Chapter 19 Instrumented Penetration of Metal Alloys During High-Velocity Impacts P. Jannotti, B. Schuster, R. Doney, T. Walter, and D. Andrews Abstract A methodology is presented for characterizing the failure behavior of metallic targets due to high-velocity and hypervelocity impacts. Time-resolved sub-scale terminal ballistic experiments were performed at approximately 1.2 km/s to assess the feasibility of using high-speed optical imaging, photon Doppler velocimetry, and high-speed 3D digital image correlation for measuring back face deformation. Spherical copper impactors were fired into aluminum alloy targets with thickness equal to one half the impactor diameter. The approach has implications for determining the susceptibility of metallic targets to different failure modes including bulk plastic deformation resulting in tensile failure, cratering, plugging, spallation and adiabatic shear band formation. Results will be used to assist in validation of large-scale computational models used to model ballistic impact. Keywords Impact • Deformation • High-speed imaging • DIC • PDV 19.1 Introduction At present, problems exist both in the efficacy of full-scale experimentation as well as the ability of computational models to accurately capture the complex physics during impact events. This emphasizes the need for high-fidelity, data rich sub-scale experimentation which aims to not only identify and characterize the time-dependent failure of materials, but also to verify and validate the relevant physics for computational models. To this end, real-time experimental analysis is essential to the study of high rate ballistic phenomena. In recent years, popular experimental techniques to capture real-time deformation behavior of ballistic events include high-speed imaging, digital image correlation (DIC) and photon Doppler velocimetry (PDV). Digital image correlation, specifically 3D DIC, enables the user to obtain full-field out-of-plane displacement and velocity fields through pattern-based optical tracking algorithms [1]. Sample preparation consists merely of apply a high contrast pattern to the sample surface. Thus, with the proliferation of ultrahigh speed cameras offering high temporal and spatial resolution as well as relatively long record times (tens to hundreds of microseconds), it is a natural extension for 3D DIC to be used in ballistic testing. Photon Doppler velocimetry, on the other hand, operates on the principle of Doppler shifts, measuring the velocity of a surface with reflected laser light [2]. PDV can sample at the nanosecond level over very long record length (hundreds of microseconds), and is able to measure velocities extending into the tens of km/s range. The use of PDV for rear surface velocity measurements, therefore, offers a wealth of supplementary information to high-speed imaging-based techniques such as accurate time of impact and breakout, evidence of fracture, plugging, or shear banding, and residual projectile velocities. The current study presents time-resolved sub-scale terminal ballistic experiments that will be used to assess the susceptibility of metal alloys to different failure modes. A methodology is presented for analyzing the damage evolution in situ using a combination of high-speed optical imaging, high-speed 3-D digital image correlation (DIC), and photon Doppler velocimetry (PDV). The results of this approach will provide an in-depth examination of operative failure mechanisms and provide model validation for hydrocodes used to simulate the impact events. The intent of this work is to conduct such experiments at ordinance and hypervelocities on a range of metal alloys, but preliminary feasibility studies were performed at 1.2 km/s on aluminum alloy targets. P. Jannotti (*) • B. Schuster • R. Doney • T. Walter • D. Andrews U.S. Army Research Laboratory, Aberdeen Proving Ground, Aberdeen, MD 21005, USA e-mail: Phillip.A.Jannotti.ctr@mail.mil #The Society for Experimental Mechanics, Inc. 2017 D. Casem et al. (eds.), Dynamic Behavior of Materials, Volume 1, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-41132-3_19 139
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