The Application of the Combined Creep and Rate-Independent Plasticity Model to Turbine Components Life Prediction

Abstract

The understanding of micromechanics of the high temperature creep, plasticity, and damage accumulation in single crystal nickel base superalloys is important for the design of turbine blades and vanes in advanced commercial and military gas turbines. We developed the crystallographic–based viscoplastic model for non-isothermal high temperature cyclic deformation and coupled it with damage kinetics. Damage accumulation causes tertiary creep and shear localization around local concentrators, which is essential for airfoil life prediction. We develop a new robust, computationally efficient rate-independent crystal plasticity approach and combined it with creep flow rule calibrated for Ni-based superalloys. Engine operating conditions were assembled into a mission profile, an input to the transient thermal analysis. Non-linear transient thermal-structural analysis of a turbine airfoil provides the illustration of the life prediction for different engine operating conditions. We compare the predictions for low cycle and thermal mechanical fatigue for smooth specimen tests and for notched specimens and demonstrate the transition from safe life to damage tolerant approach. The constitutive model has been implemented in the commercial finite element software ANSYS as a material user routine. The effects of single crystal orientation and stress relaxation and redistribution, cycles parameters, strain levels, and dwell time have been numerically obtained. The model results are used for predicting of thermal cyclic behavior and damage of single crystal airfoil.