Behavior of Thermo-Mechanically Processed AA 6082 Aluminium Alloy Impacted by Conical Projectiles
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RESEARCH PAPER
Behavior of Thermo‑Mechanically Processed AA 6082 Aluminium Alloy Impacted by Conical Projectiles R. Dubey1 · R. Jayaganthan2 · D. Ruan3 · R. Velmurugan1 Received: 23 May 2020 / Accepted: 25 August 2020 © Society for Experimental Mechanics, Inc 2020
Abstract AA 6082-T6 extruded flat bars were reduced to four different thicknesses, viz., 2 mm, 3 mm, 4 mm and 5 mm, using room temperature rolling and subsequently solution treated to obtain homogenized grain structure. These solution treated plates were subjected to cryogenic temperature rolling by immersing in liquid nitrogen before each pass to achieve thickness reductions of 50%, 66.66%, 75% and 80% to 1 mm final thickness. These samples with different cryogenic rolling strains and the same final thickness, clamped on the periphery, were subjected to normal high-speed impact by conical nosed cylindrical projectiles over a velocity range of 50–250 m/s and the projectile impact and residual velocities were recorded. These experimentally measured projectile impact and residual velocities were fitted into Lambert and Jonas model to characterize its parameters. Predicted Lambert and Jonas ballistic limit velocity wise, the samples with 75% reduction performed better when compared with other reductions. The maximum (i.e. 72.5 J) and the minimum (i.e. 15.28 J) energies were dissipated by the sample with 66.66% reduction shot at impact velocity of 216.99 m/s and the sample with 80% reduction impacted at velocity of 243.49 m/s, respectively. The samples with 66.66% reduction demonstrated outstanding energy dissipation, especially at higher impact velocities, in contrast to the samples with other reductions. Keywords AA 6082 · Cryogenic temperature rolling · Normal high speed impact · Conical projectile · Rolling strain · Lambert and jonas model
Introduction The twenty-first century structural materials ought to exhibit high strength-to-weight ratio, higher toughness, optimal hardness, and outstanding fatigue, high speed impact and shock resistance for longer life and reliability during service under dynamic loading and extreme environments [1]. Recent advances in manufacturing techniques to refine the grains to sub-micron levels has further helped overcome the challenges of insufficient strength and propelled the research in understanding the behavior of ultra-fine grained (UFG) materials. Strategies like creating a bi-modal structure, * R. Velmurugan [email protected] 1
Department of Aerospace Engineering, Indian Institute of Technology Madras, Chennai, India
2
Department of Engineering Design, Indian Institute of Technology Madras, Chennai, India
3
Department of Mechanical and Product Design Engineering, Swinburne University of Technology, Melbourne, Australia
consisting of an optimum combination of ductility-enhancing coarse grains and strength-imparting ultra-fine grains, have made it possible to obtain unconventional fusion of properties in metals and alloys [2]. AA 6082 aluminium alloy has been used extensively for various application
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