On Void Growth in Elastic-Nonlinear Viscous Solids Under Creep and Cyclic Creep Conditions

Abstract

The growth of initially spherical periodic grain boundary voids in an elastic-nonlinear viscous material is investigated. Large geometry changes are taken into account to correctly capture the trend of void growth rate and evolution of void shape. To this end, an axisymmetric unit cell model of the damaged material is considered. The temporal characteristics of the void growth rate and shape changes and void interaction effects were determined for several triaxial stress states, under constant stress conditions. The results are compared with existing approximate analytical models for void growth rate in a purely nonlinear viscous solid. The finite element calculations indicate that while the effect of elasticity is minimal in determining the transient time for void growth, the growth rates after the initial transient may be more rapid in elastic-nonlinear viscous materials compared with the rates for purely nonlinear viscous materials, especially so under high triaxial stress states. In addition, the approximate analytical expression for void growth rates significantly under predicts the rates for high triaxial stress states and predicts a wrong trend for low triaxial stress states. Calculations of void growth under balanced strain cycling conditions are also performed. The results indicate that void growth can occur, consistent with experimental observations under balanced cycling loading conditions, provided nonlinear shape changes are taken into account. In addition, the analyses show that the cavity growth rate is constant under balanced cyclic loading conditions. This observation is in agreement with the experimental findings of Barker and Weertman (1990, Scr. Metal. Mater. 24, pp. 227–232). That material elasticity does not play any role in void growth or shrinkage under balanced cyclic creep conditions is also clearly demonstrated by the results. [S0094-4289(00)00803-3]