Microstructure-Based Constitutive Model for Yield Strength and Strain Hardening of 5XXX-Series Aluminum Alloys after Non-Isothermal Fire Exposure

Abstract

Aluminum alloys are increasingly being used in a broad spectrum of load-bearing applications such as light rail and marine crafts. Post-fire evaluation of structural integrity and assessment of the need for structural member replacement requires an understanding of the residual (post-fire) mechanical behavior. In this work, models are presented to predict the residual (post-fire) constitutive behavior, including yield strength and strain hardening, at ambient conditions following fire exposure. This model consists of a series of sub-models for (i) microstructural evolution, (ii) residual yield strength, and (iii) residual strain hardening behavior. Kinetics-based (time-temperature dependent) models were implemented to predict microstructural evolution during fire, i.e., recovery and recrystallization for 5xxx-series Al alloys.. The residual yield strength is predicted using individual strengthening contributions and which are function of the microstructural material state. The residual strain hardening behavior is predicted using the Kocks-Mecking-Estrin law modified to account for the additional dislocation storage and dynamic recovery from subgrains. The constitutive model for residual mechanical behavior was bench-marked against AA5083-H116 specimens exposed to conditions resembling those in fire. The residual yield strength and strain hardening models show good agreement with experimental data.