Fatigue Life Prediction Modeling for Turbine Hot Section Materials

Abstract

This paper presents a summary of the life prediction methods developed under the NASA Lewis Research Center’s Hot Section Technology (HOST) program. A major objective of the fatigue and fracture efforts under the HOST program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This has been achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. Such technical improvements will eventually reduce life cycle costs. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline alloys and highly anisotropic single crystal alloys have been addressed. A sizeable data base has been generated for three alloys [cast PWA 1455 (B–1900 + Hf), wrought Inconel 718, and cast single-crystal PWA 1480] in bare and coated conditions. Two coating systems, diffusion aluminide (PWA 273) and plasma-sprayed MCrAlY overlay (PWA 286), were employed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxially of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) Model of Pratt & Whitney and the Total Strain Version of Strainrange Partitioning (TS-SRP) of NASA Lewis for nominally isotropic materials, and the Tensile Hysteretic Energy Model of Pratt & Whitney for anisotropic superalloys. The fatigue model being developed by the General Electric Company is based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex non-linear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model has been derived by researchers at Syracuse University. The models are described and discussed in the paper. Only limited verification has been achieved to date as several of the technical programs are still in progress and the verification tasks are scheduled, quite naturally, near the conclusion of the program. To date, efforts have concentrated on developement of independent models for cyclic constitutive behavior, cyclic crack initiation, and cyclic crack propagation. The transition between crack initiation and crack propagation has not been thoroughly researched as yet, and the integration of these models into a unified life prediction method has not been addressed.

Influence of fluid-structure interaction modelling on the stress and fatigue life evaluation of a gas turbine blade

“…As such, the decoupled method allows the use of separate solvers without the need in formulating an interface/ coupling algorithm to couple the independent codes. 6 The decoupled approach as implemented in the current analyses involves a single execution of the fluid and solid-side model equations.…”

“…In addition, the recent improvements in the development of these solvers, enable a close-to-ideal model to be replicated in a way to help the further understanding of the dominant damage modes at the design phase. This is important given that for a critical component such as the highpressure turbine blade, an inaccurate life estimation can lead to an overly expensive designs, or that due to underutilization of remaining useful life, Halford et al 6 In this study, a numerical approach of fluidstructure interaction is implemented to investigate the influence of multi-physics coupling on the load response and fatigue life of high-pressure turbine blade. Fluid-Structure Interaction (FSI) is a multidisciplinary solution approach which considers the interaction between the two fields of fluid and structural response.…”

“…This is important given that for a critical component such as the high-pressure turbine blade, an inaccurate life estimation can lead to an overly expensive designs, or that due to underutilization of remaining useful life, Halford et al. 6…”

Application of Spectral Method for Vibration-Induced High-Cycle Fatigue Evaluation of an HP Turbine Blade

“…In the high-cycle failure mode, the resulting blade vibration and induced strains are mostly elastic in nature but occurring 2 Ubulom GTP-20-1395 at very high-frequencies in a short span. This complex interplay requires an accurate life prediction approach which is essential to avoid any likelihood of an overly expensive designed model, or underutilizing the remaining useful life [3].…”

Real Time Fault Monitoring of Industrial Processes

“…However the transition between crack initiation and crack propagation has not been thoroughly researched as yet, to be integrated in a unified life prediction method (Bhargava et al (1986), Lankford and Hudak (1987), Halford et al (1989». Having said that, the problem is: how to estimate the time to failure of a cyclically loaded structural component. However the transition between crack initiation and crack propagation has not been thoroughly researched as yet, to be integrated in a unified life prediction method (Bhargava et al (1986), Lankford and Hudak (1987), Halford et al (1989». Having said that, the problem is: how to estimate the time to failure of a cyclically loaded structural component.…”