Fatigue Behavior and Life Prediction of L-PBF Ti64 with Critical Plane Based Small Building Direction Variations...

Area of Science:

• Materials Science
• Mechanical Engineering
• Additive Manufacturing

Background:

• Laser Powder Bed Fusion (L-PBF) enables complex titanium alloy structures.
• Understanding multiaxial low-cycle fatigue (MLCF) is crucial for L-PBF Ti-6Al-4V structural integrity.
• Building direction (BD) significantly impacts material properties and fatigue performance.

Purpose of the Study:

• To systematically investigate the MLCF behavior of L-PBF Ti-6Al-4V across four building directions.
• To characterize cyclic softening and fracture mechanisms under proportional and non-proportional loading.
• To develop and validate accurate fatigue life prediction models accounting for microstructural variations.

Main Methods:

• Strain-controlled MLCF tests were performed on L-PBF Ti-6Al-4V specimens.
• Cyclic softening, fracture surfaces, and microstructural features were analyzed.
• Fatigue life was predicted using analytical (FS, KBMP) and a hybrid VAE-ANN model.

Main Results:

• L-PBF Ti-6Al-4V exhibited distinct three-stage cyclic softening, with non-proportional loading causing predominant softening.
• Defect density and cleavage morphology were identified as key factors influencing fatigue life across different BDs.
• Analytical models showed limitations in capturing BD effects, while the VAE-ANN model achieved high accuracy (within 10% error).

Conclusions:

• Building direction and microstructural characteristics critically govern the MLCF behavior of L-PBF Ti-6Al-4V.
• The hybrid VAE-ANN model, incorporating macro-micro features, offers superior fatigue life prediction for additively manufactured titanium alloys.
• Accurate fatigue life prediction is essential for reliable design and application of L-PBF Ti-6Al-4V components.