Fatigue life prediction for PBF-LB Ti6A14V with as-built surface under nonproportional loads using an incremental fatigue damage model

• Published in: International journal of fatigue 2025-04, Vol.193, p.108777, Article 108777
• Main Authors: Lindström, Stefan B., Moverare, Johan, Franke, Manja, Persson, Johan, Leidermark, Daniel, Thore, Carl-Johan, Lindström, Thomas, Kapidžić, Zlatan
• Format: Article
• Language: English
• Subjects: High-cycle fatigue; Incremental fatigue damage model; Powder bed fusion with laser beam; Tension-torsion tests; Ti6Al4V
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2024.108777

This study evaluates the Ottosen–Stenström–Ristinmaa (OSR) incremental fatigue damage model for predicting fatigue life in powder bed fusion with laser beam (PBF-LB) Ti6Al4V notched specimens. To fit the OSR model, we conduct constant-amplitude tension-compression fatigue tests on PBF-LB Ti6Al4V specimens with as-built surface. Our results highlight a relatively low scatter in fatigue life data for PBF-LB Ti6Al4V across different studies, a critical factor for reliable design against fatigue failure. The study suggests that the stress gradient effect is influenced by the as-built surface, which carries load differently from the target build geometry due to surface undulations. The OSR model effectively captures the characteristics of Wöhler curves for various notch geometries and stress ratios. We validate the OSR model with out-of-phase tension-torsion tests, demonstrating that it provides safe fatigue life predictions for nonproportional loads. Overall, our findings show that the OSR model offers conservative fatigue life predictions for PBF-LB Ti6Al4V, underscoring its practical utility and reinforcing the suitability of PBF-LB Ti6Al4V for aircraft applications. •Time-domain model predicts fatigue life for AM Ti6Al4V under nonproportional loads.•Fatigue life scatter for PBF-LB Ti6Al4V is surprisingly low across studies.•The stress gradient effect is influenced by surface roughness in as-built PBF-LB.•Conservative fatigue predictions observed for critical load conditions.•PBF-LB Ti6Al4V shows potential for reliable design in demanding aircraft applications.