A Microstructural Sensitivity Study of 316H Austenitic Stainless Steel to Inter-Granular Creep Fracture

2011 ◽  
Vol 488-489 ◽  
pp. 658-661
Author(s):  
B. Chen ◽  
Peter E.J. Flewitt ◽  
David John Smith ◽  
C.M. Younes
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Damage Model ◽  
Creep Damage ◽  
Longitudinal Section ◽  
Sensitivity Study ◽  
Assessment Procedure ◽  
Creep Failure ◽  
Creep Ductility ◽  
Damage Prediction

A preliminary sensitivity examination of the ductility exhaustion based creep damage prediction model, currently used in the R5 high temperature assessment procedure, showed that material property inputs had significant effects on damage prediction. In the present work, the link between the microstructural factors and the susceptibility to inter-granular high temperature creep failure is considered. The latter was judged to be associated with the low creep ductility. Here, the longitudinal section of a creep specimen and the fracture surface were examined. Auger electron spectroscopy was used to investigate the grain boundary composition in this specimen, which failed after a creep test of 1038h at 550°C under a triaxial stress state. The present results demonstrate that there is a possibility to correlate the susceptibility to high temperature inter-granular fracture from the low temperature fracture investigations. Finally, the susceptibility of the pre-treated 316H stainless steel to inter-granular high temperature failure and the contribution to the creep damage model are briefly discussed.

Creep Failure Simulations for 316H at 550°C

2012 ◽  
Author(s):  
Nak Hyun Kim ◽  
Yun Jae Kim ◽  
Catrin M. Davies ◽  
Kamran M. Nikbin ◽  
David W. Dean
Keyword(s):  
Experimental Data ◽  
Damage Model ◽  
Creep Damage ◽  
Inelastic Strain ◽  
Compact Tension ◽  
Creep Failure ◽  
Creep Ductility ◽  
Summation Rule ◽  
Creep Damage Model ◽  
Damage Summation

In this work a method to simulate failure due to creep is proposed using finite element damage analysis. The creep damage model is based on the creep ductility exhaustion concept. Incremental damage is defined by the ratio of incremental inelastic (plastic & creep) strain and multi-axial ductility. A simple linear damage summation rule is applied. When accumulated damage becomes unity, element stresses are reduced to almost zero to simulate progressive crack growth. The model is validated through comparison with experimental data on various sized compact tension, C(T), specimens of 316H stainless steel at 550 °C. The influence of the inelastic strain rate on the uniaxial ductility is considered. Good agreement is found between the simulated results and the experimental data.

An improved nonlinear damage model of rocks considering initial damage and damage evolution

2020 ◽  
Vol 29 (7) ◽  
pp. 1117-1137 ◽  
Author(s):  
Wenlin Feng ◽  
Chunsheng Qiao ◽  
Shuangjian Niu ◽  
Zhao Yang ◽  
Tan Wang
Keyword(s):  
Damage Evolution ◽  
Least Squares Method ◽  
Damage Model ◽  
Creep Damage ◽  
Secondary Creep ◽  
Nonlinear Creep ◽  
Creep Failure ◽  
Initial Damage ◽  
Nonlinear Damage Model ◽  
Creep Damage Model

The experimental results show that the creep properties of the rocks are affected by the initial damage, and the damage evolution also has a significant impact on the time-dependent properties of the rocks during the creep. However, the effects of the initial damage and the damage evolution are seldom considered in the current study of the rocks' creep models. In this paper, a new nonlinear creep damage model is proposed based on the multistage creep test results of the sandstones with different damage degrees. The new nonlinear creep damage model is improved based on the Nishihara model. The influences of the initial damage and the damage evolution on the components in the Nishihara model are considered. The creep damage model can not only describe the changes in three creep stages, namely, the primary creep, the secondary creep, and the tertiary creep, but also reflect the influence of the initial damage and the damage evolution on creep failure. The nonlinear least squares method is used to determine the parameters in the nonlinear creep damage model. The consistency between the experimental data and the predicted results indicates the applicability of the nonlinear damage model to accurately predict the creep deformation of the rocks with initial damage.

