Effects of EOS and constitutive models on simulating copper shaped charge jets in ALEGRA

Metallic shaped charge jets (SCJ) have been studied for many decades across multiple communities for applications ranging from military warheads to earth penetrators for accessing oil-rich areas [1]. Researchers have had varied success in modeling these jets using simulation codes such as CTH, ALEGRA, and ALE3D. Recently, a large amount of work has been performed at the US Army Research Lab investigating the behavior of jets with increasingly sophisticated experimental diagnostics. Advances in computational resources, code enhancements, and material models have allowed us to model jets and probe uncertainties caused by algorithms, equations of state (EOS), constitutive models, and any of the available parameters each one provides. In this work we explore the effects that various EOS and constitutive models have on the development and characteristics of a 65-mm diameter, 2D copper SCJ using the Sandia National Laboratories’ multiphysics hydrocode, ALEGRA [2]. Specifically, we evaluate the tabular SESAME 3320 [3], 3325 [4-5], and 3337 [6] EOS models, analytic EOS (ANEOS) 3331 [7], as well as the Johnson-Cook (JC) [8], Zerilli-Armstrong (ZA) [9], Preston-Tonks-Wallace (PTW) [10], Steinberg-Guinan-Lund (SGL) [11-12], and Mechanical Threshold Stress (MTS) [13] constitutive models. Note that while the SGL model supports rate-dependence, there is no current characterization for copper, thus we are using rate-independent version. We do not consider the MieGrüneisen equation of state here as we expect parts of the jet to be near or cross into melt.

Validating Ice Impacts Using Adaptive Smoothed Particle Hydrodynamics for Planetary Defense

Understanding how a potentially hazardous object (PHO) responds to a kinetic impactor is of great interest to the planetary defense community. Target response depends upon the detailed material properties of the PHO, which may not be well constrained ahead of time. Hence, it is useful to explore a variety of target compositions for kinetic impact deflection. Previous validation efforts have focused primarily on understanding the behavior of common rocky materials, though PHOs are not exclusively composed of such material. Water ice is one material for which there has been only limited code validation against cratering experiments. It is known that comets consist of primarily icy material and some asteroids likely contain some amount of ice. Therefore, it is useful to understand the model sensitivities for ice in deflection simulations. Here we present Adaptive Smoothed Particle Hydrodynamics simulations of impacts into water ice by an aluminum projectile. We explore the sensitivities to the damage model within our code and find that the best-fit simulations of ice occur with a Weibull modulus of 12, though results can be obtained with values of the Weibull modulus near the published value of 9.59. This work demonstrates the efficacy of using an adaptive smoothed particle hydrodynamics code to simulate impacts into ice.

Experiments using a light gas gun to investigate the impact melting of gunshot residue analogues

In this set of experiments, the versatility of the University of Kent's light gas gun was utilised to obtain a selection of corroborative data regarding the formation and impact of metallic gunshot residues onto high purity silicon wafers. The results from the two experiments are presented. The first experiment investigated how the formation of metallic residues varied as gunshot residue analogues traversed through air under a range of pressures from 0.056 millibar (5.6 Pa) to 1 bar (100 kPa), using solely the energy released during primer ignition; the second involved firing a metallic powder mix of pre-determined composition (via a split-sabot) under vacuum at two velocities- 500 ms-1 and 2000 ms-1. This ensured that there was no ignition or heating of the powders, unlike the first experiment, and so the morphology of the particles collected would be solely due to impact. The residues on the substrates were then analysed using a cold Field Emission Gun Scanning Electron Microscope (FEG) and Energy Dispersive X-ray (EDX) detector. By separating the ignition process of the primers from the residue impacts, it allows for a closer look into the formation of these particles and helps determine whether their varied morphologies are due to the heating caused during the activation and combustion of the primer or whether its due to impact melting. This information can aid in the understanding of metallic particle formation in different pressure environments and give insight into the physical state of firearm residues when they impact a surface. Hydrocode modelling was also incorporated to corroborate the results observed during these experiments and gave results which mimicked the experimental data.

Validation of an Improved Contact Method for Multi-Material Eulerian Hydrocodes in Three-Dimensions

Realistic and accurate modeling of contact for problems involving large deformations and severe distortions presents a host of computational challenges. Due to their natural description of surfaces, Lagrangian finite element methods are traditionally used for problems involving sliding contact. However, problems such as those involving ballistic penetrations, blast-structure interactions, and vehicular crash dynamics, can result in elements developing large aspect ratios, twisting, or even inverting. For this reason, Eulerian, and by extension Arbitrary Lagrangian-Eulerian (ALE), methods have become popular. However, additional complexities arise when these methods permit multiple materials to occupy a single finite element.

Dynamic response of graphene and yttria-stabilized zirconia (YSZ) composites

A series of dynamic compaction studies were performed on yttria-stabilized zirconia (YSZ) and graphene composites using uniaxial flyer plate impact experiments. Studies aimed to characterize variation in dynamic behavior with respect to morphological differences for eight powdered YSZ and graphene compositions. Parameters of interest included YSZ particle size (nanometer or micrometer) and added graphene content (graphene weight percentage: 0%, 1%, 3%, 5%). Experiments were performed over impact velocities ranging between 315 and 586 m/s, resulting in pressures between 0.8 and 2.8 GPa. Hugoniot states measured appear to exhibit dependence on particle size and graphene content. Shock velocities tended to increase with graphene content and were generally larger in magnitude for the micrometer particle size YSZ. Compacted densities tended to increase as graphene content was increased and were generally larger in magnitude for the micrometer particle size YSZ samples. Resulting Hugoniot curves are compared and summarized to convey the dynamic behavior of the specimens.

