Failure estimation of TIG butt-welded Inco718 sheets at 620 °C under creep and plasticity conditions

This paper describes the creep behaviour of plain, notched and welded specimens machined from Inco718 sheet material. The Inco718 welded sheets experience out of plane distortion due to the welding process and these sheets also have weld beads with sharp fillet radii. Both the out of plane distortion and the fillet radii result in high stress concentrations and local plastic deformations which can significantly affect the failure life of the sheets, at high temperature, under creep conditions. Experimental creep testing using plain, notched and welded specimens was carried out at 620 °C. From the test data, the plasticity behaviour and the creep and damage constitutive equations were obtained for the material. On this basis, failure predictions of the welded sheets, based on continuum damage mechanics modelling, were conducted, using the finite element method. The results obtained are compared with the corresponding experimental data and the applicability of the method for predicting failure lives is discussed.