Keywords

Creep Accelerated Theta-Projection

Abstract

The demand for efficiency in power generation and propulsion requires higher firing temperatures and reduced cooling air consumption which raises metal temperatures. This makes simplistic creep evaluations, such as Larson-Miller and Orr-Sherby-Dorn parameters, inadequate. Finite element analysis (FEA) must simulate primary and secondary creep, predict failure, and provide design guidance. Gas turbine components, expected to last over 100,000 hours, often require extrapolation of limited test data for new materials. It is essential that robust creep simulations be developed efficiently, accurately, and effectively use limited test data.

This dissertation describes an optimized framework for efficient creep testing and rapid construction of implicit creep models for finite element simulations.  A combined approach using conventional and accelerated (stepped) tests is presented to create two forms of Modified Theta Projection models (MTPM and MTPMp).  The fitting methods include compensation for the evolution of true stress and true strain during testing, especially for ductile alloys.  A wide variety of stress-temperature relationships can be selected based on a thorough exploration of creep parameter relationships.  A combined strain plus life-fraction hardening model was developed to include the interaction of primary creep and plasticity.  This combined hardening model captures effects like diminished creep life after plastic yielding and additional primary creep experienced with increasing load steps.  The concept of temperature margins for creep was refined to provide input for required temperature changes to meet life requirements.  The temperature margins are further improved to allow for the stochastic nature of creep by determining margins that consider the uncertainty of creep models.  Together, these contributions enable the development of accurate and efficient creep models from limited test data, supporting safer and more reliable high-temperature component design.

Completion Date

2026

Semester

Fall

Committee Chair

Gordon, Ali

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

MAE

Format

PDF

Document Type

Thesis

Identifier

DP0053101

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