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.

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 an Advanced Creep Model for Type 316 Stainless Steel

2007 ◽  
Author(s):  
J. Douglas ◽  
M. Spindler ◽  
R. Dennis
Keyword(s):  
Stainless Steel ◽  
Stress Relaxation ◽  
Creep Deformation ◽  
Stress Component ◽  
Primary Creep ◽  
Creep Model ◽  
Relaxation Behaviour ◽  
Loading History ◽  
Creep Data ◽  
Relaxation Equation

Methods for predicting stress relaxation behaviour rely on either the integration of a forward creep equation derived from constant load creep data or a stress relaxation equation specifically derived from data measured during dwell periods in either monotonic or cyclic loading. In general, these methods do not explicitly address the effects of prior loading history on the observed relaxation behaviour. In the current work, forward creep data have been acquired to allow identification of a stress-temperature dependent function that represents the observed correlation between measured values of primary creep strain and the initial plastic loading strain. The prediction of stress relaxation from forward creep equations has been extended to investigate the effects of plasticity on creep deformation through the inclusion of a back stress component in the creep deformation equations. The work is based on British Energy’s evolving experimental database for Type 316H stainless steel which includes data from ongoing low stress and stress change creep tests. These tests are currently being conducted to improve the understanding of plasticity-creep interaction effects. Improved methods for predicting stress relaxation in Type 316H stainless steel based on these experimental data are assessed against their ability to adequately describe the influence of prior loading history on primary creep and stress relaxation behaviour.

The stress relaxation and creep behaviour of a manganese-stabilized austenitic stainless steel

2009 ◽  
Vol 44 (3) ◽  
pp. 201-209 ◽  
Author(s):  
A Pagliarello ◽  
J Beddoes
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Stress Relaxation ◽  
Creep Strain ◽  
Creep Behaviour ◽  
Constant Load ◽  
Relaxation Behaviour ◽  
Creep Tests ◽  
Stress Strain ◽  
The Difference

The stress relaxation behaviour of 21–4N, a manganese-stabilized austenitic stainless steel, is investigated in terms of the metallurgical state, the application of multiple strain levels during ‘stepped’ stress relaxation testing at 700 °C, the strain level during isostrain stress relaxation tests at 538 °C and 700 °C, and the correspondence with results from constant-load creep tests. The results indicate that for isostrain stress relaxation tests the stress relaxation rate is similar for strains that span both elastic and plastic strain levels. A transition in the stress relaxation behaviour occurs at a stress level approximately equivalent to the tensile stress–strain proportional limit; below this transition the stress–strain rate relationship, or the time predicted for 1 per cent creep strain, obeys a creep power law type of equation. Stress relaxation testing successfully delineates the difference between the creep resistances of two different metallurgical conditions with similar tensile properties using fewer specimens and requiring less time. The time to 1 per cent creep strain determined from the analysis of stress relaxation results is always less than the actual time to 1 per cent creep strain during constant-load creep tests.

The Influence of Creep Strain Rate on Creep Damage Formation in Austenitic Stainless Steel

2018 ◽  
Author(s):  
Edward Hares ◽  
Mahmoud Mostafavi ◽  
Richard Bradford ◽  
Chris Truman
Keyword(s):  
Stainless Steel ◽  
Stress Relaxation ◽  
Creep Strain ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Operating Conditions ◽  
Element Analysis ◽  
Creep Ductility ◽  
User Subroutine ◽  
Lower Test

Motivated by the need to more accurately account for real, in-service, operating conditions, this paper aims to investigate whether creep strain accumulated at different strain rates is equally damaging. Previous research has suggested that creep strain is more damaging when accumulated more slowly in creep of notched bars. The research presented here seeks to address this question by considering the accumulation of creep strain during stress relaxation of notched bars. Repeat stress relaxation tests with varying dwell lengths were conducted so that the relative damaging effects of the early, rapid accumulation and later, slow accumulation of creep strains could be compared. Another aim was to determine how a lower test temperature affects this creep strain accumulation. In repeat relaxation tests the load is reestablished repeatedly after relaxation dwells of equal duration, until rupture of the specimen occurs. The material used was an ex-service powerplant stainless steel Type 316H. Notched bar specimens were used to introduce stress triaxiality at the notch tip to imitate the multiaxial loads plant components are subjected to during in-service operation. The stresses and strains in the specimens were then assessed using finite element analysis; a user subroutine was implemented so the onset and propagation of creep damage could be simulated throughout the specimens’ creep life. The research found that the material in question had a lower creep ductility at 515°C than at 550°C. The research also showed that creep strain accumulated rapidly at the start of a dwell is significantly less damaging than creep strain accumulated more slowly towards the end of the dwell.

