Effect of strain ageing on the mechanical properties of partially damaged structural mild steel

ABSTRACT
This paper addresses the strain ageing effects on the mechanical properties of the partially damaged structural mild steel. Since repairing partly damaged structures may not occur immediately, the strain ageing effect can significantly influence the structural behaviour. The changes due to this effect have not so far been considered in the civil engineering design guidelines. In order to investigate strain ageing effects, two-stage experimental tests are carried out on the mild-steel specimens. In the first stage, partial damage is made using quasi-static loading. During the second stage, the strength and ductility of the specimens are examined after 2 and 7 days ‘ageing’ at room temperature and the results are compared with the corresponding no-age samples. The microstructure of the specimens is examined using scanning electron microscopy (SEM). To illustrate the effect of strain ageing on the global behaviour of steel structures, a numerical example is provided in which strain ageing impacts on loading capacity and deflection of a steel beam. Finally, the stress–strain relation of partially damaged mild-steel material incorporating strain ageing effects is expressed by calibrating the parameters of Ramberg–Osgood model.