Hysteresis behavior of EQ56 high strength steel: Experimental tests and FE simulation

The probability of offshore platforms suffering to extreme cyclic loads, such as storm surges and typhoons, in-creases highly at deep sea. It is essential to achieve the hysteresis behavior of steel material for evaluating the dynamic response of offshore platform under cyclic load. A total of 18 coupons are fabricated from the EQ56 high strength steel (HSS) plate to investigate the monotonic and cyclic behaviors. Loading protocols include mono-tonic tension, constant amplitude and changing amplitude strain-controlled cyclic loadings. It is revealed that the visco-plastic behavior of EQ56 HSS is insignificant under the monotonic tension at room temperature. The EQ56 HSS presents obvious Bauschinger effect, non-masing rule, stress hardening/softening behavior and strain history memory effect under strain-controlled cyclic loading. The prior loading history at low strain-amplitude levels has little effect on the saturation stress of EQ56 HSS while stress hardening can be reactivated to a new saturation level when the applied strain-amplitude is increased. The monotonic and the cyclic hysteresis curves of EQ56 HSS were compared, and hysteretic skeleton curves are fitted using the Ramberg-Osgood model. The essential parameters of the Chaboche combined hardening model are calibrated to describe the cyclic behavior of EQ56 HSS. The comparison between FE simulation and test results demonstrates that this model cannot characterize effectively the hysteretic behavior of EQ56 HSS because the strain history memory effect and coupled behavior of cyclic stress softening and hardening are ignored in its constitutive equation.