Fatigue life prediction of TC17 titanium alloy based on micro scratch

Micro scratch with depth and width of micron expresses a significant influence on fatigue life. However, little literature is available on modelling the effect of micro scratch on the fatigue life of TC17 titanium alloy. In this paper, the geometric characteristics of micro scratch, especially depth and width, were obsevered and measured. Then, fatigue experiment was conducted to obtain the corresponding fatigue test data. Result shows the presence of micro scratches dramatically reduced the fatigue life from very high cycle fatigue (VHCF) to the high cycle fatigue (HCF) regime. According to the geometrical characteristics of micro scratch, two principles of no obvious influence of scratch direction and length on fatigue life was proposed based on Murakami theory. A new parameter area. is proposed to describe fatigue damage quantitatively caused by micro scratches, which is defined as the square root of triangle area of scratch section. An HCF life model of TC17 with the consideration of micro scratches is established by the combined application of area. and Paris formula. The validity of the model is confirmed by a good agreement between predicted and experimental results.