TENSILE BEHAVIOUR OF TMCP Q690D HIGH-STRENGTH STRUCTURAL STEEL AT STRAIN RATES FROM 0.00025 TO 760 S-1

Abstract

The application of Q690D high-strength structural steel (HSSS) has been increasing in engineering structures. The lack of knowledge of the strain rate behaviour limits the application to the extreme loading conditions such as blast and impact loadings. This paper presents a series of tensile tests on the dynamic tensile behaviour of Q690D HSSS produced through the thermo-mechanical control process (TMCP). The stress-strain relationships of TMCP Q690D in the strain rate range of 0.00025 to 760 s-1 were measured by using the universal and servo-hydraulic high speed testing machines. The experimental results verified the sensitivity to strain rate of TMCP Q690D and the dynamic increase factor (DIF) for yield stress is identical to that of QT (Quenched and Tempered) S690 HSSS. However, TMCP Q690D behaves in a much different way in the strain hardening stage. The commonly-used Cowper-Symonds model was calibrated for the DIFs of yield stress and ultimate tensile strength. The Johnson-Cook (J-C) model was modified and a new rate-dependent constitutive model was proposed. The proposed model was validated successfully to predict the true stress-strain relationship, providing better prediction results than the modified J-C model.