Shawoon K. Roy

Study of hypervelocity projectile impact on thick metal plates

Hypervelocity impacts generate extreme pressure and shock waves in impacted targets that undergo severe localized deformation within a few microseconds. These impact experiments pose unique challenges in terms of obtaining accurate measurements. Similarly, simulating these experiments is not straightforward. This study proposed an approach to experimentally measure the velocity of the back surface of an A36 steel plate impacted by a projectile. All experiments used a combination of a two-stage light-gas gun and the photonic Doppler velocimetry (PDV) technique. The experimental data were used to benchmark and verify computational studies. Two different finite-element methods were used to simulate the experiments: Lagrangian-based smooth particle hydrodynamics (SPH) and Eulerian-based hydrocode. Both codes used the Johnson-Cook material model and the Mie-Gruneisen equation of state. Experiments and simulations were compared based on the physical damage area and the back surface velocity. The results of this study showed that the proposed simulation approaches could be used to reduce the need for expensive experiments.

Comparison of Failure Mechanisms Due to Shock Propagation in Forged, Layered, and Additive Manufactured Titanium Alloy

The objective of this paper is to propose experimental techniques for studying the behavior of titanium alloy, Ti-6Al-4 V (Grade 5), under shock loading. Single-layer and multi-layered stacks of forged titanium, and additive manufactured (AM) titanium plates were considered. In these experiments, target materials were subjected to ballistic impact using a two-stage light gas gun. A Photonic Doppler Velocimetry (PDV) diagnostics system was used to measure free-surface velocity on the back of each target. The experimental measurements were used to describe the behavior of these materials under shock loading. In addition to velocity measurements, physical damage and spall crack formation were monitored.

Use of a Multiplexed Photonic Doppler Velocimetry (MPDV) System to Study Plastic Deformation of Metallic Steel Plates in High Velocity Impact

High-velocity impact experiments with a gas gun pose unique challenges, in terms of experimental setup and computational simulation, since the projectile-target interaction creates extreme pressure and temperature within few micro seconds. The objective of this study is to accurately measure the plastic deformation of plates under projectile impact that does not lead to full penetration. In this work, free surface velocities at the back side of target plates are measured using the newly developed Multiplexed Photonic Doppler Velocimetry (MPDV) system, which is an interferometric fiber-optic technique which can measure velocity from the Doppler shift of the light reflected from the moving back surface of the target. The MPDV system allows measurements of velocity from different locations on the target plate using multiple optical fiber probes oriented in specific directions and patterns. Data are reduced using a Fast Fourier transformation (FFT) technique to obtain the free surface velocity profiles. These velocity profiles can present insights into the dynamic behavior of impacted materials under shock loading conditions.

PARAMETRIC SENSITIVITY COMPARISON OF SIMULATION MODELS FOR FLYER PLATE IMPACT EXPERIMENTS

This article presents a study of the sensitivities of different parameters that affect the accuracy of simulating flyer plate impact experiments. Two approaches are explored: the CTH hydrodynamic and the LS-DYNA smoothed particle hydrodynamic (SPH) codes. Simulations using these two methods are compared to experimental data from a single-stage gas gun experiment in which a copper flyer plate impacted another copper target plate. The experiment was designed to cause spall in the target plate. The numerical simulations are conducted using these combined physics models: the Mie– Gruneisen equation of state, the Johnson–Cook compressive strength model, and spall rupture. Effects of artificial viscosity, spall strength, and computational cell size are studied and discussed with the objective of improving the accuracy of these simulations. The results are verified by applying the proposed simulation approach to other flyer plate experiments.