Microstructural Effects on Damage Nucleation in Shock-Loaded Polycrystalline Copper
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Polycrystalline copper samples with varying thermomechanical histories were shock loaded to induce spall via laser-driven plate impacts at low shock stress (<6 GPa). Electron backscattering diffraction was used to obtain statistics on grain boundary (GB) misorientations within the spall plane and at all GBs that contained damage. Specimens with pre-existing plastic deformation showed dominant intergranular damage at boundaries in the 25 to 50 deg misorientation range, while heat-treated samples had mixed trans- and intergranular damage with a lessened misorientation influence at damaged GBs. 3-D X-ray tomography data were used to analyze global volume statistics and qualitatively inspect the shape of voids present in samples of varying thermomechanical histories. It was found that annealed samples had a mixed mode of spherical- and sheet-like voids, indicative of trans- and intergranular damage, respectively, and the microstructure with the highest number of Σ3 twin boundaries had the highest concentration of spherical voids. Data from a plastically pre-strained sample showed a dominance of needle- and sheet-like voids, indicating primarily intergranular damage due to the higher strength of the bulk material forcing the damage to nucleate at weaker defects, in this case GBs.
KeywordsGrain Boundary Misorientation Angle Spall Strength Void Shape Thermomechanical History
This research work was funded by LANL under LDRD # 20060021DR, and by the Department of Energy, NNSA, under SSAA Grants # DE-FG52- 06NA26169, DE-FG52-10NA29653., and DE-NA0002005 and APS General User Proposal 35561. 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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