Investigations into rapid uniaxial compression of polycrystalline targets using femtosecond X-ray diffraction
D McGonegle and A Higginbotham and E Galtier and EE McBride and MI McMahon and D Milathianaki and HJ Lee and B Nagler and SM Vinko and JS Wark, 18TH APS-SCCM AND 24TH AIRAPT, PTS 1-19, 500, 112063 (2014).
Although the pressures achievable in laser experiments continue to increase, the mechanisms underlying how solids deform at high strain rates are still not well understood. In particular, at higher pressures, the assumption that the difference between the longitudinal and transverse strains in a sample remains small becomes increasingly invalid. In recent years, there has been an increasing interest in simulating compression experiments on a granular level. In situ X-ray diffraction, where a target is probed with X-rays while a shock is propagating through it, is an excellent tool to test these simulations. We present data from the first long-pulse laser experiment at the MEC instrument of LCLS, the world's first hard X-ray Free Electron Laser, demonstrating large strain anisotropies. From this we infer shear stresses in polycrystalline copper of up to 1.75 GPa at a shock pressure of 32 GPa.
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