Effects of microstructure on spall damage localization in shock loaded copper multicrystals

Correlations between damage and local microstructure were investigated in multicrystalline copper samples via impact tests conducted with laser-driven plates at low pressures (2-6 GPA). The copper samples had a large grain size as compared to the thickness, which was either 200 or 1000 μm, to isolate the effects of microstructure on the local response. Velocity interferometry was used to measure the bulk response of the free-surface velocity of the samples to monitor spall tensile failure. Electron Backscattering Diffraction (EBSD), both in-plane and through-thickness, was used to relate crystallography to the presence of porosity around microstructural features such as grain boundaries and triple points. A transition between transgranular and intergranular damage was observed as the grain size was reduced from 230 μm to 150 μm in thin samples, whereas both modes were observed in thick specimens (450 μm grain size). Potential sites for preferred damage nucleation and strain localization were identified in terms of their crystallography via statistical sampling in serial sectioned specimens. Results indicate that grain boundaries with misorientation angles larger than 30° and close to triple and quadruple points are the preferred locations for intergranular damage localization in these samples.