ESTIMATION OF FATIGUE LIFE AT ELEVATED-TEMPERATURE OF ELECTRON-BEAM WELDMENTS OF ALLOY-718

Axial displacement-controlled fatigue tests were conducted at 600 degree C on smooth solid cylindrical specimens of Alloy 718 with electron beam weldments. By monitoring the diametral strain response of the heat-softened region, relationships between strain amplitude and fatigue life, and between cyclic stress and strain, were obtained. Using the cyclic stress-strain curve of the soft region, the load-controlled fatigue test results corresponded to the axial displacement-controlled test results. Subsequently, a simple model of strain sharing in the weldment was established for cyclic loading in order to estimate the fatigue life. Using the model, the fatigue life of a welded specimen under axial loading was estimated as a function of gage length, considering the effect of gage length on strain concentration in the soft region.