Coupled Experiment and Theory to Explore the Limits of Material Strength at High Strain Rates

Experiments to study materials at high pressure are challenging and time consumptive, therefore we turn to modeling tools to refine and predict outcomes beforehand. Efficient models balance absolute physical accuracy against approximate but computationally lightweight constitutive inputs. By using a relatively small number of high fidelity simulations we have be able to broaden the predictive power of the shock response in metals and polymers. Analysis of these simulations has produced parameterizations of material strength, which can be used as constitutive inputs for continuum hydrodynamics codes. For shocked Cu, MD simulations show a yield strength from Richmyer-Meshkov Instability(RMI) jet growth of approximately 450MPa that depends on the details of the free surface geometry. This value is close to the yield strength of 500MPa parameterized from experiments at the Dynamic Compression Sector at Argonne National Lab. The same analysis applied to MD simulations of PMMA jetting resulted in no clear determination of yield strength, implying a more complex RMI process in polymeric materials. Simulations of both materials demonstrate the need for explicit strain rate dependence for future improvements in strength models used in continuum codes.