Effect of notch geometry on the fatigue strength and critical distance of TC4 titanium alloy

Abstract

Studying the effect of different geometric features of machined notch on the fatigue strength and critical distance has an important guiding role to understand the critical distance size effect and to predict the HCF strength of turbine engine fan blades after FOD. Systematically experimental investigations of geometrical characteristic effects on the 106 cycle fatigue strength and critical distance for TC4 machined notched plates at stress ratios of R = 0.1 have been conducted. 123 specimens, including unnotched plates and three different types of notched plates (V-notches, U-notches and C-notches) with various notch root radii, depths and angles have been considered. The results indicate that the notch with small radius can significantly lead to high stress concentration and greatly reduce the HCF strength, while the notch angle and notch depth can affect the HCF strength to a certain extent. The K t related model does not apply to describe the critical distance size effect perfectly. The critical distance has linear relationship with the notch root radius but no significant correction with the notch depth or notch angle. The findings of this study are beneficial for the size effect modeling and later fatigue strength evaluating of TC4 notched components.