Study on Probabilistic Model of GH4133B for Fatigue-Creep Failure

2009 ◽  
Author(s):  
Dianyin Hu ◽  
Rongqiao Wang
Keyword(s):  
High Temperature ◽  
Reliability Analysis ◽  
Probabilistic Model ◽  
Low Cycle Fatigue ◽  
Limit State ◽  
Interactive Effect ◽  
Creep Damage ◽  
Sensitivity Index ◽  
State Function ◽  
Creep Failure

GH4133B is a nickel-base superalloy which was developed for use in the manufacture of aero-engine turbine disks and other high-temperature components. Since these components are operated at high temperature and under cyclic loading, damage resulting from fatigue-creep interaction is the main factor. The situation is often simulated in laboratories at high temperature low-cycle fatigue. The interactive effect between different loading levels should be considered. The fatigue-creep experiments for alloy GH4133B at 600 Celsius degree have been carried out at continuous cyclic creep (CF) loading to investigate the interaction of creep damage and fatigue damage. Fracture surfaces are examined under the scanning electron microscope (SEM). Then a nonlinear fatigue-creep failure criterion function proposed by Hongyin Mao is employed to fit the experimental data. The probabilistic model of GH4133B under CF loading is established based on the deterministic failure function. Firstly, the random variables influencing the fatigue-creep life and values of the distribution parameters are investigated. Then fatigue-creep damage interaction is discussed and a linear damage accumulation rule is considered, according to which the limit state function used to express the probability of failure is proposed. Lastly, reliability analysis under fatigue-creep failure is proceeded by applying analytical and simulation methods. Furthermore, the random variable with low sensitivity index through the sensitivity analysis can be treated as deterministic parameter during the reliability analysis and reliability design in order to improve the computing efficiency.

Probabilistic Creep Modeling of 304 Stainless Steel Using a Modified Wilshire Creep-Damage Model

2020 ◽  
Author(s):  
Md. Abir Hossain ◽  
Jaime A. Cano ◽  
Calvin M. Stewart
Keyword(s):  
Stainless Steel ◽  
Monte Carlo ◽  
Temperature Stress ◽  
Creep Deformation ◽  
Material Properties ◽  
Probabilistic Model ◽  
Damage Model ◽  
Creep Damage ◽  
304 Stainless Steel ◽  
Creep Damage Model

Abstract Pressure vessel components subject to high temperature and pressure are susceptible to life-limiting creep and/or creep-induced failure. Traditional continuum damage mechanics (CDM) based creep-damage model are used extensively for the prediction and design against creep in these components. Conventional creep experiments show considerable uncertainty in the creep response of materials where scatter can span decades of creep life. The objective of this paper is to introduce the probabilistic methods into a deterministic creep-damage model in order to predict experimental uncertainty. In this study, a modified Wilshire model capable of creep deformation, damage, and rupture prediction is selected. Creep deformation data for 304 stainless steel is collected from the literature consisting of quintuplicate (five) tests at 600°C with varying stress levels. It is hypothesized that the scatter in creep data is due to: test condition (temperature fluctuations and eccentric loading), initial damage (pre-existing surface and sub-surface defects), and metallurgical (local variation in microstructure) uncertainties. Probability distribution functions (pdfs) and Monte Carlo simulations are applied to introduce the uncertainties into the modified Wilshire equations. The domain of each source of uncertainty must be defined. A systematic calibration approach is followed where the material constant for each creep curve (in the quintuple) are obtained and statistical analysis is performed on the material properties to assess the random distribution associated with each uncertain material parameter. The probabilistic calibration begins with the introduction of test condition randomness (±2°C and ±3.2% MPa of nominal temperature/stress) in accordance with the ASTM standards. Cross calibration of temperature-stress variability proceeds the approximation of initial damage uncertainty which captures the remaining scatter in the data. Deterministic calibration unveils the range of variabilities associated with the material properties. The best-fitted pdfs are assigned to each uncertain parameter and subsequently, the deterministic model is converted into a probabilistic model where reliability is a tunable factor. A large number of Monte Carlo simulation are conducted to generate probabilistic creep deformation, minimum-creep-strain-rate (MCSR), and stress-rupture (SR) predictions. It is demonstrated that the probabilistic model produces quantitatively and qualitatively good fits when compared with experimental data. Future work will be directed towards the inclusion of service condition related uncertainty (power plant, turbine blade, Gen IV nuclear reactor application) into the probabilistic framework where the uncertainties are more robust.

