Creep-Fatigue Life Prediction Model for Thermal Power Units
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Solution Overview
Problem
Current creep-fatigue life prediction methods for structural parts in thermal power units rely on creep-fatigue tests and neglect the interaction effects between creep, fatigue, and oxidative damage, leading to underestimation of total damage and prolonged service life predictions.
Innovation Solution
A method and system for predicting creep-fatigue life based on pure creep and fatigue data, constructing a creep-fatigue life prediction model using expressions for creep, fatigue, and oxidative damage, which considers the nonlinear interaction among these damages, utilizing stress relaxation curves and material constants to acquire initial damages and iteratively adjust strain energy densities to construct an accurate model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If creep-fatigue test is conducted to acquire stress relaxation curve for life prediction, then prediction can be performed using existing methods, but the process becomes complex and time-consuming
Solution Approach 1:
The patent extracts and separates the creep damage calculation from the complex creep-fatigue test requirement. By using pure creep test data to establish a stress relaxation curve, the method removes the need to conduct separate creep-fatigue interaction tests, thereby simplifying the testing process while maintaining prediction capability
Solution Approach 2:
The patent segments the damage prediction into independent components: creep damage calculated from pure creep tests via stress relaxation curve, fatigue damage from pure fatigue tests, and oxidation damage from environmental conditions. These segmented damage components are then combined through a linear damage rule, avoiding the need for complex integrated creep-fatigue testing
2Ease of operation
If bilinear damage frame is used for creep-fatigue life prediction, then calculation is simplified, but the interaction effect among creep, fatigue and oxidative damage is neglected leading to underestimation
Solution Approach 1:
The patent modifies the traditional bilinear damage approach by introducing a stress relaxation curve derived from pure creep data. This changes the parameter representation of creep damage from direct stress-strain relationships to a time-dependent relaxation framework, enabling more accurate capture of creep-fatigue-oxidation interactions while maintaining computational feasibility
Solution Approach 2:
The patent creates a composite damage model that integrates three distinct damage mechanisms (creep, fatigue, oxidation) into a unified life prediction framework. Each mechanism is modeled separately using appropriate parameters and then combined through damage accumulation rules, creating a composite approach that captures interaction effects better than simple linear superposition
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach overcomes the need for creep-fatigue test data, reduces conversion errors, and provides a more accurate prediction of creep-fatigue life by considering the interaction effects, resulting in a more reliable evaluation of high-temperature structural part service life.
Implementation Method 1
A structural part of a thermal power unit serves in a high-temperature and high-pressure stream environment to generate a creep damage
Implementation Method 2
acquire an initial creep damage according to a stress relaxation curve of the structural part of the thermal power unit
Implementation Method 3
bears cyclic stress caused by short-time temperature and load fluctuation to generate a fatigue damage
Implementation Method 4
the accelerating effect of the oxidative damage on the creep damage and the fatigue damage
Data Source
AI summary
The present invention discloses a method and system for predicting a creep-fatigue life of a structural part of a thermal power unit. The method includes: constructing a life prediction model; acquiring a stress relaxation curve in a strain control creep-fatigue test through pure creep data to calculate an initial creep damage; acquiring a cyclic hardening coefficient, an elasticity modulus and other related material constants through the pure fatigue data to calculate an initial fatigue damage; and acquiring a difference between strain energy densities in upper and lower parts of creep-fatigue mean stress, making the difference between strain energy densities less than a set threshold through dichotomy iteration to acquire a final creep damage, a final fatigue damage and an oxidative damage under such a circumstance, and predicting the creep-fatigue life of the high-temperature structural part based on the life prediction model.