SUMMARY
The objective of this work has been to investigate the applicability of gas guns to study the armature-rail interface wear characteristics relevant to railgun operations. The approach involved developing constitutive models for armature materials (aluminum 6061) and oxygen-free high-thermal conductivity copper as the rail material. Taylor rod-on-anvil impact experiments were performed to validate constitutive strength models by correlating predictions of simulations in AUTODYN with experimental observations. An optical comparator was used to discretize the cross sectional profile of each rod-shaped sample. Parameters of the Johnson-Cook strength model were adjusted to match profiles from simulations with profiles from impact experiments. The fitted parameters were able to give overall deformed length and diameter values within 2% of the observed data. Additional simulations were then used to design geometry involving cylindrical rods of armature material accelerated through a concentric cylindrical die made of copper, to emulate the interface wear effects produced in a railgun. Experiments were conducted using both the 7.62mm and 80mm diameter gas guns. Microstructural analysis was conducted on interfaces of the recovered samples. Hardness measurements were also performed along the interface layer to evaluate the structure formation due to solid-state wear or melt formation. The stress- strain conditions resulting in the observed microstructural effects were correlated with predictions from simulations performed using the validated material models. The overall results illustrate that the stress-strain conditions produced during acceleration of Al through hollow concentric Cu die, result in interface deformation and wear characteristics that are influenced by velocity. At velocities less than 800m/s, interface wear leads to formation of layer dominated by solid-state alloying of Cu and Al, while higher velocities produce a melted and re-solidified aluminum layer.