Residual stress analysis and finite element modelling of repair-welded titanium sheets

An innovative FE modelling approach has been tested to investigate the effects of weld repair thin sheets of titanium alloy, taking into account pre-existing stress field in the components. In the case study analysed, the residual stress fields due to the original welds are introduced by means of a preliminary sequentially-coupled thermo-mechanical analysis and considered as pre-existing stress in the sheets for the subsequent weld simulation. Comparisons are presented between residual stress predictions and experimental measurements available from the literature with the aim of validating the numerical procedure. As a destructive sectioning technique was used in the reference experimental measurements, an investigation is also presented on the use of the element deactivation strategy when adopted to simulate material removal. Although the numerical tool is an approximate approach to simulate the actual material removal, the strategy appears to compute a physical strain relaxation and stress redistribution in the remaining part of the component. The weld repair modelling strategy and the element deactivation tool adopted to simulate the residual stress measurement technique are shown to predict residual stress trends which are very well correlated with experimental findings from the literature

On a Model for the Prediction of the Friction Coefficient in Mixed Lubrication Based on a Load-Sharing Concept with Measured Surface Roughness

A new model was developed for the simulation of the friction coefficient in lubricated sliding line contacts. A half-space-based contact algorithm was linked with a numerical elasto-hydrodynamic lubrication solver using the load-sharing concept. The model was compared with an existing asperity-based friction model for a set of theoretical simulations. Depending on the load and surface roughness, the difference in friction varied up to 32 %. The numerical lubrication model makes it possible to also calculate lightly loaded contacts and can easily be extended to solve transient problems. Experimental validation was performed by measuring the friction coefficient as a function of sliding velocity for the stationary case

Computation of residual stresses for a repair weld case

The target of EU FP7 STYLE project (Structural integrity for lifetime management - non-RPV component) was to improve and unify the methods of a structural integrity assessment in the ageing and lifetime management of reactor coolant pressure boundary components. One of the mock-ups in the project was manufactures from two pipes welded together. After completion of the girth weld, a deep weld repair was inserted into the girth weld. As a part of the work, roundrobin finite element computations were performed to determine residual stresses after repair welding and the computational results were compared to the deep hole drilling measurements. In this paper, the details and recomputed results of one of the analyses is presented. A part of the input data was generated with in-house codes. Sequential thermal and mechanical analyses were performed with a small strain and displacement formulation. The comparison of computed and measured temperatures and stresses shows good agreement. The computed hoop stress at the repair mid-length was higher than the axial stress. Both stresses were tensile through the wall thickness. Confidence in the results was also gained as the results were compared to those presented in the literature for a repair welding case