Effects of Creep Deformation Model of Gr. 91 Steel at 600°C on Creep Fracture Mechanics Parameters

2017 ◽  
Author(s):  
Min-Gu Won ◽  
Nam-Su Huh ◽  
Hyeong-Yeon Lee ◽  
Woo-Gon Kim ◽  
Jae-Boong Choi
Keyword(s):  
Finite Element ◽  
Fracture Mechanics ◽  
Creep Deformation ◽  
Creep Model ◽  
Deformation Model ◽  
Secondary Creep ◽  
Creep Fracture ◽  
Reference Stress ◽  
Creep Region ◽  
Omega Model

The present paper investigates the effect of creep deformation model of Gr. 91 Steel at 600 °C on creep fracture mechanics parameters. Three types of creep deformation model were considered, i.e. Garofalo’s model and RCC-MRx model for primary-secondary creep region, and modified omega model for primary-secondary-tertiary creep region. The parameters for each creep deformation model were characterized from experiment results. Reference Stress (RS) method was used to estimate creep fracture mechanics parameters, C(t)-integral and COD rate for each creep model. Furthermore, elastic-creep finite element (FE) analyses were carried out to verify the results of RS method. Finally, the effect of creep deformation model was investigated by comparing the results of C(t)-integral and COD rate.

Finite Element Simulation of Creep Deformation for Gr. 91 Steel at 600 °C Using Garofalo Model

2016 ◽  
Author(s):  
Min-Gu Won ◽  
Jae-Boong Choi ◽  
Nam-Su Huh ◽  
Hyeong-Yeon Lee ◽  
Woo-Gon Kim
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Creep Deformation ◽  
Creep Model ◽  
Deformation Model ◽  
Secondary Creep ◽  
Experiment Data ◽  
Element Simulation ◽  
Commercial Code ◽  
Creep Models

The present paper provides predictive creep deformation model for Gr. 91 steel at 600 °C. To cover primary-secondary creep regions, two types of creep models, i.e. Garofalo’s and RCC-MRx models were considered in the present study, where the parameters of Garofalo’s model were characterized based on experiment results, and the parameters of RCC-MRx model were determined by the values given in the RCC-MRx code. Furthermore, each creep model were developed based on CREEP (user creep subroutine invoked in ABAQUS) codes for applying to finite element (FE) simulations using commercial code. Then, FE analyses for creep deformation were performed by using the developed CREEP codes (for Garofalo’s and RCC-MRx models), and the results were compared with experiment data. As results, Garofalo’s model provides more accurate results than RCC-MRx model.

Research on Creep Fracture Mechanics Parameter by Reference Stress Method

2011 ◽  
Vol 189-193 ◽  
pp. 4383-4386
Author(s):  
Zhao Ji Hu ◽  
Ting Zhang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Fracture Mechanics ◽  
Creep Crack Growth ◽  
Element Analysis ◽  
Creep Fracture ◽  
Creep Crack ◽  
Creep Coefficient ◽  
Reference Stress ◽  
Power Law Creep

Creep fracture mechanics parameter C* is used to relate the data of Creep crack initiation (CCI) and Creep crack growth (CCG). Reference stress method (RSM) can be used to explain the result of finite element analysis on evaluating structures, and it is widely used to design and assess of general structures. The result of C* is affected by the creep coefficient A and creep exponent n for power-law creep in solving creep fracture mechanics parameter C* though using RSM.

Development of a Constitutive Backstress Model for the Prediction of Creep and Stress Relaxation in Gas Turbine Materials

2020 ◽  
Author(s):  
Andrew Moffat ◽  
Richard Green ◽  
Calum Ferguson ◽  
Brent Scaletta
Keyword(s):  
Stress Relaxation ◽  
Creep Deformation ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Creep Model ◽  
Effect Of Temperature ◽  
Deformation Model ◽  
Corrosion Resistant ◽  
Single Temperature ◽  
Wide Range

