This work compared the effects of modeling grain structure in hypervelocity impact simulations. Comparisons of strain rate at failure (fragment size) and material temperature were made between a suite of simulations performed with the standard bulk modeling structure and one in which individual grains were modeled. Smaller fragments or higher temperatures are needed to match EO/IR signatures from observed impacts. Results from the various studies described herein indicate that strain rate at failure is influenced primarily by projectile size, impact velocity, and material porosity. Material temperature is predominantly influenced by impact velocity and porosity; not by projectile size. Changes to the material properties within grains tended to affect lower strain rates only, but material interfaces (here, manifested as material porosity) drastically increased strain rate at failure and material temperatures. Higher strain rates are likely to produce smaller debris fragments, which, along with hot debris may help provide evidence supporting the generation of sub-micron fragments currently required by many EO/IR predictive models to successfully compare with observed hypervelocity impacts. Future work will focus on extending the study to three dimensions, assessing more realistic grain aspect ratios, and simulating other types of interfaces such as inclusions and dislocations.
With the increasing use of hydrocodes in modeling and system design, experimental benchmarking of software has never been more important. While this has been a large area of focus since the inception of computational design, comparisons with temperature data are sparse due to experimental limitations. A novel temperature measurement technique, magnetic diffusion analysis, has enabled the acquisition of in-flight temperature measurements of hyper velocity projectiles. Using this, an AC-14 bare shaped charge and an LX-14 EFP, both with copper linings, were simulated using CTH to benchmark temperature against experimental results. Particular attention was given to the slug temperature profiles after separation, and the effect of varying equation-of-state and strength models. Simulation fidelity to experiment was shown to greatly depend on strength model, ranging from better than 2% error to a worst case of 22%. This varied notably depending on the strength model used. Similar observations were made simulating the EFP case, with a minimum 4% deviation. Jet structures compare well with radiographic images and are consistent with ALEGRA simulations previously conducted. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. SAND2017-10009C.
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.
This paper details modeling of metal fragmentation of pipe-bomb configurations using the Euler-Lagrange code Zapotec. Zapotec couples the hydrocode CTH with the transient-dynamics finite element code Sierra/SM (also known as Presto) through a step-wise interchange of geometry, state data, and pressure. In this work, three experimental studies of pipe-bomb configurations were simulated using Zapotec, where the metal case was modeled using finite elements and the explosive was modeled with CTH. In the three examples, experimental and simulated debris distributions and early-time debris velocities generally showed excellent agreement. These studies both help build confidence in the use of Zapotec for simulating structural response under shock loadings.