Femtosecond quantification of void evolution during rapid material failure

Coakley, James and Higginbotham, Andrew and McGonegle, David and Ilavsky, Jan and Swinburne, Thomas D. and Wark, Justin S. and Rahman, Khandaker M. and Vorontsov, Vassili A. and Dye, David and Lane, Thomas J. and Boutet, Sébastien and Koglin, Jason and Robinson, Joseph and Milathianaki, Despina (2020) Femtosecond quantification of void evolution during rapid material failure. Science Advances, 6 (51). eabb4434. ISSN 2375-2548 (https://doi.org/10.1126/sciadv.abb4434)

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Understanding high velocity impact, and the subsequent high strain rate material deformation and potential catastrophic failure, is of critical importance across a range of scientific and engineering disciplines that include astrophysics, materials science and aerospace engineering. The deformation and failure mechanisms are not thoroughly understood, given the challenges of experimentally quantifying material evolution at extremely short time-scales. Here, copper foils are rapidly strained via picosecond laser ablation and probed in situ with femtosecond x-ray free electron (XFEL) pulses. Small angle x-ray scattering (SAXS) monitors the void distribution evolution while wide angle scattering (WAXS) simultaneously determines the strain evolution. The ability to quantifiably characterize the nanoscale during high strain rate failure with ultrafast-SAXS, complementing WAXS, represents a broadening in the range of science that can be performed with XFEL. It is shown that ultimate failure occurs via void nucleation, growth and coalescence, and the data agree well with molecular dynamics simulations.