scholarly journals Fatigue–Creep Interaction of P92 Steel and Modified Constitutive Modelling for Simulation of the Responses

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 307
Author(s):  
Tianyu Zhang ◽  
Xiaowei Wang ◽  
Wei Zhang ◽  
Tasnim Hassan ◽  
Jianming Gong
Keyword(s):  
Fatigue Life ◽  
Constitutive Model ◽  
Dwell Time ◽  
Kinematic Hardening ◽  
Model Development ◽  
Strain Range ◽  
Peak Stress ◽  
Constitutive Modelling ◽  
P92 Steel ◽  
Static Recovery

Fatigue–creep interaction (FCI) responses of P92 steel are investigated experimentally and numerically. A series of isothermal FCI experiments with tensile dwell time ranging from 60 to 600 s were conducted at two temperatures under strain-controlled trapezoidal waveform. The experimental responses demonstrate that the peak stress is influenced by temperature and dwell time. In other words, creep-mechanism-influenced stress relaxation during dwell time influences the peak stress and fatigue life (Nf). In addition, effects of strain range on peak stress and fatigue life under fatigue–creep loading are evaluated. Towards developing a simulation-based design methodology for high temperature components, first a conventional unified constitutive model is evaluated against the P92 steel experimental responses. Based on the simulation deficiency of the conventional model, a modified static recovery term incorporated in the kinematic hardening rule is proposed and satisfactory simulations of the P92 steel FCI responses are demonstrated. The experimental responses of P92 steel and strengths and deficiencies of the conventional and modified Chaboche models are elaborated identifying the important FCI phenomena and progress in constitutive model development for FCI response simulation.

A Unified Viscoplastic Model for Creep and Fatigue-Creep Response Simulation of Haynes 230

2015 ◽  
Author(s):  
Paul Ryan Barrett ◽  
Tasnim Hassan
Keyword(s):  
Constitutive Model ◽  
Kinematic Hardening ◽  
Strain Range ◽  
Parameter Determination ◽  
Secondary Creep ◽  
Damage Modeling ◽  
Haynes 230 ◽  
Static Recovery ◽  
Hardening Rules ◽  
Creep Regime

A Chaboche-based unified viscoplastic constitutive model, including features of strain range dependence, strain rate-dependence, static recovery, and mean stress evolution is developed and evaluated for simulating fatigue-creep and creep responses of Haynes 230. In other words, this constitutive model attempt to simulate not only strain-controlled fatigue and fatigue-creep responses of Haynes 230, but also stress-controlled creep responses. After investigating various flow rules and kinematic hardening rules, a unified viscoplastic constitutive model is developed for simulating both the fatigue-creep and creep responses. The parameter determination for this constitutive model, however, requires a robust optimization algorithm. The proposed unified constitutive model can adequately simulate fatigue-creep responses, and creep responses up to the secondary creep regimes. However, with the introduction of damage modeling features the constitutive model can simulate the tertiary creep regime responses, but with some limitations in simulating fatigue-creep responses. Nonetheless, the unified viscoplastic constitutive model with or without damage modeling features has shown to be able to capture the stress-controlled creep responses while still maintaining high fidelity in capturing the strain-controlled fatigue and fatigue-creep responses.

High Temperature Constitutive Model Development for Alloy 617

2014 ◽  
Author(s):  
Shahriar Quayyum ◽  
Patrick Graham Pritchard ◽  
Tasnim Hassan
Keyword(s):  
Constitutive Model ◽  
Model Development ◽  
Strain Range ◽  
Cyclic Hardening ◽  
Design Code ◽  
Model Framework ◽  
Alloy 617 ◽  
Static Recovery ◽  
Operation Temperature ◽  
Creep Fatigue

One of the most challenging tasks in the design code development for Next Generation Nuclear Plant (NGNP) is the design of intermediate heat exchanger (IHX), whose operation temperature may range from 800°C–950°C (1472°F–1742°F). The ASME design code does not have any design provisions for any material at this temperature range. Hence, different candidate materials are under consideration for IHX and one of the leading candidate materials is Ni based Alloy 617. The operating temperature of IHX will be in the creep regime of Alloy 617 and low-cycle creep-fatigue and creep-ratcheting failure mechanisms of Alloy 617 need to be understood. This study is developing a unified constitutive model (UCM) for Alloy 617 based on a broad set of uniaxial and multiaxial creep-fatigue and creep-ratcheting experiments at high temperatures. The experiments were conducted at different temperatures, loading rates and strain ranges prescribing different loading histories. The unified constitutive model was developed based on the Chaboche viscoplastic model framework. Model improvement was performed by including cyclic hardening/softening, dynamic and static recovery, strain rate and strain range dependence, nonproportional loading parameter and multiaxial ratcheting features. The simulated responses of the modified UCM were compared against the broad range of experimental data to demonstrate the robustness of the improved model. The strengths and shortcomings of the model are discussed. Paper published with permission.

