A MULTIPLE CRACK MODEL FOR FATIGUE IN WELDED-JOINTS

Several linear elastic fracture mechanics (LEFM) models have been deve loped to simulate the fatigue performance of welded joints, particular ly for offshore structures. Such models are used to estimate residual life when cracks are discovered in service. These models are also used to interpret available experimental results and may eventually be use d in design. A key element to the success of such models is the realis tic modelling of fatigue crack shape development. In all fatigue testi ng of welded T-plate, pipe-plate and tubular joints in the Canadian Of fshore Research Programme, care was taken to monitor crack shape devel opment using beach marks and potential-drop techniques. Crack shape de velopment was significantly influenced by specimen thickness, stress d istribution and environment. A fatigue model is proposed which explici tly models the growth and coalescence of multiple semi-elliptic fatigu e cracks. Such a model has the potential of modelling geometry and env ironmental effects through their influence on crack shape development. The basics of this model, including coalescence and the calculation o f stress intensity factors, are discussed. Verification studies involv ing both T-plate and pipe-plate specimen geometries are presented.