Fatigue Failure from Inner Surfaces of Additive Manufactured Ti-6Al-4V Components

Area of Science:

• Materials Science
• Mechanical Engineering
• Additive Manufacturing

Background:

• Selective laser melting (SLM) enables complex metallic component fabrication.
• Poor surface finish in SLM parts negatively impacts fatigue life.
• Internal channels in components can exacerbate stress concentrations.

Purpose of the Study:

• To investigate the fatigue behavior of Ti-6Al-4V specimens with internal axial channels.
• To compare fatigue performance across different internal channel surface conditions: as-manufactured, drilled, and threaded.
• To evaluate the effectiveness of the Smith-Watson-Topper parameter for fatigue life prediction.

Main Methods:

• Fatigue testing of Ti-6Al-4V specimens produced by SLM.
• Analysis of specimens with internal axial channels (as-manufactured, drilled, threaded) and solid samples.
• Fractographic analysis to determine crack initiation sites and failure mechanisms.
• Application of the Smith-Watson-Topper energy-based parameter for life prediction.

Main Results:

• All specimens with internal channels exhibited lower fatigue performance than solid samples.
• Surface roughness and geometric effects in channels caused stress concentration, reducing fatigue strength.
• Crack initiation predominantly occurred at internal surface defects (unfused particles, lack of fusion).
• Solid samples showed crack initiation from external surface defects.

Conclusions:

• The surface finish and geometry of internal channels in SLM Ti-6Al-4V components significantly reduce fatigue strength.
• The Smith-Watson-Topper parameter is a reliable tool for predicting fatigue life in these conditions.
• Understanding crack initiation sites is crucial for improving the fatigue performance of additively manufactured parts.