Modelling and experimental validation of material deformation at different zones of welded structural-steel under multiaxial loading

The fatigue life assessment of welds represents an engineering challenge regarding material inhomogeneity, welding residual stresses, notch stress effects and multiaxial loading conditions. In a weldment due to the non-uniform heating process the material in the weld metal and adjacent regions may exhibit heterogeneous mechanical properties. This makes the local stress-strain evaluations even more complicated under fatigue loading conditions. Therefore it is essential to characterize the variation of mechanical and particularly cyclic properties of the material in the vicinity of the weld notches. To improve the predictions of fatigue life estimation, numerical modelling techniques are complemented by experimental studies. The present work investigates the effects of weld induced microstructure variations in the multiaxial cyclic properties of the ferritic-pearlitic steels. A numerical model to describe the cyclic plastic deformation behavior of constructional steel S355J2H is established. Two material states present in the vicinity of a weld, the base material and the heat-affected zone (HAZ) are considered. Special attention was given to the non-proportional hardening of the material. Experimental results for both materials are used to calibrate the isotropic and kinematic hardening constants in the Chaboche plasticity model. The calibrated model is applied to multiaxial loading conditions. To account for non-proportional hardening effects, a constitutive motivated parameter by Tanaka is implemented. Therefore, first, the proportional results are reproduced and then the n on-proportionality parameter is incorporated into the isotropic hardening law. The results of the calibration procedure for both proportional and non-proportional multiaxial load paths are discussed regarding its applicability in fatigue analysis and limitations of the model.