Fatigue failure analysis of a turbine blade

As a part of aviation, gas turbines need insurances but they actually face to many failures in different stages such as vibration, fatigue, foreign object damage, corrosion, erosion, sulphidation. Turbine blades are the most component that face to failures and affect on the lifetime and the performance of turbines. Several reasons cause failures on blades, several hostile environment factors, the amount of fatigue stress a blade can tolerate, mechanical design problems, temperature and it's cycling, the amplitudes and frequency of vibratory stress, quality control problems within blades or vanes and delivery system problems for the cooling air and turbine section domestic object damage. Although experimental test and analysis of these failures for a real gas turbine in real work condions are very hard and expensive, many research and methods has been improved to analysis fatigure failures and increase turbine life. In This Study, the main goal is analysing HCF and LCF failures in different operate condition for a model based on real designs with Inconel 718 material and investigate failure reasons, to achieve a solution on design of turbine blade with higher life and decreased failure possibility. 3D model of blade and its assembley to disk has been created and using ANSYS software, a finite element model for LCF and HCF analysis prepared. Using this model and discussing on results and comparing to each other, best design parameters would be defined. In General, three loads are acting on turbine blade that cause in high stresses. These loads are hot air pressure, thermal loads caused by hot air, and resulting centrifugal force from rotation of turbine. I get these loads for real gas turbine performance conditions from GasTurb12 software for different conditions. Also to inspect effect of each load on turbine blade life, other loading cases has defined as changing just one load and taking the other two loads constant. Analysis performed in ANSYS and results for these conditions obtained. By studying on results it can be concluded that fir-tree region of blade, which is connection part of blade to disk, is the source of failure caused by high temperature on that part. Blade surface can resist up to 1000C without any fatigue failure, but dovetail of blade can stand up to 500C. In order to improve design life in high loaded conditions with very high temperature, different materials or very efficient cooling system can be used.