge Explosions in Aluminum and Copper Targets

Metals exposed to explosions undergo several macro and micro changes. At the microstructural level slip bands or mechanical twins, caused by the pressure and temperature wave, can be detected. Twinning or slip occurs depending on the metal stacking fault energy, the blast wave pressure and the deformation rate. An experimental campaign was performed on different FCC metals. Results concerning OFHC Copper and AA 2014 aluminum alloy are presented herein and compared with previous results concerning AISI 304Cu stainless steel and a 18 carat gold alloy. Specimens exposed to small charge explosion (50 or 100 g of plastic explosive) were analyzed by optical microscopy and by X-ray diffraction. Microstructural plastic deformation marks were detected and their possible attribution either to mechanical twinning or to cross slip is discussed on the basis of the X-ray diffraction patterns. The detectability target-to-charge distance limit, and hence the critical stress for microstructural changes are evaluated.