Predictions have been made of the deformation and failure history of a pipe weldment using a finite element creep continuum damage mechanics model, which incorporates the characteristic material properties of the parent metal, the weld metal and heat-affected zone microstructures of the weldment. It is shown that the computer predictions are in close agreement with the results of large-scale pressure vessel tests, provided that the material characterization is carried out correctly, and that the constitutive equations which control the evolution of creep strain and damage, represent the dominant physical mechanisms present.

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A three-dimensional thermo-mechanical finite element model has been developed and applied to multipass butt-welded mild steel plate and girth butt-welded stainless steel pipe. The simulation results were validated with independently obtained experimental data. The computational model has the potential to be applied to multipass welded complex geometries for residual stress prediction.A full three-dimensional (3D) thermo-mechanical finite element (FE) model has been developed to simulate the step-by-step multipass welding process. Non-linearities associated with welding, such as a moving heat source, material deposition, temperature-dependent material properties, latent heat, and large deformations, were taken into account. The model was applied to multipass butt-welded mild steel plate and girth butt-welded stainless steel pipe for validation. The simulation results were compared with independently obtained experimental data and numerical predictions from two-dimensional (2D) generalized plane strain and axisymmetric models. Good agreements between the 3D predictions and experimental data have been obtained. The computational model has the potential to be applied to multipass welded complex geometries for residual stress prediction.\ud (Professional Engineering Publishing

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The paper examines the possibility of using creep Continuum Damage Mechanics to predict plane strain creep crack growth in compact tension specimens using finite element based numerical methods, coupled with uni-axial and multi-axial stress laboratory creep data, and with mechanisms-based constitutive equations. The predictions of the behaviour of the compact tension specimens made using the single state damage variable equations due to Hayhurst, Dimmer, and Morrison (1984) are shown to be unable to predict that zones of damage do not grow in discrete planar regions as observed in laboratory experiments. To overcome the deficiencies of this approach, new constitutive equations have been developed, which combine the equations of Hayhurst et al. (1984) with those of Cocks and Ashby (1982), to describe the stress-state dependence of the physical mechanisms. The behaviour of the compact tension specimen determined using these new equations predicts lifetimes of the correct order and evolution of damage zones which reflect the growth of discrete cracks as observed experimentally. The paper shows that creep Continuum Damage Mechanics can be used with finite element based numerical procedures to predict creep crack growth, provided that mechanisms-based constitutive equations are used which describe the appropriate stress-state behaviour for each mechanism zone, and that continuity of mechanical properties are achieved across all mechanism boundaries.