Abstract There is a drive towards a broader range of fuels in industrial gas turbines, with higher levels of sulphur and potentially hydrogen. Due to these harsher environments, there is also a drive for corrosion resistant alloys and coatings. A number of key corrosion resistant superalloys, which are being employed to cope with these evolving conditions, exhibit primary creep. It is therefore imperative that fundamental material models, such as those for creep deformation, are developed to ensure they can accurately predict the material response to evolving operating conditions. The requirements for a creep model are complex. The model must be able to: predict forward creep deformation in regions dominated by primary loads (such as pressure); predict stress relaxation in regions dominated by secondary loads (such as differential thermal expansion); predict the effects of different creep hardening mechanisms. It is also clear that there is an interaction between fatigue and creep. With flexible operation, this interaction can be significant and should be catered for in lifing methods. A model that has the potential to account for the effect of plasticity on creep, and creep on plasticity is therefore desirable. In previous work the authors presented the concept for a backstress model to predict creep strain rates in superalloys. This model was fitted to a limited dataset at a single temperature. The approach was validated using simple creep-dwell tests at the same temperature. This paper expands on the previous work in several ways: 1) The creep model has been fitted over a wide range of temperatures. Including the effect of temperature in complex creep models presents a number of difficulties in model fitting and these are explored. 2) The model was fitted to constant load (forward creep) and constant strain (stress relaxation) tests since any creep model should be able to predict both forms of creep deformation. However, these are often considered separately due to the difficulty of fitting models to two different datasets. 3) The creep deformation model was validated on stress change tests to ensure the creep deformation response can cope with changes in response variables. 4) The approach was validated using creep-fatigue tests to show that the creep deformation model, in addition to our established fatigue models, can predict damage in materials under complex loading.

Development of the RCC-MR Creep Deformation Model for the Prediction of Creep and Stress Relaxation in Type 321 Stainless Steel

2014 ◽  
Author(s):  
A. J. Moffat ◽  
J. P. Douglas ◽  
M. White ◽  
M. W. Spindler ◽  
C. Austin ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Stress Relaxation ◽  
Creep Strain ◽  
Creep Deformation ◽  
Constant Load ◽  
Fatigue Tests ◽  
Creep Model ◽  
Deformation Model ◽  
Relaxation Data ◽  
Creep And Stress Relaxation

In this paper a creep deformation model has been developed for Type 321 stainless steel which has been based on a modified version of the creep model that is used in the French fast reactor design code RCC-MR. The model has been evaluated using: 1) constant load creep data covering the temperature range from 550°C to 650°C and 2) constant displacement, stress relaxation data obtained from creep-fatigue tests at 650°C. Samples in the heat-treatment conditions of solution-treated, aged, and simulated ‘heat affected zone’ have been assessed. The standard RCC-MR model was fitted to the constant load data and provided good predictions of forward creep. However, when this model was used to predict stress relaxation it was observed that the model significantly over predicted creep strain rates and therefore the level of stress drop during each cycle. During constant load tests the stress remains relatively constant (noting that true stress does increase a small amount prior to rupture). However, in relaxation tests the stress varies significantly over the dwell. Due to the poor predictions of stress relaxation it was hypothesised that the fitted model did not capture the stress dependence of creep appropriately. The RCC-MR model was therefore modified to include a primary and secondary threshold stress term that is a function of the accumulated creep strain. This work indicates that the RCC-MR model, modified to include threshold stresses, can be used to provide good predictions of both forward creep and stress relaxation in Type 321 stainless steel. Further work is required to validate this model on stress relaxation data at additional temperatures and lower start of dwell stresses.

Creep Parameters Determination by Omega Model to Norton Bailey Law by Regression Analysis for Austenitic Steel SS-304

2021 ◽  
Vol 324 ◽  
pp. 188-197
Author(s):  
Mohsin Sattar ◽  
A. Rahim Othman ◽  
Shahrul Kamaruddin ◽  
Mohammad Azad Alam ◽  
Mohammad Azeem
Keyword(s):  
Regression Analysis ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Complete Analysis ◽  
Mechanical Equipment ◽  
Strain Rates ◽  
Secondary Creep ◽  
Creep Data ◽  
Ss 304 ◽  
Omega Model

In the material’s creep failure analysis, the difficulty of assessing the applied thermo-mechanical boundary conditions makes it critically important. Numerous creep laws have been established over the years to predict the creep deformation, damage evolution and rupture of the materials subjected to creep phenomena. The omega model developed by the American Petroleum Institute and Material Properties Council is one of the most commonly used creep material models for numerical analysis over the years. It is good in defining the fitness of mechanical equipment for service engineering evaluation to ensure the reliable service life of the equipment. The Omega model, however, is not readily accessible and specifically incorporated for creep evaluation in FEA software codes and creep data is always scarce for the complete analysis. Therefore, extrapolation of creep behavior was performed by fitting various types of creep models with a limited amount of creep data and then simulating them, beyond the available data points. In conjunction with the Norton Bailey model, based on API-579/ASME FFS-1 standards, a curve fitting technique was employed called regression analysis. From the MPC project omega model, different creep strain rates were obtained based on material, stress and temperature-dependent data. In addition, as the strain rates increased exponentially with the increase in stresses, regression analysis was used for predicting creep parameters, that can curve fit the data into the embedded Norton Bailey model. The uncertainties in extrapolations and material constants has highlighted to necessitate conservative safety factors for design requirement. In this case study, FEA creep assessment was performed on the material SS-304 dog bone specimen, considered as a material coupon to predict time-dependent plastic deformation along with creep behavior at elevated temperatures and under constant stresses. The results indicated that the specimen underwent secondary creep deformation for most of the period.

