High temperature life prediction of a welded IN718 component

Life predictions from a case study of a welded feature in a generic spoke structure, determined using three-dimensional quasi-static elastic-plastic and creep finite element analyses, are demonstrated. The complete structure consists of multiple Inconel 718 (IN718) TIG-welded features; the welds exhibit noticeably depleted mechanical properties so a multimaterial analysis is necessary for accurate predictions. The effect the welds have on the life is investigated for both constant (creep) and cyclic loading (creep-fatigue) conditions at 620°C. Creep damage and Smith, Watson and Topper (SWT) strain parameter lifing methods are used, based upon material properties determined using uniaxial test data. The lower fatigue properties of the welded IN718 material at high temperature had a negative effect on the fatigue life of the structure. The effect of the weld on the life under constant loading at high temperature was found to be more difficult to evaluate due to significant stress relaxation.