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Spall damage in shocked loaded FCC metals has been shown to be affected by the density of intrinsic defects such as grain boundaries and triple joints, which can serve of microstructural weak links for damage localization. As spall damage nucleates and grows, intrinsic length scales associated with the damage process, i.e., void size and spacing, are likely to be affected via interactions with microstructural length scales such as grain size. Understanding and quantifying these effects is a first step to formulate accurate homogenized models for spall damage that are also microstructurally aware. In this work, high purity copper single crystals, multicrystals and polycrystals were shock-loaded using flyer-plate impacts under conditions leading to incipient/intermediate spall. Specimens were soft recovered, and the resulting spall damage was characterized via X-ray tomography at the Advanced Photon Source, while the microstructure and its correlation with spall damage localization were characterized using scanning electron microscopy via secondary electron imaging and electro backscattered diffraction. The tomography data was used to study the statistics of damage length scales including void size and nearest neighbor distances. These distributions were studied to estimate the appropriate sizes of representative volume elements (RVEs) based on damage length scales only. These length scales, in turn, were compared and correlated to microstructural length scales, e.g., grain size distributions, for different microstructures. Results indicate that void size and spacing distributions do change as functions of position in the sample and that under incipient spall conditions RVEs based on homogenization approaches, i.e., the smallest volume that has the same void fraction of damage as the whole scanned volume, can be significantly larger than microstructural length scales for the samples.

This work was supported by Los Alamos National Laboratory under LDRD # 20060021DR, the Department of Energy/NNSA, under DE-FG52- 06NA26169, DE-FG52-10NA29653 and DE-NA0002005, and APS General User Proposal 35561. Access to the TRIDENT Facility at LANL, the APS 2-BM beamline, as well as the Mechanical Testing Laboratory at ASU is gratefully acknowledged.