Analysis of Multi-Axial Creep–Fatigue Damage on an Outer Cylinder of a 1000 MW Supercritical Steam Turbine

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Weizhe Wang
Keyword(s):  
Steam Turbine ◽  
Fatigue Damage ◽  
Damage Mechanics ◽  
Hydrostatic Stress ◽  
Fatigue Behavior ◽  
Axial Stress ◽  
Outer Cylinder ◽  
Continuum Damage Mechanics ◽  
Transfer Coefficients ◽  
Creep Fatigue

A multi-axial continuum damage mechanics (CDM) model was proposed to calculate the multi-axial creep–fatigue damage of a high temperature component. A specific outer cylinder of a 1000 MW supercritical steam turbine was used in this study, and the interaction of the creep and fatigue behavior of the outer cylinder was numerically investigated under a startup–running–shutdown process. To this end, the multi-axial stress–strain behavior of the outer cylinder was numerically studied using Abaqus. The in-site measured temperatures were provided to validate the heat transfer coefficients, which were used to calculate the temperature field of the outer cylinder. The multi-axial mechanics behavior of the outer cylinder was investigated in detail, with regard to the temperature, Mises stress, hydrostatic stress, multi-axial toughness factor, multi-axial creep strain, and damage. The results demonstrated that multi-axial mechanics behavior reduced the total damage.

A Practical Elastic Plastic Damage Model for Concrete

2011 ◽  
Vol 243-249 ◽  
pp. 313-318 ◽  
Author(s):  
Hu Qi ◽  
Yun Gui Li ◽  
Xi Lin Lu
Keyword(s):  
Stress State ◽  
Damage Mechanics ◽  
Hydrostatic Stress ◽  
Axial Stress ◽  
Stress Component ◽  
Damage Model ◽  
Continuum Damage Mechanics ◽  
Deviatoric Stress ◽  
Elastic Plastic ◽  
Plastic Damage

In this paper, an elastic plastic damage model is presented based on the combined use of elastic plastic constitutive equations along with continuum damage mechanics. A tensile and a compressive damage variable are adopted to describe the different responses of concrete under tension and compression, respectively. The Helmholtz Free Energy is decomposed into hydrostatic stress component and deviatoric stress components. The hydrostatic stress component is neglected and the deviatoric stress component is amended according to stress state, resulting in a more accurate description of the concrete’s response under multi-axial stress state. Finally, through several numerical simulations it is proved that the proposed model has the capability of simulating typical nonlinear performances of concrete material.

Multiaxial Creep-Fatigue Life Prediction on the Rotor of a 1000MW Supercritical Steam Turbine

2012 ◽  
Author(s):  
Jianfeng Mao ◽  
Weizhe Wang ◽  
Yingzheng Liu ◽  
Junhui Zhang
Keyword(s):  
High Temperature ◽  
Steam Turbine ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Mechanics Model ◽  
Creep Fatigue ◽  
Damage Accumulation Model ◽  
Multiaxial Creep ◽  
Comparison Of The Results

Damage of a high temperature rotor subjected to the creep-fatigue interaction was numerically investigated. Toward that end, a high temperature rotor of a 1000MW supercritical steam turbine was chosen for the study. A continuum damage mechanics model (CDM), which depicts the fatigue-creep interaction, was developed in the present paper. During the practical startup and shutdown processes, the influence of the multiaxial creep-fatigue interaction on strength of the rotor was analyzed in terms of stress, strain and damage. Comparison of the results from linear damage accumulation model (LDA) and CDM demonstrated that CDM was more reasonable to predict the lifetime of the rotor due to the multiaxial creep-fatigue interaction.

A Continuum Damage Mechanics-Based Viscoplastic Model of Adapted Complexity for High-Temperature Creep–Fatigue Loading

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Weizhe Wang ◽  
Patrick Buhl ◽  
Andreas Klenk ◽  
Yingzheng Liu
Keyword(s):  
Damage Mechanics ◽  
Fatigue Behavior ◽  
Continuum Damage Mechanics ◽  
Fatigue Loading ◽  
Material Model ◽  
Material Behavior ◽  
Continuum Damage ◽  
Loading Test ◽  
Constitutive Material Model ◽  
Creep Fatigue

A continuum damage mechanics (CDM) based viscoplastic constitutive model is established in this study to describe the fully coupling of creep and fatigue behavior. The most significant improvement is the introduction of a continuum damage variable into the constitutive equations, instead of considering creep damage and fatigue damage separately. The CDM-based viscoplastic constitutive material model is implemented using a user-defined subroutine (UMAT). A standard specimen is used for carrying out uniaxial creep, fatigue, and creep–fatigue interaction tests to validate the material model. In addition, to further demonstrate the capability of the material model to predict the complex material behavior, a complex strain-control loading test is performed to validate the material model. The simulated and measured results are in good agreement at different temperatures and loadings, in particular for rapid cyclic softening behavior following crack initiation and propagation.

