Probabilistic fatigue limit estimation in welded joints containing defects using the cyclic R-curve analysis and the Peak Stress Method

• PSM and cyclic R curve are coupled to estimate the fatigue limit of welded joints. • The fatigue limit is estimated from the uncracked local stress field. • Validated for weld toe angles 135°, 150°, and 180° against literature datasets. • Defects reduce fatigue limit, especially for larger defects and wider opening angle. The constant amplitude fatigue limit (CAFL) of welded joints is governed by the threshold behaviour of short cracks, which initiate at the critical point (weld toe or weld root) and become non-propagating beyond a certain distance. This investigation proposes a procedure for estimating the CAFL of welded joints by combining the cyclic R-curve analysis, which describes the fatigue crack propagation threshold of short cracks, with the Peak Stress Method (PSM), which is an engineering approach for analysing readily the severity of the local stress field in the uncracked, sharply notched weld root or weld toe. Within this framework and focussing on the weld toe, the fatigue limit is identified by a threshold value of the local stress field of the uncracked configuration, while implicitly incorporating the crack arrest condition dictated by the cyclic R-curve. A Monte Carlo analysis was performed to account for the intrinsic variability of the cyclic R-curve parameters, considering different probability distributions. The proposed procedure extends the PSM design framework by introducing the CAFL on the existing PSM-based design scatter band. The resulting CAFL was validated against several experimental datasets, covering welded joints with different weld toe opening angles. Overall, a good agreement was found between theoretical estimations and experimental results. The model was finally extended to investigate the role of defects at the critical points (e.g. undercuts at the weld toe), demonstrating quantitatively that such defects reduce the CAFL, particularly for larger defect sizes and wider weld toe opening angles.