Simulation and prediction of residual stresses in WAAM-strengthened I-sections

The use of wire arc additive manufacturing (WAAM) as a means of strengthening conventional steelwork is an emerging area of research. An experimental study has revealed that the residual stress distribution in WAAM-strengthened (at the flange tips) I-sections differs significantly from that of a typical hot-rolled I-section, owing to the thermal prestressing arising during WAAM; thus, the establishment of a bespoke residual stress model for WAAM-strengthened I-sections is required. In this paper, 3D thermal-mechanical finite element (FE) modelling is employed to predict the residual stress distributions in WAAM-strengthened I-sections, using two modelling methods - a 3D-transient method and a simplified semi-static method; both modelling methods are shown to provide an accurate representation of experimental observations, with the latter being more computational efficient. Further improvements in computational efficiency, with almost no compromise in accuracy, are achieved through the introduction of a hybrid numerical-analytical approach. The proposed approach uses the simplified semi-static method to simulate the first WAAM layer only and an analytical modification to allow for multi-layer WAAM stiffeners. Using the hybrid approach, a parametric study is performed in which numerical simulations on a total of 524 benchmark members with varying geometric properties covering a wide range of UK and European I-sections are carried out. Based on the obtained results, predictive expressions for the residual stress distributions in WAAM-strengthened I-sections are developed; the predicted residual stress patterns are shown to be in good agreement with both experimental and numerical results. Use of these expressions is recommended to determine the pattern and magnitude of residual stresses in WAAM-strengthened I-sections for the purposes of numerical simulations and the development of structural design provisions.