After the propagation of compressional shocks in a two-dimensional (2D) Yukawa solid, the structure and dynamics of the postshock region are investigated using molecular dynamical simulations. When the compressional speed is significantly higher than 0.354a0ωpd, the postshock region melts completely; however, when this compressional speed is much lower than 0.283a0ωpd, the postshock region is still in the solid state. It is found that, when the compressional speed 0.283a0ωpd≤vleft≤0.354a0ωpd, from the calculated Voronoi diagram, the postshock region clearly exhibits the coexistence of the solid close to the compressional boundary and the liquid in the other part. The calculated averaged kinetic temperature profile in the postshock region exhibits a roughly linear increase in front of the compressional boundary, and the spatial portion whose averaged kinetic temperature is lower than the melting point agrees with the solid region determined directly from the Voronoi diagram. This spatial variation trend of the averaged kinetic temperature in the postshock region is attributed to the dynamical heterogeneity of the 2D Yukawa systems, which is more severe when the mean kinetic temperature is around the melting point. Test runs with various conditions further confirm this interpretation.

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Molecular dynamical simulations are performed to systematically investigate the elastic–plastic transition of compressional shocks in a perfect two-dimensional Yukawa crystal. Following the tradition in the theory of elasticity, a stress tensor is used to characterize the state of stress of the simulated systems, and then the variation of the maximum shear stress in the postshock region is precisely obtained. It is found that, as the compression level gradually increases in the 2D Yukawa crystal, the maximum shear stress first increases linearly with the compressional speed until it reaches its extreme value, then decreases drastically to a much lower level. This obtained extreme value of the maximum shear stress is just at the elastic–plastic transition point, corresponding to one-half of the yield stress, which represents the ability to resist the maximum applied shear for the simulated Yukawa crystal. Our calculated Voronoi diagrams and pair correlation functions in the direction perpendicular to the shock compression further confirm this elastic–plastic transition point. It is also found that the critical compressional speed of the elastic–plastic transition point increases with the coupling parameter and decreases with the screening parameter of the 2D Yukawa crystal.

The TH−PH Hugoniot curves of compressional shocks in 2D Yukawa systems are derived from the combination of the Rankine–Hugoniot relation around the shock front and the universal relationship for the temperature in the postshock region. From the equation of state of 2D Yukawa liquids, the equilibrium melting curve for 2D Yukawa systems is derived using the two variables of the temperature T and the pressure P. It is found that the obtained TH−PH Hugoniot curves are intercepted by the equilibrium melting curve, indicating the existence of shock-induced phase transition at these crossing points. To confirm this prediction, molecular dynamical simulations of 2D Yukawa systems of κ=0.75 for the conditions around the crossing point are performed. In the postshock region, the calculated various diagnostics of static structural measures, like the Voronoi diagram, the defect ratio, the probability distribution of the shape factors ξ, the pair correlation function g(r), and the static structure factor S(q), suggest that, for our studied system, the shock-induced melting happens when the compressional speed of the boundary is 0.212a0ωpd<vleft<0.283a0ωpd, the same as the prediction from the crossing point.