Creep behaviour of a buffer material for nuclear fuel waste vault

1985 ◽  
Vol 22 (4) ◽  
pp. 541-550 ◽  
Author(s):  
Raymond N. Yong ◽  
Prapote Boonsinsuk ◽  
Demos Yiotis
Keyword(s):  
Finite Element ◽  
Nuclear Fuel ◽  
Host Rock ◽  
Creep Behaviour ◽  
Creep Model ◽  
Secondary Creep ◽  
Full Size ◽  
Waste Container ◽  
Buffer Material ◽  
Nuclear Fuel Waste

In the Canadian nuclear fuel waste disposal concept currently under study, one of the prime candidate procedures is the borehole emplacement technique. Each fuel waste container will be placed in a 1.1 m diameter hole in the floor of a disposal vault in deep plutonic rock. The container will be surrounded by buffer material consisting of a mixture of clay and sand. This study examines the creep behaviour of the buffer material in the borehole during interaction with the waste container and the host rock. It simulated the buffer – container – host rock interaction through a small-scale physical model using the loading pressures anticipated in the full-size system. The results from the model tests were compared with those predicted by a finite element analytical model. The creep behaviour of the full-size system was then predicted using the analytical model.From the results, it is evident that the creep behaviour of the buffer material depends significantly on interaction within the container – buffer – host rock system, overburden pressure, and water uptake. At relatively low overburden pressures, the waste container might settle, causing a separation between the buffer material and the container top. However, this could be alleviated by the swelling properties of the buffer material. The secondary creep rates are negligible, and creep in the buffer material is primarily governed by the primary creep stage. Key words: creep, model test, swelling soil, soil deformation, unsaturated soil, finite element analysis.

Approximate J Estimates for Circumferential Cracks in between Elbows and Attached Pipes

2007 ◽  
Vol 345-346 ◽  
pp. 521-524
Author(s):  
Tae Kwang Song ◽  
Chang Kyun Oh ◽  
Yun Jae Kim ◽  
Jong Sung Kim ◽  
Tae Eun Jin
Keyword(s):  
Finite Element ◽  
Fracture Mechanics ◽  
Closed Form ◽  
Limit Load ◽  
Small Strain ◽  
Straight Pipe ◽  
Popular Approach ◽  
Elastic Plastic ◽  
Reference Stress ◽  
Mechanics Analysis

The present work proposes a method for elastic-plastic fracture mechanics analysis of the circumferential through-wall crack in between elbows and attached straight pipes, subject to in-plane bending. Based on small strain finite element limit analyses, closed-form limit load solutions are given first. Then applicability of the reference stress based method to approximately estimate J is proposed. One interesting finding is that a popular approach to assume that the crack locates in the straight pipe could lead to significantly different assessment results.

Creep Study for Fatigue Life Assessment of Two Lead-Free High Temperature Solder Alloys

1996 ◽  
Vol 445 ◽  
Author(s):  
J. Liang ◽  
P. S. Lee ◽  
N. Gollhardt ◽  
S. Schroeder ◽  
W. Morris
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Creep Deformation ◽  
Failure Criteria ◽  
Life Assessment ◽  
Lead Free ◽  
Creep Model ◽  
Secondary Creep ◽  
Solder Alloys ◽  
High Temperature Solder

AbstractCreep of two lead-free high temperature solder alloys, 95Sn-5Ag and 99Sn-1.0Cu was studied in this investigation. Room and high temperature creep tests were performed to examine deformation mechanisms and to establish mathematical models of creep deformation for the alloys. A state variable creep model was introduced to model both primary and secondary creep deformation of these two alloys which show a very significant primary creep. Fatigue life models of the alloys were established based on an energy-based failure criteria, which was deduced from variable strain amplitude tests at a constant strain rate of 0.003/sec, and from variable strain rates tests with two constant strain amplitudes of 0.005 and 0.01. Applications of the creep model includes determination of peak loads and hysteresis strain energy density in strain-controlled fatigue tests. It is demonstrated that the creep model can be very helpful to establish fatigue failure criteria and to assess fatigue lives of these two alloys.

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