Comparison of the fatigue life of pure titanium and titanium alloy clasps manufactured by laser powder bed fusion and its prediction before manufacturing.

PURPOSE: In this study, the fatigue properties of additively manufactured titanium clasps were compared with those of commercially pure titanium (CPTi) and Ti-6Al-4V (Ti64), manufactured using laser powder-bed fusion. METHODS: Fourteen specimens of each material were tested under the cyclic condition at 1 Hz with applied maximum strokes ranging from 0.2 to 0.5 mm, using a small stroke fatigue testing machine. A numerical approach using finite element analysis (FEA) was also developed to predict the fatigue life of the clasps. RESULTS: The results showed that although no significant differences were observed between the two materials when a stroke larger than 0.35 mm was applied, CPTi had a better fatigue life under a stroke smaller than 0.33 mm. The distributions of the maximum principal stress in the FEA and the fractured position in the experiment were in good agreement. CONCLUSIONS: Using a design of the clasp of the present study, the advantage of the CPTi clasp in its fatigue life under a stroke smaller than 0.33 mm was revealed experimentally. Furthermore, the numerical approach using FEA employing calibrated parameters for the Smith-Watson-Topper method are presented. Under the limitations of the aforementioned clasp design, the establishment of a numerical method enabled us to predict the fatigue life and ensure the quality of the design phase before manufacturing.

Probabilistic finite element analysis of fatigue life of additively manufactured clasp.

The present study was aimed to develop a probabilistic finite element method (FEM) that predicts the variability in the fatigue life of additively manufactured clasp so that it can be used as a virtual test in the design phase before manufacturing. Titanium alloy (Ti-6Al-4V) clasp with integrated chucking part, which was designed for experimental fatigue test to validate the computational method, was investigated. To predict the lower bound, an initial spherical defect was assumed in the region where stress concentration was predicted. The Smith-Watson-Topper (SWT) method, Bäumel & Seeger rule, elasto-plastic FEM, and zooming FEM were used. The influence of assumed initial defect on the fatigue life was significant, and the large variability in the fatigue life was predicted. This study demonstrated that the proposed practical computational method can simulate the large variability in the fatigue life of titanium alloy clasp, which is useful in its design before manufacturing.