Hassan Alizadeh

An eigenstrain-based model for residual stress arising from transient local surface heating

We present a model for approximating residual stresses arising from thermally induced plasticity and apply it to a simple two-dimensional (plane strain) test problem of transient heating. The model uses stress fields derived from simple eigenstrains to perturb an initially elastic-only solution in a way that mimics plastic flow. The plane strain condition of the test problem gives rise to plastic strains in the out-of-plane direction, owing to constraints on thermal expansion. However, the model is able to cope with the challenges this poses and also encapsulates the time-dependent nature of the problem. We show that the model agrees well with finite-element simulations under moderate strength heat sources provided that appropriate plastic flow rules are used. There exists sufficient generality in the model to allow its extension to more realistic scenarios.

Measurement and Prediction of the Residual Stress Field in an Autogenously Welded Stainless Steel Plate

There has been a concerted effort over recent years to develop and refine finite element models of welds in order to predict residual stresses. These residual stresses are required to ever improved accuracies in order to provide continued confidence in the safe operation of ageing plant. Not only have computing hardware and software developed at a rapid rate, but guidelines for weld modelling ‘best practice’ have started to be documented. In order to validate and verify weld modelling procedures, test specimens are required which may be subjected to a suite of residual stress measurement techniques in order to allow comparison and ‘benchmarking’ of the numerical predictions. An abundance of such test specimens have been developed over the last few years. These are typically studied via large multi-national ‘round robins’ and results used to fine tune methodologies. A specific example is the NeT ‘bead on plate’ specimen [1, 2] which considered a single weld bead on an austenitic stainless steel plate. Whilst the major thrust worldwide now is to fabricate and study test specimens more representative of real plant, by considering larger specimens, many weld passes, different materials (including ferritic steels and their associated phase change during welding), the research presented in this paper considers an even simpler test specimen. Thus, an autogenous (no filler material) weld on a stainless steel plate is considered. There were two principal motivations for this work. Firstly, numerical and experimental results were required to validate analytical models of welding induced residual stresses. These analytical models [3] are currently under development but, to date, have been formulated only for parent material. Secondly, the lessons learned on weld modelling from previous studies were desired to be tested on the simplest test specimen available.© 2008 ASME

Early Developments for a Semi-Analytical Model of Weld Induced Residual Stress

The generation of plastic slip and residual stress by thermal processes is particularly difficult to understand and simulate. Modelling such problems is computationally expensive when approached numerically and extremely complex to approach analytically. ‘Semi-analytical’ models, in which analytical thermoelastic solutions are combined with approximate models of plasticity, offer a way to bridge this gap and have the potential to allow the rapid testing of parameter sensitivities before one launches a time-consuming full numerical model. However the construction of such models within such a thermal framework poses its own problems. An initial requirement for any such semi-analytical model is a complete solution to the elastic only response of the material to the given loading process. In this paper we focus on the formulation of such a solution for the simplest case relevant to welding or similar thermal processing. We verify the solution developed against finite element predictions and then further investigate it. In doing so we explain how the nature of this solution, especially its predicted yielding behaviour, has ramifications for the successful creation of a full semi-analytical solution.Copyright