Mechanical properties and constitutive model of WAAM high performance steel circular tubes at post-fire conditions

In this study, 44 coupon specimens cut from the Wire Arc Additive Manufacturing (WAAM) tubes were heated to different high temperature levels and then cooled down to ambient temperature inside the furnace. Subsequently, the coupon specimens were tested to evaluate their mechanical properties after being subjected to elevated temperatures in the range of 300°C to 1000°C. The WAAM tubes were fabricated by two stock wires, the high strength steel ER120 and stainless steel ER316. The fabricated tubes have nominal thickness of 2.5 mm and 4.0 mm. The coupon specimens were heated in an electric furnace to six different nominal peak temperatures, with the highest temperature of 1000 °C. Tensile coupon tests were conducted to investigate the post-fire residual mechanical properties associated with the stress-strain curves, such as Young’s modulus, 0.2% proof stress, ultimate stress, Ramberg-Osgood parameter, ultimate strain and fracture strain. The retention factors of the mechanical properties under post-fire conditions were obtained and investigated. The retention factors were compared with the predictive curves from the literature that were based on conventional high strength steel and stainless steel specimens. The findings indicated that current curves overly provided conservative predictions to those of WAAM specimens. New curves were proposed for the retention factors of mechanical properties of WAAM high performance steel (high strength steel and stainless steel) under post-fire conditions. It is shown that the proposed retention factors generally provide better predictions than those from the current curves. In addition, a constitutive model was proposed to predict the stress-strain curves of WAAM high performance steel at ambient and post-fire conditions. • WAAM high strength steel and stainless steel circular tubes fabricated. • Mechanical properties of WAAM tubes at post-fire conditions tested. • Retention factors for post-fire mechanical properties obtained. • Curves for predicting WAAM post-fire mechanical properties proposed. • Two-stage model for stress-strain curves of WAAM tubes at post-fire proposed.