Dynamics of the onset of damage in metals under shock loading

This paper presents results on the dynamics of damage in copper under incipient spall conditions for multicrystalline specimens. Specimens were annealed from polycrystalline material to reduce the number of grain boundaries the shock wave traverses in passing through the specimen. The specimens incorporated unique fiducials that permit accurate correlation of pre-shot characterization of the grain orientations, grain size etc. with the location of the dynamic diagnostics and with post-shot metallography. The dynamic diagnostics - Transient Imaging Displacement Interferometry (TIDI), point VISAR, line VISAR - were all precisely aligned on the specimen surface to view regions of interest revealed in the pre-shot characterization. Initial analyses demonstrate the wealth of information obtained from this experimental approach. Examples include observation that regions in the surface micro structure most likely to be damaged based on pre-shot characterization show some of the largest displacements during the shock-loading. Post-shot microscopy shows damage in the same places. Another observation is there appears to be localized plastic deformation that occurs during the first compression wave which then remains and evolves through several cycles of compression and release from the spall plane.