Creep Modeling of 9-12%Cr Ferritic Steels Accounting for Subgrain Size Evolution

2018 ◽  
Author(s):  
Luca Esposito ◽  
Gabriel Testa ◽  
Alcide Bertocco ◽  
Nicola Bonora
Keyword(s):  
Creep Rate ◽  
Damage Mechanics ◽  
Subgrain Size ◽  
Equilibrium Phase ◽  
Continuum Damage Mechanics ◽  
Creep Model ◽  
Ferritic Steels ◽  
State Variables ◽  
Size Evolution ◽  
Creep Resistant Steels

The enhanced performance of new creep-resistant steels is the result of optimized microstructures. Clearly, the microstructure stability at high temperature is essential for the long-term use of this steels generation. In the recent scientific literature, several research addresses the correlation between the microstructure degradation and the creep performance loss. General aim is to introduce state variables able to describe the metallurgy history of the material affecting its current and future response. The possibility to integrate this metallurgical information in predictive modeling is very attractive. In this work, a new creep model for 9-12%Cr ferritic steels, in the framework of the Continuum Damage Mechanics (CDM), is proposed. The damage variable, usually not related to the underlying physics, may have a metallurgical meaning introducing the kinetic law for subgrain evolution. The microstructure of 9-12%Cr steels is designed to produce the 100% martensite during quenching treatment. Since martensite is not a thermodynamic equilibrium phase, the microstructure evolves exhibiting lath widening and subgrains coarsening. The subgrains growth can be ascribed to the creep strain accumulation and consequently the proposed formulation uses the subgrain size evolution to predict the creep rate beyond the minimum creep rate mainly affected by the recovery processes.

Creep Life Prediction of Aircraft Turbine Disc Alloy Using Continuum Damage Mechanics

2017 ◽  
Vol 38 (1) ◽  
pp. 25-30
Author(s):  
Yan-Feng Li ◽  
Zhisheng Zhang ◽  
Chenglin Zhang ◽  
Jie Zhou ◽  
Hong-Zhong Huang
Keyword(s):  
Numerical Analysis ◽  
Test Data ◽  
Life Prediction ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Creep Model ◽  
Continuum Damage ◽  
Creep Life ◽  
Creep Life Prediction ◽  
Turbine Disc

Abstract This paper deals with the creep characteristics of the aircraft turbine disc material of nickel-base superalloy GH4169 under high temperature. From the perspective of continuum damage mechanics, a new creep life prediction model is proposed to predict the creep life of metallic materials under both uniaxial and multiaxial stress states. The creep test data of GH4169 under different loading conditions are used to demonstrate the proposed model. Moreover, from the perspective of numerical simulation, the test data with analysis results obtained by using the finite element analysis based on Graham creep model is carried out for comparison. The results show that numerical analysis results are in good agreement with experimental data. By incorporating the numerical analysis and continuum damage mechanics, it provides an effective way to accurately describe the creep damage process of GH4169.

Damage mechanics-based creep model for 9–10%Cr ferritic steels

2011 ◽  
Vol 59 (5) ◽  
pp. 2145-2155 ◽  
Author(s):  
R. Oruganti ◽  
M. Karadge ◽  
S. Swaminathan
Keyword(s):  
Damage Mechanics ◽  
Creep Model ◽  
Ferritic Steels

Unified Viscoplastic Model Coupled With Damage for Evaluation of Creep-Fatigue of Grade 91 Steel

2017 ◽  
Author(s):  
Nazrul Islam ◽  
David J. Dewees ◽  
Tasnim Hassan
Keyword(s):  
Damage Mechanics ◽  
Creep Damage ◽  
Continuum Damage Mechanics ◽  
Creep Model ◽  
Damage Evaluation ◽  
Creep Fatigue ◽  
Grade 91 ◽  
Term Creep ◽  
Grade 91 Steel

A continuum damage mechanics (CDM) coupled unified viscoplasticity model has been developed to predict the creep-fatigue life of modified Grade 91 steel. A tertiary creep model termed MPC-Omega codified in Part 10 of API (and also implemented in the ASME BP&V Code for Grade 22V and more recently Grade 91 Steel) is also employed for creep damage evaluation. As MPC-Omega has a direct relationship with Larson-Miller parameter (LMP) coefficients, creep damage coefficients in the unified constitutive model (UCM) are tied with MPC-Omega coefficients in order to utilize WRC and API 579-1 Grade 91 creep rupture database. The model is validated against long-term creep, LCF, creep-fatigue and TMF experimental responses at T = 20–600°C.

