Comparison of methods for the determination of fatigue critical flaw size and implementation for probabilistic fatigue assessment

The correct evaluation of the impact of defects in the structural integrity of metal additively manufactured components is a necessary step to be addressed for the broader adoption of the additive manufacturing technology. The effect of flaws on fatigue strength of materials can be evaluated through different theoretical approaches, among which fracture mechanics-based theory was successfully applied in several applications. However, each method presents notable differences which alter the life estimates of parts. Therefore, in this work, the authors compare the fatigue life predicted by four different methods against results from a wide fatigue test campaign on Ti-6Al-4V specimens in different conditions. Then, critical defect size curves, identifying the stress–defect–life relation from each of the analysed model, are established and critically evaluated. Finally, the fatigue strength model based on explicit crack growth analysis, which is the standard assessment method for fracture control, is implemented in ProFACE software. This allows to determine the critical initial flaw size in probabilistic fatigue analyses of components, addressing different geometries and materials.