A Novel Methodology to Estimate Life of Gas Turbine Components Under Multiaxial Variable Amplitude Loading
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TECHNICAL ARTICLE—PEER-REVIEWED
A Novel Methodology to Estimate Life of Gas Turbine Components Under Multiaxial Variable Amplitude Loading R. K. Mishra . S. Dileep
Submitted: 1 July 2017 / Published online: 18 July 2017 ASM International 2017
Abstract A novel and highly effective methodology is presented in this study to estimate the stresses and strains and also the life of gas turbine components operating in multiaxial variable amplitude loading conditions. The methodology uses a cyclic plasticity model based on multilinear kinematic hardening (MLKH) for estimation of stress-strain response and Wang and Brown algorithm for counting the reversals in the loading cycle. The stress and strain response extracted for each reversal using the MLKH model where then integrated with multiaxial fatigue damage model based on critical planes (Wang and Brown model) suitable for LCF applications, to predict the fatigue life. The proposed methodology was initially compared with experimental test results of 42CrMo4 low alloy steel specimen, under different loading conditions like proportional, non-proportional and sequential loadings available in the literature. To reinforce the life prediction capability of the methodology, an application level study was undertaken. An air-cooled high-pressure turbine disk of an aero gas turbine engine was used as the model for this study. The fatigue life obtained from the multiaxial fatigue damage model was then compared with the experimental LCF life of the disk obtained from the field data. In order to be conservative in approach, lower bound of the 95% confidence limit of the fatigue data fitted using Weibull probability distribution function was used to compare the numerical life. The study shows a good correlation between
R. K. Mishra (&) Regional Center for Military Airworthiness, Bangalore, India e-mail: [email protected] S. Dileep Aero Engine Research and Design Centre, Bangalore, India
the fatigue life arrived experimentally and the predicted life using the proposed methodology. Keywords Multilinear kinematic hardening Thermo-mechanical analysis Variable amplitude loading Multiaxial fatigue
Introduction Estimation of the life under multiaxial loading conditions has remained a daunting task. By reviewing available state-of-the-art research works [1, 2], it is clear that, some of the issues which complicate the life estimation under such conditions are: loading conditions which can be nonproportional and variable in amplitude in many applications, uncertainty over the damage models which has to be used for a particular application, estimation of the mean and the amplitude value of the shear stresses or strain in the critical plane, models to be used to the count the reversals in a multiaxial variable amplitude loading history, models to be used for estimation of stresses and strains in the notches and geometric discontinuities and damage accumulation models to be used in cases of multiple reversals. Enormous research work has taken place in the field of multiaxial loadi
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