Virtual melting as a new mechanism of stress relaxation under high strain rate loading

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2012-01-01
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Levitas, Valery
Ravelo, Ramon
Levitas, Valery
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Aerospace Engineering
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Ames Laboratory
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Mechanical Engineering
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Aerospace EngineeringAmes LaboratoryMechanical EngineeringMaterials Science and Engineering
Abstract

Generation and motion of dislocations and twinning are the main mechanisms of plastic deformation. A new mechanism of plastic deformation and stress relaxation at high strain rates (109–1012 s-1) is proposed, under which virtual melting occurs at temperatures much below the melting temperature. Virtual melting is predicted using a developed, advanced thermodynamic approach and confirmed by large-scale molecular dynamics simulations of shockwave propagation and quasi-isentropic compression in both single and defective crystals. The work and energy of nonhydrostatic stresses at the shock front drastically increase the driving force for melting from the uniaxially compressed solid state, reducing the melting temperature by 80% or 4,000 K. After melting, the relaxation of nonhydrostatic stresses leads to an undercooled and unstable liquid, which recrystallizes in picosecond time scales to a hydrostatically loaded crystal. Characteristic parameters for virtual melting are determined from molecular dynamics simulations of Cu shocked/compressed along the and directions and Al shocked/compressed along the direction.

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This article is published as Levitas, Valery I., and Ramon Ravelo. "Virtual melting as a new mechanism of stress relaxation under high strain rate loading." Proceedings of the National Academy of Sciences 109, no. 33 (2012): 13204-13207. 10.1073/pnas.1203285109. Posted with permission.

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