Following previous experimental evidence of growth and arrest of Richtmyer-Meshkov instabilities in copper, we have used the CTH shock physics code to study and calibrate the effects of material strength at high strain rates. Highly resolved one and two-dimensional simulations were performed using the Johnson-Cook (JC), Mechanical Threshold Stress (MTS), and Preston-Tonks-Wallace (PTW) strength models. The one-dimensional simulations utilized a prescribed homogeneous deformation strain path covering strain rates observed in previous hydrodynamic instability experiments. Spall was modeled using a nominal threshold pressure model (PFRAC) and we use the Mie-Gruneisen equation of state to estimate the volumetric response of the experiments. Our results show good qualitative and quantitative agreement between numerical estimates and prior experiments in the strain rate regimes of interest.
With the increasing use of hydrocodes in modelling and system design, benchmarking of software against experiments has become even more vital. While substantial work has been done in this regard, comparisons with temperature data within dynamic experiments are sparse due to experimental limitations. However, novel developments in measurement techniques has enabled the in-flight acquisition of hypervelocity projectile temperature, providing a new source for validation. This is achieved by tracking the decay of an induced magnetic field which is related to conductivity and further correlated to material temperature. As such, an AC-14 bare shaped charge with a copper lining is simulated using CTH, and benchmarked against experimental temperature results observed by Uhlig and Hummer. Particular attention was given to the slug temperature profiles after separation, and the effect of varying equation-of-state and strength models. Simulations are in agreement with experimental results, with a best case of under 2% error between the observed and simulated temperatures for this shaped charge setup. This varied notably (around 20% variance) depending on strength model. Jet structures compare well with radiographic images and are consistent with ALEGRA simulations previously conducted. SAND2017-3686C.
Code validation against experimental data is vital in building confidence for the use of simulation software in modeling and system design. Temperature data is of particular interest in the study of hypervelocity impact, however the experimental measurement of temperature in such a regime is difficult. Novel developments in measurement techniques have enabled the measurement of in-flight hypervelocity projectile temperature. This is done by saturating the projectile with a magnetic field, in flight, and tracking its decay, which is related to material conductivity and therefore temperature. This study seeks to use CTH to computationally model experiments conducted by Uhlig and Hummer in which in-flight temperature of an explosively formed projectile (EFP) was measured. Comparing CTH results to physical observations serves as a benchmark for the accuracy of internal temperature calculations. Transient temperature results were shown to vary greatly with chosen strength model, with highest accuracy (3.4%) being attained with the Johnson Cook model. These results were on the same order as previously done ALEGRA simulations, though with differing variations between strength models, and EFP structure matches well with experimental x-ray. SAND2017-3687C.