Fatigue crack propagation life prediction using linear elastic fracture mechanics is usually based on the assumption that applied stress is perpendicular to initial cracks. Therefore, its application for combined normal and shear stresses is somewhat limited. In this study, fatigue crack propagation life prediction of weld joints under the combined stresses is discussed. Based on the concept of the strain energy release rate, the modified Paris' equation expressed by equivalent stress intensity factor is proposed. Fatigue crack propagation lives of butt welded joints containing an inclined lack-of-penetration and non-load-carrying fillet welded joints with inclined ribs are calculated, and they are compared with the test results.
