Optimisation of Weld Modelling Techniques: Bead-on-Plate Analysis

Finite element studies have been carried out simulating 3-dimensional deposition of weld metal on a flat plate. The purpose of this work is to further understand and develop the modelling requirements in order to accurately predict post weld residual stresses when compared to residual stress measurements. A single bead on plate specimen has been chosen as it has similar characteristics to those occurring in a repair weld which is of engineering interest. This analysis makes use of detailed fabrication records such as thermocouples, recorded heat inputs and etched macrographs which detail the fusion boundary profile. Analysis of the macrographs indicate a reduced weld penetration towards the end of the weld bead and especially along the centre-line of the bead where a “double-lobed” appearance was noted when viewed on a plane perpendicular to the bead. At the start position, a deeper fusion boundary was observed relative to the majority of the weld bead. The aim of this piece of work was to match the observed and predicted fusion boundaries and to analyse the influence on the predicted residual stresses when compared to a constant fusion boundary, along the length of the bead, as modelled in earlier analysis of the bead-on-plate. Two mechanical simulations were conducted based upon the matched fusion boundary thermal solution. These mechanical simulations utilised two hardening models, both of which are based on a non-linear kinematic hardening model but derived from different test data. A baseline kinematic hardening model has been used that is derived from monotonic and single pass weld bead specimens. A mixed hardening model has also been used which has been derived from both monotonic and cyclic test data. Furthermore this analysis takes advantage of some new features to weld modelling. In particular these include the Dynamic Fusion Boundary (DFB) approach where material properties are assigned to elements according to their temperature history.