A Predictive Non-Dimensional Scaling Law for the Plate Perforation of Several Aluminum Alloys by Fragment-Simulating Projectiles

An equation was previously-presented to predict the ballistic-limit velocity for the perforation of aluminum armor plates by fragment-simulating projectiles (FSP). The ballistic-limit equation was presented in terms of dimensionless parameters so that the geometric and material problem scales are identified. Previously published predictions and data for two different FSP projectile calibers (12.7 mm and 20 mm) and two different strength aluminum alloys show the scaling law to be accurate. In this paper we extend the same concept to several other alloys and show that this scaling law is predictive.

Calculation of jet characteristics from hydrocode analysis

The penetration performance of a shaped charge jet is affected strongly by factors such as straightness, stretch rate, and breakup time. Straightness is related to manufacturing tolerances, assembly techniques, and system integration features. Stretch rate and breakup time are controllable features of charge design. A higher stretch rate is desirable for short standoff performance. The stretch rate is easily altered by a change of explosive or modification of the angle with which the detonation wave sweeps the liner surface, however, an increased stretch rate generally results in a decreased breakup time. Many of the recent gains in shaped charge performance have been made possible by increasing the effective breakup time of the jet. Several models exist for calculating breakup time. They include analytic models, such as Chou & Carleone’s dimensionless strain rate model, and empirical or semi-empirical models such as Walsh’s theory and those proposed by Pearson, et al. These models can be applied to raw hydrocode calculation data and used to determine a Jet Characterization (JC) file. The JC file can then be used to perform further calculations, such as Penetration Versus Stand Off (PVSO) curves. This paper details adaptation of the Chou & Carleone model for predicting breakup time using hydrocode data. The hydrocode is used to determine the physical parameters of the jet which are then extrapolated back to a virtual origin for breakup time calculation. This results in a model that is design independent, relying on hydrocode determination of jet variables. The model implementation will be discussed, and comparisons of predicted jet characteristics will be made to test data for several charge geometries.

Shear band characteristics in high strain rate naval applications

This paper explores the dynamic behavior of HSLA 65 naval steels, specifically focusing on the initiation and growth of shear bands in quasi-static and dynamic compression experiments and how these bands affect stress-strain responses. The results indicate that the yield strength for this HSLA 65 increases from 541 ± 8 MPa for quasi-static (10-3 s-1) to 1081 ± 48 MPa for dynamic rates 1853 ± 31 s-1, and the hardening exponent increases from 0.376 ± 0.028 for quasi-static to 0.396 ± 0.006 for dynamic rates. Yield behavior was found to be associated with the onset of shear banding for both strain-rates, confirmed through visualization of the specimen surface using high-speed and ultra-high-speed cameras. For the quasi-static case, shear banding and yielding was observed to occur at 2.5% strain, and were observed to grow at speeds of upwards of 38 mm/s. For the dynamic experiments, the shear banding begins at approximately 1.18 ± 0.06% strain and these can grow upwards of 2122 ± 213 m/s during post-yield softening. Altogether, these measurements are some of the first of their kind in the open literature, and provide guidance on the critical time and length scales in shear banding. This information can be used in the future to design more failure-resistant steels, which has broader applications in construction, defense, and natural resource industries.

Numerical modeling of impacts of twisted-pair data cables

Data wire cable runs are a significant presence on the exterior of the International Space Station (ISS), and continued ISS mission support requires detailed assessment of cables due to micrometeoroid and orbit debris (MMOD) impact. These data wire cables are twisted-pair cables consisting of two 22 gauge stranded conductors inside a tight-fitting, braided-copper shield and jacket having a nominal outer diameter of 3.76 mm. Previous work has documented a total of 97 impact experiments that were performed into these cables to develop an empirical, statistical model for the failure of these cables in reliability studies; however, the experimental work left open the internal behaviors that contribute to the probabilistic findings. To address this shortcoming, numerical impact simulations have been performed to expand the understanding of the acquired dataset. This paper summarizes the dependence of impact location and speed to the penetration of wire jackets based upon particle size and provides an empirical ballistic limit equation based on the assumption that exposed conductors may lead to a short circuit. This work is consolidated with the previous experimental work for design and reliability assessments to cover projectile types, speeds and obliquities.

Transitional ballistics of electric high-velocity launchers

The high-velocity launch of a projectile is subjected to a number of disturbances which exert an influence on the flight trajectory. In the case of sub-caliber projectiles, sabot separation is one of the critical aspects. In this work, we focus on the projectiles and the launch package of an electric railgun launch, i.e. on the behavior of the launch-package, when transitioning from the gun barrel to free-flight. This work further addresses the use of a hydrocode for creating numerical models which are capable of predicting the motion and deflection of the sabot parts during their separation from the projectile after exiting the muzzle. An earlier study showed that the air flow around the projectile and the sabot can be modeled with sufficiently high accuracy by means of a simulation code that uses an Eulerian description of the gas flow. Within a time interval of several milliseconds, just the duration that a projectile needs to enter quasi-stationary flight, viscous effects of the air or gas flow have relatively little influence on the sabot discard process. If the Eulerian gas flow is coupled with the Lagrangian structural parts, the mechanical response of the latter to the gas pressure can be complex in terms of deformation and damage, and in that way, can affect the gas flow. In this study, the hydrocode model is applied to a medium caliber launch package concept for accelerating long rod projectiles. The computed results agree well with the corresponding experimental values obtained from a launch package model test in the shock tunnel at Mach 4.5. This demonstrates that the presented hydrocode model can be used for launch package design optimizations with high confidence.