Predicting Fatigue Strength in Additively Manufactured Metals: A Novel Minimum Independent Hazard Volume Approach to Size Effects

Additive manufacturing (AM) specimens often exhibit reduced fatigue performance due to inherent defects. This study systematically investigates the combined effects of defect characteristics and microstructural variations on the fatigue strength of AM components. For the first time, a physically meaningful concept termed the “Minimum Independent Hazard Volume” is introduced, and a weakest‐link theory model based on this concept is developed. The proposed model effectively captures the size effect, where larger specimens contain a greater number of fatigue damage sources, and enables the unification of P–S–N curves for specimens of varying sizes. The model's validity is verified through two sets of fatigue test data: one involving AM specimens of different volumes fabricated using identical process parameters, and the other comprising specimens with varying process parameters and volumes. By eliminating the labor‐intensive step of defect size statistical analysis, this model provides a novel approach to studying the size effects of fatigue in additively manufactured metallic materials.