Fatigue Life Estimation Procedure for a Turbine Blade Under Transient Loads

Abstract

Fatigue analysis and consequent life prediction of turbomachine blading requires the stress load history of the blade. A blade designed for safe operations at particular constant rotor speeds may, however, incur damaging stresses during Start-up and Shut-down operations. During such operations the blade experiences momentary resonant stresses while passing through the criticals which may lie in the speed range through which the rotor is accelerated. Fatigue due to these transient influences may cumulate to lead to failure. In this paper a technique for fatigue damage assessment during variable speed operations is presented. Transient resonant stresses for a blade with nonlinear damping have been determined using a numerical procedure. A fatigue damage assessment procedure is described. The fatigue failure surface is generated on the S-N-mean stress axes and Miner’s Rule is employed to estimate the cumulation of fatigue.