Monday, 11 October 2004 - 9:15 AM

This presentation is part of : Graduate Student Competition

Sublimation inside of elastoplastic material

Nataliya Altukhova and Valery I. Levitas. Texas Tech University, 7th & Boston, ME dept. TTU, Lubbock, TX 79409-1021

During material loading, high temperature can be induced in local spots inside the material, e.g. due to shear bending. High temperature can cause sublimation, i.e. phase transformation solid-gas. Sublimation on hot spots followed by chemical reactions in gas phase is one of the mechanisms of ignition of various explosives. In the paper, thermodynamic and kinetic approaches for sublimation inside of elastoplastic material are developed. Sublimation is considered as a transformation of small volume of solid into gas. Using continuum thermodynamics, a driving force for sublimation, X, is derived. A thermodynamically equilibrium relationship between pressure and temperature were obtained from the condition X=0. Nucleation time is determined by Arrhenius-type kinetic equation with the derived expression for activation energy. Kinetic criterion for thermally activated sublimation is formulated. The problem of nucleation of spherical gas bulb inside the spherical elastoplastic material is solved analytically for finite strains using known solution for deformation of elastoplastic sphere by internal and external pressure. Thermodynamically equilibrium and kinetically admissible relationships between sublimation pressure and temperature were obtained. These relationships were compared with those for sublimation from external surface (pressure is constant) and sublimation in rigid solid (volume is constant). Alternative scenario, based on void nucleation (cavitation) followed by sublimation from the void surface is considered as well. Results are specified for sublimation in HMX energetic crystal.

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