Thermomechanical Fatigue Response and Constitutive Modeling for Haynes 230

2016 ◽  
Author(s):  
Machel Morrison ◽  
Raasheduddin Ahmed ◽  
Tasnim Hassan
Keyword(s):  
Constitutive Modeling ◽  
Kinematic Hardening ◽  
Constitutive Models ◽  
Strain Range ◽  
Thermomechanical Fatigue ◽  
Stress Evolution ◽  
Element Analysis ◽  
Haynes 230 ◽  
Static Recovery ◽  
High Temperature Components

Design by analysis is usually performed by commercially available finite element analysis (FEA) software. Constitutive models available in the FEA software are developed and validated using limited experimental data. Hence, a broad set of thermomechanical fatigue experiments with strain dwell at compressive peaks are performed to understand local fatigue failure responses of high temperature components. This study developed a unified viscoplastic model based on nonlinear kinematic hardening of Chaboche type with added features of strain range dependence, rate dependence, temperature dependence, static recovery, and mean stress evolution. The robustness of the constitutive model is demonstrated by comparing its simulations against the experimental responses.

Comparison of Viscoplastic Modeling of an Equiaxed and Directionally Solidified Ni-Base Superalloy

2020 ◽  
Author(s):  
Nathan O’Nora ◽  
Alex Torkaman ◽  
Ali P. Gordon
Keyword(s):  
Constitutive Model ◽  
Parameter Identification ◽  
Kinematic Hardening ◽  
Complex Loading ◽  
Cyclic Loads ◽  
Loading Conditions ◽  
Directionally Solidified ◽  
Static Recovery ◽  
Non Linear ◽  
Creep Fatigue

Abstract Engine components are subjected to both high temperatures and cyclic loads resulting in fatigue and creep effects. Directionally-solidified (DS) Ni-base superalloys were developed in order to produce favorable creep properties in the primary stress axis of turbine blades by casting the grains longer along this axis. Doing so causes the material to exhibit anisotropic behavior, which allows for improved fatigue and creep strength but also adds complexity to modeling the material. To predict the life of components accurately, it is necessary to use a high-fidelity constitutive model to relate the loading and the deformation of the material. The dual-phase microstructure of these DS superalloys evolves with time, rendering the yield surface of the material a challenge to track. Furthermore, components made from these materials are subjected to complex loading conditions, often seeing cycling temperature in addition to loads, known as thermomechanical fatigue (TMF), and cyclic loads with dwells, known as creep-fatigue (CF). Viscoplasticity models are able to capture the complex behaviors of these materials under complex loading conditions, including the hysteresis effects, rate-dependence, and stress relaxation, etc., making them attractive models to use with critically heated and loaded parts. These models, originally designed for equiaxed materials, have been adapted for use with anisotropic materials, such as DS superalloys. An isothermal anisotropic viscoplasticity model and parameter identification framework has been calibrated within a dedicated parameter identification framework. Principally, the constitutive model is based on the Chaboche viscoplasticity model featuring Armstrong-Frederick kinematic hardening. The performance of a preliminary model is presented for both an equiaxed (i.e., conventionally cast, CC) and DS materials within the same strength class, though more data is needed for validation. With regard to the stress relation associated with creep-fatigue, a fitting-technique for the static recovery model that has shown promise in isotropic materials is expanded to capture the behavior of the DS alloy. Previously developed methods for finding kinematic hardening constants for isotropic material based on Ramberg-Osgood constants at various orientations are expanded to an anisotropic case. These techniques allow for the capturing of more complex loading conditions with a limited number of tests, allowing for cost savings when developing the constitutive model. The model is implemented with three non-linear kinematic hardening terms with static recovery, allowing for the capture of rate and hold time effects, and non-linear isotropic hardening, allowing for the capture of cyclic hardening. The ability to capture the low cycle fatigue (LCF) behavior of both the equiaxed and DS alloys are examined through comparisons with test data.