Some Fundamental Aspects of High Temperature Defect Assessment

2005 ◽  
Vol 297-300 ◽  
pp. 428-434 ◽  
Author(s):  
Shan Tung Tu ◽  
Fu Zhen Xuan
Keyword(s):  
High Temperature ◽  
Assessment Method ◽  
Damage Effect ◽  
Assessment Procedure ◽  
Continuum Damage ◽  
Creep Failure ◽  
Failure Assessment Diagram ◽  
Defect Assessment ◽  
Failure Assessment ◽  
Dependent Failure

Current research efforts in the development of high temperature defect assessment procedure are summarized. Creep exemption criteria are proposed for the assessment of defective structures at high temperature in consideration of the effects of loadings, operating temperature and service time. Time-dependent failure assessment diagram (TDFAD) is developed that covers major failure mechanisms of defective high temperature structures. Challenges due to the welding effect are discussed. TDFAD for weldments is derived for various combinations of materials. In order to develop a unified assessment method to cope with material and loading complexity, a new failure assessment diagram based on continuum damage concept is proposed to reflect the damage effect on ductile creep failure and brittle creep fracture.

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.

scholarly journals Thermomechanical fatigue behaviour of ferritic stainless steel grades for high temperatures applications

2018 ◽  
Vol 165 ◽  
pp. 16003
Author(s):  
Cloé Prudhomme ◽  
Pierre-Olivier Santacreu ◽  
Isabelle Evenepoel ◽  
Benoit Proult
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
High Temperatures ◽  
Thermal Loading ◽  
Low Cycle Fatigue ◽  
Damage Model ◽  
Thermomechanical Fatigue ◽  
Compression Tests ◽  
Wide Range ◽  
Steel Grades

Nowadays high temperatures resistant materials are needed to resist to high temperature applications (up to 1000°C), such as automotive exhaust gas manifolds. Some developed stainless steel grades, including ferritic grades or austenitic refractory grades, can be used in this temperature range and both in continuous or cyclic thermal conditions. In order to predict the thermomechanical fatigue damage of stainless steel parts submitted to cyclic thermal loading and constrained bonding conditions, the elastoviscoplastic model by Chaboche is determined for a wide range of temperatures, of strain amplitudes and strain rate levels thanks to isothermal traction-compression tests. The validation procedure is performed afterward by comparison with stabilized behavior under non isothermal conditions on a dedicated thermal fatigue test performed on V-shape specimens. Results of simulation show very good fitting with the experimental curves which would lead to a more accurate fatigue life prediction. A damage model was derived from Taira’s thermal low-cycle fatigue model to include dwell-time period at high temperature and creep-oxidation effect. In this paper the example of K44X, a dedicated grade for high temperatures applications, is presented.

Comparison Between Strain-Based and Energy-Based Creep Failure Simulation

2018 ◽  
Author(s):  
Seung Jae Kim ◽  
Young Ryun Oh ◽  
Yun Jae Kim
Keyword(s):  
High Temperature ◽  
Power Plant ◽  
Tensile Test ◽  
High Efficiency ◽  
Low Cycle Fatigue ◽  
Damage Model ◽  
Prediction Method ◽  
Life Time ◽  
Failure Model ◽  
Creep Failure

The power plant is required to operate under high temperature and pressure for high efficiency. In order to predict reliable life time of power plant under high temperature, creep-low cycle fatigue life prediction method should be proposed. In this paper, strain based and energy based failure model are proposed to simulate notch bar creep tensile test. Modification factors considering multiaxial fracture and strain rate effect were proposed in order to simulate notch bar creep tensile test using FE analysis. Using proposed models, FE result of strain based and energy based damage model are compared with notch bar creep tensile test. As a result, both strain and energy based damage model simulates crack growth well during creep, However, when tertiary creep behavior is considered, energy based failure model simulate rupture time longer than strain based model. It can be inferred that plastic damage accumulation of energy based model is slower than that of strain based model.

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