ON STABILITY OF VISCOPLASTIC SYSTEMS WITH THERMOMECHANICAL COUPLING.
BROWN UNIV PROVIDENCE R I DIV OF ENGINEERING
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The stability of equilibrium configurations of thermo -mechanically coupled systems in the plastic and the viscoplastic range is examined through simple examples and by dimensional analysis. A uniform fully-insulated thin-walled tube twisted into the inelastic range is studied first. The material is idealized as linear work-hardening viscoplastic with a current yield stress which decreases linearly with increase in temperature. Any annealing or age-hardening or similar influence of time at temperature is supposed negligible. A local stability criterion beta 1 governs, where beta is the ratio of the heat stored in the material to the heat generated by inelastic deformation with a given temperature rise. Neither viscosity nor heat conduction enters into the stability or instability of this homogeneous system. They both play a role in successive modifications of the simple model which demonstrate the stabilizing effect of heat transfer to the surroundings and of the heat capacity in regions of material below yield. Author