Constitutive Modeling of Haynes 230 for High Temperature Fatigue-Creep Interactions

2014 ◽  
Author(s):  
Paul R. Barrett ◽  
Raasheduddin Ahmed ◽  
Tasnim Hassan
Keyword(s):  
High Temperature ◽  
Nuclear Power ◽  
Low Cycle Fatigue ◽  
Kinematic Hardening ◽  
Model Development ◽  
Strain Range ◽  
Uniaxial Stress ◽  
Cycle Fatigue ◽  
Modeling Framework ◽  
Creep Fatigue

Non-linear stress analysis for high temperature cyclic viscoplasticity is increasingly becoming an important modeling framework for many industries. Simplified analyses are found to be insufficient in accurately predicting the life of components; such as a gas turbine engine of an airplane or the intermediate-heat exchanger of a nuclear power plant. As a result, advanced material models for simulating nonlinear responses at room to high temperature are developed and experimentally validated against a broad set of low-cycle fatigue responses; such as creep, fatigue, and their interactions under uniaxial stress states. . This study will evaluate a unified viscoplastic model based on nonlinear kinematic hardening (Chaboche type) with several added features of strain-range-dependence, rate-dependence, temperature-dependence, static recovery, and mean-stress-evolution for Haynes 230database. Simulation-based model development for isothermal creep-fatigue responses are all critically evaluated for the developed model. The robustness of the constitutive model is demonstrated and weaknesses of the model to accurately predict low-cycle fatigue responses are identified. Paper published with permission.

Strain Rate Dependent Constitutive Model of Multiaxial Ratchetting of 63Sn–37Pb Solder

2006 ◽  
Vol 129 (3) ◽  
pp. 278-286 ◽  
Author(s):  
Gang Chen ◽  
Xu Chen ◽  
Kwang Soo Kim ◽  
Mohammad Abdel-Karim ◽  
Masao Sakane
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Shear Strain ◽  
Kinematic Hardening ◽  
Axial Stress ◽  
Strain Range ◽  
Strain Rates ◽  
Shear Strain Rate ◽  
Viscous Term ◽  
Ratcheting Strain

A series of multiaxial ratcheting tests were conducted on 63Sn–37Pb solder. A unified viscoplastic constitutive model was developed on the basis of the Ohno–Wang kinematic hardening model, and the rate dependence of the material was taken into consideration by introducing a viscous term. The stress-strain hysteresis loop of 63Sn–37Pb under different strain rates can be simulated reasonably well by the model. However, since the axial ratcheting strain rate of 63Sn–37Pb solder is strongly dependent on the applied shear strain rates in axial/torsional ratcheting, the original constitutive model fails to describe the effect of shear strain rate on the ratcheting strain. To improve the rate sensitivity of the model, the material parameter μi was correlated to the strain rate. Comparisons of the experimental and simulated results verify that the modified constitutive model is able to predict the complicated deformation of 63Sn–37Pb. The effects of axial stress, shear strain range, loading history, and strain rate on ratcheting behavior can be reflected fairly well.

Unified Viscoplasticity Modeling Features Needed for Simulation of Grade 91 Creep and Fatigue Responses

2016 ◽  
Author(s):  
Nazrul Islam ◽  
Dave Dewees ◽  
Tasnim Hassan
Keyword(s):  
Model Simulation ◽  
Low Cycle Fatigue ◽  
Kinematic Hardening ◽  
Strain Range ◽  
Cyclic Hardening ◽  
Primary Objective ◽  
Static Recovery ◽  
Chaboche Model ◽  
Creep Fatigue ◽  
Grade 91

Chaboche unified viscoplasticity model and uncoupled plasticity and creep models (nonunified) are evaluated for their capability in simulating low-cycle fatigue, creep and creep-fatigue responses of Grade 91 steel. The primary objective of this study is to develop a constitutive model incorporating various advanced modeling features for design-by-analysis of elevated temperature power plant components. For validation of the model a broad set of experimental responses of Grade 91 in the temperature range 20–600°C are collected from literature. Performance of the models is demonstrated against simulating these experimental responses. It is demonstrated that the unified Chaboche model simulation capability can be improved through implementing strain range dependence, cyclic hardening through kinematic hardening rule and static recovery modeling features.

