Correlations Among Void Shape Distributions, Dynamic Damage Mode, and Loading Kinetics
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Three-dimensional x-ray tomography (XRT) provides a nondestructive technique to characterize the size, shape, and location of damage in dynamically loaded metals. A shape-fitting method comprising the inertia tensors of individual damage sites was applied to study differences of spall damage development in face-centered-cubic (FCC) and hexagonal-closed-packed (HCP) multicrystals and for a suite of experiments on high-purity copper to examine the influence of loading kinetics on the spall damage process. Applying a volume-weighted average to the best-fit ellipsoidal aspect-ratios allows a quantitative assessment for determining the extent of damage coalescence present in a shocked metal. It was found that incipient transgranular HCP spall damage nucleates in a lenticular shape and is heavily oriented along particular crystallographic slip directions. In polycrystalline materials, shape distributions indicate that a decrease in the tensile loading rate leads to a transition to coalesced damage dominance and that the plastic processes driving void growth are time dependent.
KeywordsVoid Growth Damage Site Spall Strength Void Shape Spall Damage
This research work was funded by LANL under LDRD #20060021DR and LDRD-DR #20100026 and by the Department of Energy; NNSA; under SSAA Grants #DE-FG52-06NA26169, DE-FG52-10NA29653, DE-NA0002005, and DE-NANA0002917; and APS General User Proposal 35561. The Los Alamos National Laboratory is operated by LANS, LLC, for the NNSA of the US Department of Energy under Contract DE-AC52-06NA25396. Eric Loomis, Pat Dickerson (LANL), Damian Swift (LLNL), David Wright, and Dallas Kingsbury (ASU) are thanked for their help during the various phases of the research work. Access to the TRIDENT Facility & Electron Microscopy Laboratory at LANL, Pavel Shevchenko at APS 2-BM, as well as the Center for High Resolution Electron Microscopy and the Mechanical Testing Laboratory at ASU is gratefully acknowledged.
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