Creep Strength Analysis for High-Temperature Components
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Solution Overview
Problem
Current high-temperature component creep strength evaluation methods rely solely on single mechanical variables, such as strain or stress, leading to overly conservative designs and neglecting shear stress failures, which limits the service potential and safety of high-temperature structures like steam turbine rotors.
Innovation Solution
A creep strength analysis and assessment method based on both strain and stress criteria, incorporating multiaxial correction coefficients and shear stress evaluation, to determine the safety and service potential of high-temperature components, particularly in discontinuous parts, using the Norton-Bailey constitutive equation and finite element methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a strain-based creep strength evaluation strategy using multiaxial stress correction coefficients is used, then creep deformation is controlled, but the design becomes overly conservative and service potential cannot be fully exploited
Solution Approach 1:
The patent transitions from a pure strain-based evaluation to a stress-based evaluation with a strain criterion as supplement. This parameter change in the evaluation basis allows full exploitation of material service potential while maintaining creep strength through the strain criterion check in specific discontinuous regions.
2Stress or pressure
If a stress classification method is used to restrict membrane and bending stresses, then stress level is controlled, but shear stress failure mode is not considered
Solution Approach 1:
The patent segments the stress evaluation into two independent parts: stress criterion evaluation (membrane and bending stresses) and shear stress criterion evaluation. This segmentation allows each criterion to address specific failure modes independently, ensuring comprehensive safety coverage including shear stress failures in discontinuous regions.
3Device complexity
If a single parameter evaluation method is used, then the evaluation procedure is simple, but it cannot fully assess both creep deformation and rupture risk
Solution Approach 1:
The patent implements a dynamic two-criteria evaluation system where the stress criterion and strain criterion work together. The stress criterion (PL, Pb, τ) assesses rupture risk, while the strain criterion (εm, εeq) assesses creep deformation. This dynamic combination provides comprehensive assessment accuracy while maintaining procedural clarity through defined evaluation steps.
Data Source
AI summary
A creep strength analysis and assessment method includes comparing whether a maximum value of a local strain and a membrane strain are less than a corresponding allowable strain, and if less, determining that a component is safe; otherwise, performing the following steps: performing stress linearization on a path to obtain a local primary membrane stress PL and a local primary bending stress Pb; averaging shear stress components on the path to obtain an average shear stress τm; obtaining a strength limit Smt, a time-independent minimum stress strength value Sm and a temperature- and time-dependent stress strength limit St for a given material, a design lifetime and a design temperature; comparing whether PL, PL+Pb and PL+Pb/Kt are less than Smt, KSm and St; and comparing whether τm is less than 0.6Sm and 0.6St, and if less, the component is safe, otherwise, the component is unsafe.