Numerical study of rate-dependent strength behavior under ramp and shock wave loading

The main objective of the current study was to gain a detailed understanding on the rate-dependent strength behavior under ramp and shock wave loading. A forward, numerical-simulation-based cause and effect analysis was used to address the research objective. The apparent strength associated with shock and ramp wave loadings with different risetimes and shapes was investigated. It was shown that intrinsic material strength could vary with pressure, temperature, and deformation history, but the apparent strength, which was larger than the intrinsic strength, was a result of the interaction between the rate sensitivity of the strength and the rate of the external loading. The degree of interaction led to different levels of mechanical and thermal dissipations and their partition, which was manifested by different temperature, stress, and deformation histories. The knowledge and foundation established in this study should provide some guidance in the proper interpretation and analysis of the measured wave profiles obtained from ramp and shock wave experiments, instead of simply by trial and error of applying an arbitrary model without a sound physical justification. As also demonstrated in this study, different types and degrees of material dissipations result in much more dramatic changes in temperature than mechanical response. In other words, temperature could provide a direct measurement of material dissipation and provide a distinct signature of the actual material response. This study also shows that by varying the risetimes and/or shapes of ramp waves, different strain rate histories can be produced. Thus, the ramp wave experiment is potentially a very effective tool to investigate the rate sensitivity of material strength.