Constitutive Modelling of Ductile Metals at High Temperature

Abstract

Constitutive behaviour of ductile metals subjected to thermo-mechanical loads associated with a fire condition as well as small-to-medium rate mechanical loads is discussed in this paper. Effective analysis and design of structures in fire require material models that are valid over a wide range of stresses, strain rates, loading and unloading cycles and temperatures. Thermal loading of metals results in a slow, creep-dominated behaviour, which can lead to local or global component failures and progressive collapse. The collapse mechanism for structures and their components, once initiated, occurs at much higher strain rates than creep. A comprehensive modelling framework that allows simulation of large-scale metal structures subjected to a wide range of stresses, strain rates and temperatures is presented. An advanced viscoplastic constitutive model is developed based on micromechanical material failure mechanisms and experimentally observed time- and temperaturedependent material behaviour. This model (WAifire) allows bridging the time-scale gap between creep-dominated behaviour and resulting thermo-mechanical stiffness and strength degradation on the one hand, and the high strain rate deformation and fracture caused by structural collapse on the other hand.