An Improved Mechanism-Based Creep Constitutive Model Using Stress-Dependent Creep Ductility

2016 ◽  
Author(s):  
Yu Zhou ◽  
Chen Xuedong ◽  
Zhichao Fan ◽  
Han Yichun
Keyword(s):  
Damage Mechanics ◽  
Constitutive Models ◽  
Continuum Damage Mechanics ◽  
Creep Process ◽  
Ferritic Steels ◽  
Creep Tests ◽  
Creep Ductility ◽  
Wide Range ◽  
Stress Levels ◽  
Stress Dependent

Creep ductility which is assumed to be constant at a given temperature in many creep constitutive models, actually varies with temperature, stress level and creep strain rate, etc. In this paper, the relationship between creep ductility and stress levels of ferritic steels has been briefly discussed from the perspective of failure mechanisms. It can be generally divided into three regimes, including the upper shelf, lower shelf and the transition regime. The four-parameter logistic model has been adopted to quantitatively describe the stress-dependent creep ductility. Furthermore, a modified mechanism-based continuum damage mechanics (CDM) model for ferrtic steels has been proposed using the stress-dependent creep ductility model. Uniaxial creep tests of 2.25Cr1Mo0.25V steel at three stress levels have been carried out and the experimental data points realistically reflecting the creep behavior have been carefully selected to fit the improved CDM model using genetic algorithm (GA). It is shown that the improved model has the capability to characterize the whole creep process of ferritic steels and the stress-dependent creep ductility over a wide range of applied stress.

Stress Relaxation Continuum Damage Constitutive Equations for Relaxation Performance Prediction

2012 ◽  
Vol 455-456 ◽  
pp. 1434-1437
Author(s):  
Jin Quan Guo ◽  
Wei Zhang ◽  
Xiao Hong Sun
Keyword(s):  
Stress Relaxation ◽  
Constitutive Equations ◽  
Damage Mechanics ◽  
Constitutive Models ◽  
Continuum Damage Mechanics ◽  
Creep Model ◽  
Continuum Damage ◽  
Relaxation Equation ◽  
Creep Tests ◽  
Analysis Technique

Stress relaxation constitutive equations based on Continuum Damage Mechanics, Kachanov-Robatnov creep model, and stress relaxation equation has been developed by analyzing stress relaxation damage mechanisms and considering the relationship that stress relaxation is creep at various stresses. And, the constitutive differential equations were integrated to predict stress relaxation performance by using numerical analysis technique. In order to validate the approach, the predicted results are compared to the experimental results of uni-axial isothermal stress relaxation tests conducted on 1Cr10NiMoW2VNbN steel with the same temperature of creep tests. Good agreement between results of relaxation tests and the predicted results indicates that the developed constitutive models can be used in the relaxation behavior evaluation of high temperature materials.

Comparative Study of Creep Behavior in 9Cr-1Mo Steel With Different Prediction Methods

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Lin Zhu ◽  
Xinbao Liu ◽  
Ping Fan ◽  
Jianqiu Liu ◽  
Chengfei Pan
Keyword(s):  
Creep Rate ◽  
Minimum Creep Rate ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Model Combination ◽  
Creep Life ◽  
Physically Based ◽  
Term Creep ◽  
Short Term Creep

Abstract Over the range of variables (temperature and stress) normally encountered in service applications, creep behaviors of 9Cr-1Mo steel were investigated with various models, such as Wilshire model, combination of exponential form and omega (CEO) model, and continuum damage mechanics (CDM) model. First, a series of short-term creep data was prepared to evaluate the material parameters occurring in these models. Then, creep curve, minimum creep rate, and long-term creep life of present 9Cr-1Mo steel were extrapolated with these estimated models. Based on the analysis of obtained results in detail, it suggested that both CDM model and CEO model can give reliable minimum creep rate predictions. However, the most reliable values of long-term creep life are obtained by the CDM model, followed by the Wilshire model and then the CEO model. In particular, the physically based CDM model can provide useful insights into the underlying creep mechanisms. Therefore, the CDM model has promising potential to study the long-term creep behaviors of 9Cr-1Mo steels.

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