Measurement of elastic-plastic shock propagation and phase transition using multi-point time-gated Raman spectroscopy

This study utilizes in situ multipoint time-gated Raman spectroscopy to simultaneously measure molecular structural changes along with the corresponding changes in mechanical properties in shock-compressed sucrose crystals. The measurements successfully captured full-field shock compression wave propagation, leading to visualization of the elastic and plastic phases of the shock compression. The shock wave initially generates an elastic front, increasing pressure and temperature, followed by a larger elastoplastic zone marked by peak shifts and new peaks. The crystal then transitions through a metastable phase before undergoing shock-induced phase transformation, eventually reverting to a stable phase, which differs from its original undeformed state. The Raman measurements focused on CH and CH₂ peak shifts under shock loading, enabling the calculation of pressure (∼5 GPa) and temperature (>1000 °C) spatial maps as a function of time during shock wave propagation. For an impact velocity of 1.2 ± 0.1 km/s, the width of the shock pulse was determined to be 125 ± 5.2 μm, and the elastic shock velocity was 6.25 ± 0.52 km/s. The energy density dissipation, derived from shifts in the CH and CH₂ stretch modes, was 6.67 ± 2.11 × 10⁷ kJ/m³ and evenly distributed relative to the pressure and temperature fields. The primary mode of failure was found to be micromechanical crushing by the forward shock wave; however, in some cases, the compaction followed by crushing allowed for the return of a rarefaction wave, leading to separation along the spall plane.