Creep Deformation of 20 Percent Cold Worked Type 316 Stainless Steel

1977 ◽  
Vol 99 (2) ◽  
pp. 168-180 ◽  
Author(s):  
E. R. Gilbert ◽  
L. D. Blackburn
Keyword(s):  
Stainless Steel ◽  
Creep Strain ◽  
Creep Deformation ◽  
Stress Conditions ◽  
Constant Stress ◽  
Experimental Results ◽  
Temperature Dependent ◽  
316 Stainless Steel ◽  
Stress Levels ◽  
Cold Worked

Creep deformation of internally pressurized tube specimens of 20 percent cold worked Type 316 stainless steel was measured under isothermal, constant stress conditions. Stress levels varied from zero to as high as 413 MPa (60,000 psi) for tests at five temperatures over the range from 714 K (825°F) to 1033 K (1400°F) for times to 3.6 × 106 seconds (2410 hours). Experimental results were represented by an equation of the form εc=Aσcosh−1(1+rt)+Pσntm+Qσnt2.5 where εc is the creep strain, σ is the stress, t is time, and the remaining quantities are temperature dependent parameters.

Fatigue and SCC Behavior of Sensitized SUS304 Stainless Steel in Pressurized Hot Water at 7.3MPa and 288°C

2011 ◽  
Vol 399-401 ◽  
pp. 2276-2282 ◽  
Author(s):  
Anchalee Saengsai ◽  
Yuichi Otsuka ◽  
Yoshiharu Mutoh
Keyword(s):  
Stainless Steel ◽  
Threshold Stress ◽  
Constant Load ◽  
Fatigue Tests ◽  
Hot Water ◽  
Mean Stress ◽  
Threshold Stress Intensity ◽  
Sus304 Stainless Steel ◽  
R Ratio ◽  
Threshold Stress Intensity Factor

Plain fatigue and fretting fatigue tests of sensitized SUS304 stainless steel under pressurized hot water at 7.3MPa and 288°C have been carried out. Fatigue strengths for both fatigue tests almost coincided. Fretting contact could nucleate small SCC cracks near the contact edge in the direction perpendicular to cyclic loading. High R–ratio reduced fatigue strength due to longer exposure time to corrosive environment at high mean stress. From the constant load SCC tests of the specimen with small SCC pre–crack induced by fretting contact, it was found that the threshold stress intensity factor for growth of small SCC precrack was 4.1MPa·m1/2, which was significantly lower than that for long crack (10MPa·m1/2).

The Visco-Elastic Behaviors of PVC Coated Fabrics under Different Stress and Temperatures

2010 ◽  
Vol 168-170 ◽  
pp. 1476-1479 ◽  
Author(s):  
Ying Ying Zhang ◽  
Qi Lin Zhang ◽  
Chuan Zhi Zhou
Keyword(s):  
Stress Relaxation ◽  
Initial Stress ◽  
Creep Strain ◽  
Elastic Strain ◽  
Membrane Structure ◽  
Initial Stresses ◽  
Under Five ◽  
Creep And Stress Relaxation ◽  
Coated Fabrics

The visco-elastic behaviors of coated fabrics are important for the design of membrane structure. In this paper, Ferrari 1002 is taken as the research object. The tests of creep and stress relaxation are carried out under five temperatures (23, 40, 50, 60, and 70 ) and three initial stresses (4, 15, and 26 kN/m), respectively. Results show that temperature and initial stress has great effects on the visco-elasticity of coated fabrics. With temperature and initial stress increasing, the visco-elastic behaviors are more obvious. The creep strain can be ignored compared with the corresponding elastic strain. After 24h, the remaining stress is less than 80% the initial stress. This paper can be references for the design of membrane structure.

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