Experiments to measure gouging threshold velocity for various metals against copper

Hypervelocity gouging is a form of damage that can occur to surfaces in sli ding contact at high relative velocity. Gouges, which are in the form of te ardrop-shaped craters, have been observed on rocket sled tracks, in light g as gun barrels, and in the bore of railguns. One aspect of gonging that has not been adequately explained is the existence of a minimum velocity (or t hreshold velocity) for a given material pair below which gonging does not o ccur. This paper reports a series of experiments to test the hypothesis tha t the onset of gouging is governed by the hardness of the harder material a nd by the density and sound speed of both materials. In the tests, samples of various metals were accelerated to 2.2 km/s while in direct sliding cont act with CD110 copper rails. The samples were carried in a Lexan polycarbon ate forebody, modified to apply normal loads of 40 - 80 MPa to the sample/r ail interface, The portion of the armature directly in line with the sample s was cut away to avoid contaminating the gouge track. Visual inspection of the resulting gouges was used to establish a gouging threshold for each me tal The tests were conducted in the 40-mm square bore electromagnetic launc her at the Institute for Advanced Technology (IAT). Metals tested include A ISI 1015 steel, silver, molybdenum, pure copper, tungsten, nickel, magnesiu m, and 7075 aluminium alloy. The results of the experiments show the existe nce of a straight line fit between hardness of the harder material and the shock pressure for a normal collision at the gouging threshold velocity.