Effect of Contact Geometry on the Slip Amplitude and Contact Pressure in Fretting Fatigue of a Turbine Blade Root

Turbine blades are exposed to mechanical and thermal stresses due to their operation in critical conditions that lead to various damages such as fatigue and wear. These factors reduce the blades life cycle by accelerating the cracking process. In this paper, the effects of three geometric parameters including the contact length, the contact angle, and the surface friction coefficient on relative slip amplitude and contact pressure values in the turbine blade root were investigated using a two-dimensional finite element model. Comparing the results of the analysis with the actual blade damages by use of scanning electron microscopy shows acceptable consistency between predicted damage site and the actual blade damages. The results of the blade analysis indicate that by moving from the top of the contact edge to the bottom, the contact pressure increases gradually and its maximum occurs near the lower edge of the contact. According to the results, the prescribed increments in the coefficient of friction, the contact angle, and the length of contact, respectively decrease the slip amplitude by 26%, 19%, and 10% and also decrease the contact pressures by 35%, 15%, and 5%. In addition, increasing contact angle and coefficient of friction increase the opening region length at the upper edge on both sides of the blade root. While increasing the contact length has no considerable effect on the length of this region.