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We investigate spallation of polycarbonate under plate impact loading. The Hugoniot equation of state up to ∼1.3GPa (corresponding to a peak particle velocity ∼380m/s) is obtained, and spall strength and corresponding strain rates are determined at peak shock stresses up to ∼2.4GPa (corresponding to a peak particle velocity ∼600m/s). With increasing shock strength, the transition from strain-hardening to softening at shock states occurs as a result of shock heating; spall strength remains approximately constant, followed by a rapid drop upon strain softening. Release/tensile melting occurs at higher impact velocities. Three-dimensional void configurations of the postmortem samples are obtained via X-ray computerized tomography. The small voids are flat and curved for low-speed shots but become ellipsoidal for high-speed shots, and their coalescence leads to different shapes likely due to different damage mechanisms.

High‐brightness coherent ultrashort X‐ray free‐electron lasers (XFELs) are promising in resolving nanoscale structures at the highest temporal resolution (∼10 fs). The feasibility is explored of resolving ultrafast fragmentation of liquids at the nanoscale with single‐shot small‐angle X‐ray scattering (SAXS) on the basis of large‐scale molecular dynamics simulations. Fragmentation of liquid sheets under adiabatic expansion is investigated. From the simulated SAXS patterns, particle‐volume size distributions are obtained with the regularization method and average particle sizes with the weighted Guinier method, at different expansion rates. The particle sizes obtained from simulated SAXS are in excellent agreement with direct cluster analysis. Pulse‐width effects on SAXS measurements are examined. The results demonstrate the feasibility of resolving the nanoscale dynamics of fragmentation and similar processes with SAXS, and provide guidance for future XFEL experiments and data interpretation.