A simple fracture mechanics estimation of the fatigue endurance of welded joints

The use of fracture mechanics based methodologies to assess the influence of defects on welded components has become increasingly important for industrial applications and design, in the last decades. However, there are still objections against these approaches due to their complexity and the consequent need of qualified personnel with certain level of knowledge of fracture mechanics. Therefore, development of simplified methods to evaluate severity of defects can be valuable for practical purposes. In the present work, a manageable expression is proposed to calculate the applied stress intensity factor for crack growth, which is proportional to the square root of crack length and the stress concentration factor at the location of the crack in the un-cracked body. The latter was obtained with numerical simulation of transversely loaded butt, T and cruciform joints. By means of the resistance curve method that accounts for short crack behaviour, these results can be compared with threshold for crack propagation to estimate the fatigue resistance of welded joints. Besides, a simple expression was derived to estimate the fatigue endurance, which can be used to understand and analyse in a simplified manner the influence of the main geometrical and mechanical parameters, like weld geometry, residual stresses and size of defects, among others. Estimations were compared with experimental results from literature for different weld configurations, and they proved to be conservative. Methodology is valid for toe cracks in as-welded joints.