LIFE EVALUATION METHOD FOR GAS TURBINE BLADES MADE OF INCONEL718 ALLOY

In turbo jet engines, rotating discs are simultaneously subjected to mechanical and thermal loads. A disc may be under internal pressure due to shrink fit on a shaft, in addition blade effects may be modelled by an external tensile load at the outer radius of the disc when the disc rotates with significant angular velocity while the gases crossing through fins exert a temperature gradient on the disc. Since material behaviour is temperature dependent changes in material properties throughout the blade should be considered. In order to attain a certain and reliable analysis for blade and to derive corresponding stress distribution, solution should consider changes in material specifications caused by temperature. To achieve this goal, an inhomogeneous blade model is considered. Using the variable material properties method stresses are analysed to evaluate the crack initiation and life for the first row blades to reduce the maintenance costs of gas turbines. The temperature and stress analyses are conducted on blades made of INCONEL718 at a temperature of 1300°C. Crack initiation and life evaluation is made based on multi-axial thermo mechanical fatigue (TMF) loading conditions