Line VISAR and post-shot metallography comparisons for spall analysis

Key to understanding spallation phenomena is determining the spatial and temporal distribution of failure nucleation. We have conducted a series of spallation experiments on copper and tantalum using a line-imaging VISAR (LIV), which measures the velocity histories at a continuous series of points in a dynamic experiment. In these experiments on carefully characterized copper and tantalum, we attempted to produce an incipient spall condition while monitoring with LIV. Pre-shot sample characterization included spatially resolved mapping of grain locations and orientations by electron backscatter diffraction (EBSD). The samples were then soft-recovered and sectioned along the same line as monitored by the LIV. We sought to determine whether the sample distension inferred from the LIV data agree with that measured in the sectioned post-shot samples, and whether the spatial variations in the LIV data correspond more closely to failure structure on the spall plane or to near-surface grain structure (and consequent wave processing). Two experiments yielded ∼1 mm spall separation; the other two are close to incipient spall conditions.