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Richtmyer–Meshkov instability developed at a solid–vacuum interface after reflection of a shock wave is studied using the smoothed particle hydrodynamics (SPH) method. SPH simulations are performed for aluminum, copper, and tantalum samples with free surfaces having machined grooves of sinusoidal shape. The obtained simulation results agree well with the experimental data for different loading regimes. Our simulations demonstrate three regimes of material response to shock loading, where conditions depend on the yield strength for a given strain rate. First, at weak elastic shocks, the grooved surface experiences shear oscillations only. Then, a more intense shock loading produces plastic strain resulting in a plastic spike with the limited run from the surface. It is found that after the arrest of the plastic motion, the formed spike oscillates with the same period as in the elastic regime. Finally, the heavy load produces the unlimited growth of plastic or liquid jet, which leads to its fragmentation at later times. The transition from limited to unlimited jet growth depends on the geometry of the corrugated surface. We estimate the critical amplitude of corrugations required for unlimited spike growth. The used simulation techniques can provide the more accurate mechanical properties of materials to achieve a better agreement. [ABSTRACT FROM AUTHOR]

Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation. [ABSTRACT FROM AUTHOR]

Intense laser radiation leads to irreversible changes in the crystal structure of a target, which are used in laser shock peening technologies. Processes determining the thickness of the residual deformation layer and related residual stresses are studied in this work. It is known that the end of peening is caused by the decaying of the laser shock wave. New information on the transformation of the wave from the elastoplastic to elastic propagation mode under a picosecond impact is obtained. The elastic shock wave is inefficient for peening. The classical configuration with a plastic jump and an elastic precursor ahead of it turns out to disappear during transformation. In this case, the leading edge of the expanding plastic layer gradually decreases its velocity below the bulk velocity of sound, is smeared inside the rarefaction wave, and stops. [ABSTRACT FROM AUTHOR]