Strain ageing effect on the temperature dependent mechanical properties of partially damaged structural mild-steel induced by high strain rate loading

• Strain ageing effect on mechanical properties of partly damaged steel was studied.
• Damage was induced by high strain rate loading followed by elevated temperatures.
• Two-stage experimental program was designed to incorporate strain ageing effect.
• Results have shown the impact of strain ageing on structural steel behaviour.

This study presents the significant effect of strain ageing on the mechanical response of partially damaged structural steel under extreme loading conditions. Once partial damage occurs in a structure, it takes a while to start the repair process. This lapsed time can substantially affect the strength and ductility of the material. Since the strain ageing effect has not effectively been considered in design guidelines, an understanding of its effect on partly damaged structures is essential. In this paper, a multi-phase loading scenario including high strain rate and quasi-static loadings is applied to the structural mild steel in which partial damage is made to the specimens under high strain rate loading (Phase I). Considering different ageing times ranging from no-age to 7 days, the specimens undergo subsequent quasi-static tensile tests at ambient and elevated temperature (up to 600 °C) until failure (Phase II). Three different damage levels are introduced to examine the damage level effect on strain ageing. It is shown that the variations of ultimate strength and strain values are significantly dependent on ageing time. Presenting a numerical example, the effect of strain ageing on global behaviour of a typical structural component is studied.