Creep-Fatigue Life Prediction of Stop and Regulating Valves on the Intermediate-Pressure Section of a 1000MW Steam Turbine

2013 ◽  
Author(s):  
Jianfeng Mao ◽  
Junhui Zhang ◽  
Weizhe Wang ◽  
Yingzheng Liu
Keyword(s):  
Fatigue Life ◽  
Steam Turbine ◽  
Life Prediction ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Complex Stress ◽  
Fatigue Life Prediction ◽  
Temperature Fields ◽  
Intermediate Pressure ◽  
Creep Fatigue

The stop&regulating integrated valve on the intermediate-pressure (IP) section of a 1000MW steam turbine is presented in this paper. A multiaxial model based on continuum damage mechanics (CDM) is applied to life prediction of the valve. The transient stress and the temperature fields of the valve in a 1000MW supercritical steam turbine are investigated by using finite element method (FEM) for fatigue-creep. Since the turbine typically runs 120 days between starts, a simplified mission profile for a 120-day block was created. Accordingly, the 120-day loading block with plasticity and creep was run repetitively to achieve a 22 years creep-fatigue life prediction. The interaction between creep and fatigue was considered in total damage in proper order. Due to highly complex stress and structure, the multiaxial factors for fatigue and creep are assessed from the temporal and spatial points of view respectively. Furthermore, the creep-fatigue damage of the integrated valve is discussed in relation to the multiaxial factors. The results drawn from the multiaxial CDM model give a satisfactory life prediction on the valve.

Numerical Investigation of Creep–Fatigue Behavior in a Steam Turbine Inlet Valve Under Cyclic Thermomechanical Loading

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Weizhe Wang ◽  
Sihua Xu ◽  
Yingzheng Liu
Keyword(s):  
Steam Turbine ◽  
Contact Stress ◽  
Damage Mechanics ◽  
Fatigue Behavior ◽  
Thermomechanical Loading ◽  
Inlet Valve ◽  
Valve Body ◽  
Turbine Inlet ◽  
Creep Fatigue ◽  
Cyclic Thermomechanical Loading

The aim of this study was to investigate the cyclic creep–fatigue interaction behavior in a steam turbine inlet valve under cyclic thermomechanical loading conditions. Three years and nine iterations of idealized startup–steady-state operation–shutdown process were chosen. The Ramberg–Osgood model, the Norton–Bailey law, and continuum damage mechanics were applied to describe the stress–strain behavior and calculate the damage. The strength of the steam valve revealed that significant stress variation mainly occurred at the joint parts between the valve diffuser and the adjust valve body, due to the combination of the enhanced turbulent flow and assembly force at these areas. The contact stress at the region of component assembly was sensitive to the cyclic loading at the initial iterations. The maximum decrease amplitude in the normalized contact stress between the second and the fourth iterations reached 0.12. The damage analysis disclosed that the notch of the deflector in the adjust valve had the maximum damage due to the stress concentration.

Fatigue Damage Analysis of Double-Lap Bolted Joints Considering the Effects of Hole Cold Expansion and Bolt Clamping Force

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Ying Sun ◽  
George Z. Voyiadjis ◽  
Weiping Hu ◽  
Qingchun Meng ◽  
Yuanming Xu
Keyword(s):  
Fatigue Damage ◽  
Damage Mechanics ◽  
Fatigue Behavior ◽  
Continuum Damage Mechanics ◽  
Material Behavior ◽  
Bolted Joints ◽  
Clamping Force ◽  
Bolted Joint ◽  
Cold Expansion ◽  
Two Factors

Hole cold expansion and bolt clamping force are usually applied to improve the fatigue performance of bolted joints. In order to investigate the effects of hole cold expansion and bolt clamping force and reveal the mechanism of these two factors on the fatigue damage of bolted joint, a continuum damage mechanics (CDM) based approach in conjunction with the finite element method is used. The damage-coupled Voyiadjis plasticity constitutive model is used to represent the material behavior, which is implemented by user material subroutine in abaqus. The elasticity and plasticity damage evolutions of the material are described by the stress-based and plastic-strain-based equations, respectively. The fatigue damage of joint is calculated using abaqus cycle by cycle. The fatigue lives of double-lap bolted joints with and without clamping force at different levels of hole cold expansion are all obtained. The characteristics of fatigue damage corresponding to the different conditions are presented to unfold the influencing mechanism of these two factors. The predicted fatigue lives and crack initiation locations are in good agreement with the experimental results available in the literature. The beneficial effects of hole cold expansion and bolt clamping force on the fatigue behavior of bolted joint are presented in this work.

Development of continuum damage in the creep rupture of notched bars

1984 ◽  
Vol 311 (1516) ◽  
pp. 103-129 ◽  
Keyword(s):  
New York ◽  
Damage Mechanics ◽  
Axial Stress ◽  
Numerical Procedure ◽  
Creep Damage ◽  
Continuum Damage Mechanics ◽  
Constant Load ◽  
Creep Rupture ◽  
Continuum Damage ◽  
Discrete Crack

The creep rupture of circumferentially notched, circular tension bars which are subjected to constant load for long periods at constant temperature is studied both experimentally and by using a time-iterative numerical procedure which describes the formation and growth of creep damage as a field quantity. The procedure models the development of failed or cracked regions of material due to the growth and linkage of grain boundary defects. Close agreement is shown between experimental and theoretical values of the representative rupture stress, of the zones of creep damage and of the development of cracks for circular (Bridgman, Studies in large plastic flow and fracture , New York: McGraw-Hill (1952)) and British Standard notched specimens (B.S. no. 3500 (1969)). The minimum section of the circular notch is shown to be subjected to relatively uniform states of multi-axial stress and damage while the B.S. notch is shown to be subjected to non-uniform stress and damage fields in which single cracks grow through relatively undamaged material. The latter situation is shown to be analogous to the growth of a discrete crack in a lightly damaged continuum. The continuum damage mechanics theory presented here is shown to be capable of accurately predicting these extreme types of behaviour.

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