Improving Simulations for Low Cycle Fatigue and Ratcheting Responses of Elbows

2016 ◽  
Author(s):  
Nazrul Islam ◽  
Tasnim Hassan
Keyword(s):  
Residual Stresses ◽  
Low Cycle Fatigue ◽  
Numerical Technique ◽  
Kinematic Hardening ◽  
Model Development ◽  
Strain Range ◽  
Isotropic Hardening ◽  
Cycle Fatigue ◽  
Chaboche Model ◽  
Modeling Feature

A rate-independent constitutive model is developed incorporating various uniaxial and multiaxial modeling features for improving the simulations of elbow low-cycle fatigue and ratcheting responses. The model development is motivated by the fact that the Chaboche model in ANSYS is unable to simulate the strain ratcheting responses of elbows subjected to internal pressure and opening-closing displacement-controlled cycles. This drawback of the existing model is traced to the isotropic and kinematic hardening modeling features. The isotropic hardening in the Chaboche model can reasonably simulate the material test stress peaks but fails to simulate the hysteresis loop shapes. Incorporation of a strain range dependent modeling feature in evolving the isotropic and kinematic hardening rule parameters improved the simulation of the hysteresis loops both at the material and component levels. The axial and circumferential strain ratcheting simulation of elbow is improved by incorporating a biaxial ratcheting parameter. A modeling feature for nonproportional loading developed by Tanaka is also incorporated in order to simulate the additional cyclic hardening under multiaxial loading. The performance of modified model developed is validated against simulating a broad set of cyclic responses both at the material and component levels. Finally, a numerical technique is developed to simulate the initial and welding residual stresses in elbows, and thereby analytically demonstrate the influence of initial residual stresses on elbow responses.

Mean Stress Effect on Fatigue Properties of Type 316 Stainless Steel: Part I — In High-Temperature Air Environment

2017 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Fatigue Life ◽  
Stress Amplitude ◽  
Mouth Opening ◽  
Strain Range ◽  
Peak Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Crack Mouth ◽  
Mean Stress Effect ◽  
The Mean

The mean stress effect on the fatigue life of Type 316 stainless steel was investigated at 325°C in air. It was shown that the fatigue life was extended by applying the mean stress under the same stress amplitude. Increase in the maximum peak stress by applying the mean stress induced additional plastic strain and this hardened the material. The strain range of the hardened material was relatively small for the same stress amplitude, and this extended the fatigue life for a given stress amplitude. On the other hand, the fatigue life was shortened by the mean stress for the same strain range. The mean stress increased the effective strain range due to an increase in the minimum peak stress. Also, the mean stress induced ratcheting strain during the fatigue test and this accelerated crack mouth opening. The enhanced crack mouth opening accelerated the crack growth and shortened the fatigue life for a given strain range.

scholarly journals Characterization of Austenitic Stainless Steels with Regard to Environmentally Assisted Fatigue in Simulated Light Water Reactor Conditions

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 307
Author(s):  
Matthias Bruchhausen ◽  
Gintautas Dundulis ◽  
Alec McLennan ◽  
Sergio Arrieta ◽  
Tim Austin ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Power Plants ◽  
Research Effort ◽  
Hold Time ◽  
Strain Range ◽  
Austenitic Steels ◽  
Mean Strain

A substantial amount of research effort has been applied to the field of environmentally assisted fatigue (EAF) due to the requirement to account for the EAF behaviour of metals for existing and new build nuclear power plants. We present the results of the European project INcreasing Safety in NPPs by Covering Gaps in Environmental Fatigue Assessment (INCEFA-PLUS), during which the sensitivities of strain range, environment, surface roughness, mean strain and hold times, as well as their interactions on the fatigue life of austenitic steels has been characterized. The project included a test campaign, during which more than 250 fatigue tests were performed. The tests did not reveal a significant effect of mean strain or hold time on fatigue life. An empirical model describing the fatigue life as a function of strain rate, environment and surface roughness is developed. There is evidence for statistically significant interaction effects between surface roughness and the environment, as well as between surface roughness and strain range. However, their impact on fatigue life is so small that they are not practically relevant and can in most cases be neglected. Reducing the environmental impact on fatigue life by modifying the temperature or strain rate leads to an increase of the fatigue life in agreement with predictions based on NUREG/CR-6909. A limited sub-programme on the sensitivity of hold times at elevated temperature at zero force conditions and at elevated temperature did not show the beneficial effect on fatigue life found in another study.

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