Time-variant fatigue reliability assessment of welded joints based on the PHI2 and response surface methods

A time-variant fatigue reliability assessment model for welded joints subjected to stochastic loading is presented. The PHI2 method, which allows one to solve time-variant problems using time-invariant methods, provides the framework of the model. A sophisticated fatigue crack growth model that is capable of taking the residual stress effect into account is employed to compute crack sizes at different times under stochastic loading. The crack sizes are explicitly represented by response surface models. Limit state functions are formulated based on combined fracture criteria, which consider both brittle and ductile fracture, and the response surface models. The time variant fatigue reliability of a T-plate welded joint with an edge crack located at the weld toe is assessed. It appears that results from the time-invariant fatigue reliability assessment may be too optimistic. The weld induced residual stress effects are considered based on the stress intensity factor due to residual stress. Its effects on the crack size and time-variant fatigue reliability are significant and cannot be ignored.