Strain hardening exponent and strain at maximum stress: Steel rebar case

Abstract

The typical distribution of steel used in developed countries, according to World Steel Association, attributes approximately 35% of total steel production in the world to the construction sector. Rebar steel consumption constitutes a significant proportion of that figure. More in-depth knowledge regarding the behaviour of steels used in the production of rebar would be advantageous. It has been shown that elasto-plastic behaviour greatly affects the behaviour of steel under seismic action. In particular, the engineering strain at maximum engineering stress, Agt, is gaining importance as the key ductility parameter in the latest standards. Several authors have linked the value of Agt to the Hollomon strain-hardening exponent, n. Three materials have been tensile tested at room temperature, namely TEMPCORE® carbon steel, an austenitic, and duplex steel. In this paper, it is shown that such a link is only valid when the local n value is computed at A → Agt (εz → εgt in true values). In accordance with the metallographic structure of rebar, the contrasting behaviour of the Hollomon strain-hardening exponent n versus εz is described.