It is of substantial scientific significance and practical value to reveal and understand the multiscale mechanical properties and intrinsic mechanisms of medium-entropy alloys (MEAs) under high strain rates and pressures. In this study, the mechanical responses and deformation mechanisms of an equiatomic CoCrNi MEA are investigated utilizing magnetically driven ramp wave compression (RWC) with a strain rate of 105 s−1. The CoCrNi MEA demonstrates excellent dynamic mechanical responses and yield strength under RWC compared with other advanced materials. Multiscale characterizations reveal that grain refinement and abundant micromechanisms, including dislocation slip, stacking faults, nanotwin network, and Lomer–Cottrell locks, collectively contribute to its excellent performance during RWC. Furthermore, dense deformation twins and shear bands intersect, forming a weave-like microstructure that can disperse deformation and enhance plasticity. On the basis of these observations, we develop a modified crystal plasticity model with coupled dislocation and twinning mechanisms, providing a relatively accurate quantitative description of the multiscale behavior under RWC. The results of simulations indicate that the activation of multilevel microstructures in CoCrNi MEA is primarily attributable to stress inhomogeneities and localized strain during RWC. Our research offers valuable insights into the dynamic mechanical responses of CoCrNi MEA, positioning it as a promising material for use under extreme dynamic conditions.

Shaped charge liners driven by MA-class high pulsed power generators are a cutting-edge technology in the field of munitions, attracting significant attention. However, existing electromagnetically driven jet formation technology is limited by imperfect theoretical knowledge and insufficient experimental validation of jet formation dynamics. To address this issue, experimental research was conducted on the collapse process of shaped liners and jet formation using the compact pulsed power generator CQ-7, along with photon Doppler velocimeter (PDV) and high-speed photography. The evolution curve of the velocity on the inner wall of the liner and the average velocity of the jet head were obtained. Based on the experimental results, a comprehensive circuit model that considers dynamic inductance and resistance was introduced. This model, in combination with the Pugh–Eichelberger–Rostoker (PER) theory, accurately describes the physical process of jet formation. The results demonstrate that conical liners can form high-speed jets if their operational parameters are optimized. For a compact pulsed power generator with low impedance, the impact of load dynamic parameters on current and liner collapse behavior cannot be ignored. The experimental results have verified the theoretical model parameters well. Finally, the verified model was used to study the dynamic processes of liner collapse and jet formation as well as the impact of the loading current on jet formation, from which significant insights were obtained.

Determination of yield strength of polymers under dynamic loading has proven to be extremely difficult. Up to now, few strength data have been obtained for polymers at strain rate above 10⁵/s. Based on the electromagnetically driven quasi-isentropic loading technique, the yield strength of polystyrene under high pressure and high strain rate was measured experimentally by pressure comparison method. In the experiment, a polystyrene window method is used to measure the in-situ particle velocity directly, which reduces the experimental error and obtains reliable high-pressure Lagrangian sound velocity and quasi-isentropic compression line. The yield stress of polystyrene under quasi-isentropic compression are measured continuously at pressure up to 4GPa and strain rate of 10⁶/s. Combined with strength data under quasi-static and intermediate strain rate loading, the strain rate effect of yield of polystyrene was analyzed. It was found that the yield strength of polystyrene has strain rate effect, but the “upturn” phenomenon was not observed. Additionally, the yield stress of polystyrene from 10^-3/s to 10⁶/s strain rate can be fitted by Eyring model, which provides a reference for the study of physical properties of polymer materials under high strain rate loading.

The studies of characteristics and load configuration of an electromagnetically driven shaped liner during the collapse process are significant for understanding its physical process deeply and guiding its application. A coupled electromagnetic–mechanical–thermal physical model was established and validated for characterizing electromagnetically driven shaped liners. The parameters of the liner structure were optimized for high velocity and strong penetration jet. The outcomes demonstrated that the current and magnetic fields concentrated on the outer surface of the liner at the beginning of loading. Subsequently, they gradually diffused in the thickness direction due to magnetic diffusion. The liner was heated and even ablated by joule heat at current density with several mega-amperes per centimeter. Under a current with a peak value of 4.4 MA and a half-cycle of 1.29 $\mu $ s, the diffusion depth of the copper liner is 0.4 mm. Within the diffusion depth, some material near the apex vaporized, while most of the area remained in a solid or liquid state. The collapse velocity increases with decreasing thickness under the same loading conditions. The current density decreases due to the increase in the diameter, and the overall velocity of the liner with a larger cone angle is smaller than that of a smaller cone angle. The tendency and law of the current density, magnetic diffusion depth, and ablation thickness on the loading surface are similar. Furthermore, the ablation near the apex with a larger cone angle is more severe. A shaped liner with a small cone angle is suitable for obtaining a jet with high velocity and strong penetration.