Fatigue life assessment of welded joints based on the decomposition of the structural hot spot stress

The methodology for fatigue life prediction of welded joints was evaluated using the hot spot stress concept and considering the fatigue crack initiation and crack propagation stages. The research carried out in this project was to validate a method for the determination of stress concentrations and stress distributions in weldments using the shell finite element stress data. A procedure was also developed to estimate the peak stress at the weld toe from experimental stress measurements in the weld toe neighborhood.; The first part of the research dealt with the fatigue analysis of a square tube-on-plate welded joint having fillet weld. The shell finite element analysis procedure proposed earlier, and called as the GY2 model was used in the analysis. In order to validated the procedure the stresses obtained from the GY2 shell finite element model were compared with the stress data obtained from 3D finite element model of the same object. The stress peak and the stress distribution at the critical cross section based on the GY2 stress data were subsequently used to determine the expected fatigue life. The prediction of the total fatigue life required the analysis of the fatigue crack initiation and crack propagation period. The fatigue crack initiation life was estimated using the strain-life method, and the crack propagation life was predicted using the fracture mechanics approach. In order to compare predicted lives with the experimental data, several series of tests were carried out at the John Deere Company laboratory.; In the second part of the project, a procedure for obtaining the peak stress and the through thickness stress distribution was developed based on the stresses measured experimentally in the weld toe region. The stresses found experimentally were used to estimate the hot spot stress and subsequently the peak stress at the weld toe necessary for the fatigue analysis. Various procedures where developed for; T-joints, cruciform joints and lap joints, and for the gusset joint configuration. Recommendations were formulated concerning the exact locations of strain gauges.