Metallographic Examination of Thermal Effects in Hypervelocity Gouging

In this work, a gouged section of 1080 railroad rail steel is examined using metallographic techniques to characterize the nature of the damage. The gouging was performed by a rocket sled at Holloman Air Force Base, riding on VascoMax 300 steel shoes at 1.5 to 3.0 km/sec. Similar in approach to Gerstle, et al. [1], the damaged rail is evaluated in detail to examine material phase changes, shear bands, and heat effects. The results can be compared to samples of the virgin material, machined and prepared exactly as the rail and shoe are prior to the Holloman AFB High Speed Test Track (HHSTT) runs. The gouged section was examined longitudinally and in a transverse manner using optical microscopy and a Scanning Electron Microscope (SEM). Pictures are presented of the resulting microstructure. Comparisons to the virgin material confirm material mixing consistent with a high energy gouging event. In addition, the material phase change evident in this approach allows us to estimate the non-equilibrium thermal conditions present during the formation of the gouge. The creation of shear bands, predicted by the previous modeling efforts, is also confirmed.