Mechanism and modeling of fatigue crack initiation and propagation in the directionally solidified CM186 LC blade of a gas turbine engine

Abstract

First-stage blades of gas turbines are elements positioned after the combustion chamber and are responsible for extracting energy from high temperature and high pressure gas. One of the common problems of mechanical components, particularly gas turbine blades, is fatigue cracking which usually occurs under variable loading due to the start and shutdown process and vibrations. Low-cycle fatigues are caused by the stress induced by high centrifugal force due to high rotational speed and thermal loads triggered by temperature gradients in startup and shutdown of gas turbine, as well as operation at critical environmental conditions. The present study aimed at presenting the mechanism and modeling of fatigue crack initiation and propagation in CM186 LC directional solidified material of a first-stage gas turbine blade. To investigate the crack initiation point, a finite element study was carried out using ABAQUS software package. The stress distribution of the blade was calculated in accordance with engine conditions and the fatigue crack growth was then predicted by using ZENCRACK fracture mechanics code. Moreover, the Paris model was used in this study to estimate the fatigue life. The stress intensity factors (KI & KII) of individual mode and fracture mechanics quantities were calculated from CTOD and J-Integral methods, followed by the computation of crack growth direction on the basis of maximum energy release rate criterion.