Post-test characterization of the hardness and microstructure of copper rails from a 9 MJ electromagnetic launcher

Following a test series consisting of sixty-seven experiments, the rails from a 90 mm diameter /spl times/10 m long launcher were removed for metallurgical characterization. The rails were machined from OFHC copper extrusions. The measured Brinell hardness values of the rails ranged from HB 60 to HB 86. The starting material had a hardness of HB 86. Observed values increased from the breech up to a distance of approximately 4 m and tended to decrease and level off beyond 4 m. These hardness values are normal for worked OFHC copper, falling between those for fully annealed (HB 34) and cold rolled (HB 91) conditions. The compressive flow strength of the as-received material was determined to be /spl sigma//sub f/=331 /spl epsi//sup 0.12/ MPa. Extensive cratering and hypervelocity gouging damage was observed except in the regions 1 m from the breech end and between 7.5 and 10 m. The microstructure of the as-received rail material was fully dense and equiaxed and the average grain size was 100 /spl mu/m.>