Application of the Wilshire Stress-Rupture and Minimum-Creep-Strain-Rate Prediction Models for Alloy P91 in Tube, Plate and Pipe Form

2019 ◽  
Author(s):  
Jaime A. Cano ◽  
Calvin M. Stewart
Keyword(s):  
Strain Rate ◽  
Creep Strain ◽  
Stress Rupture ◽  
Creep Strain Rate ◽  
Tube Plate ◽  
Short Term ◽  
Design Life ◽  
Term Creep ◽  
Term Data

Abstract There exists a challenge in predicting the long-term creep of materials (3 105 hours) where 11+ years of continuous testing is required to physically collect creep data. As an alternative to physical testing, constitutive models are calibrated to short-term data (< 104 hours) and employed to extrapolate the long-term creep behavior. The Wilshire model was introduced to predict the stress-rupture and minimum-creep-strain-rate behavior of materials and the model is well-accepted due to the explicit description of stress- and temperature-dependence allowing predictions across isotherms and stress levels. There is an ongoing effort to determine how alloy form affects the long-term creep predictions of the Wilshire model. In this study, stress-rupture and minimum-creep-strain-rate predictions are generated for alloy P91 in tube, plate, and pipe form. Data is gathered from the National Institute of Materials Science (NIMS) material database for alloy P91 at multiple isotherms. Following the establish calibration method for the Wilshire model, post-audit validation is performed using short-term data from NIMS to vet the extrapolations accuracy of each form at different isotherms. The Wilshire model demonstrates successful extrapolative techniques for the stress-rupture and minimum-creep-strain-rate of tube, plate, and pipe forms across multiple isotherms. Overall the form with the highest extrapolative accuracy for both stress-rupture and minimum-creep-strain-rate is the plate and the lowest one is the pipe. Stress-rupture design maps are provided where stress and temperature are axes and rupture-time is in contour. The design maps can be applied to: (a) given the boundary conditions, determine the design life (b) given the design life, determine the acceptable range of a boundary conditions. The latter is more useful in turbomachinery design.

Prediction of Long Term Stress Rupture Data for 2124

2006 ◽  
Vol 519-521 ◽  
pp. 1041-1046 ◽  
Author(s):  
Brian Wilshire ◽  
H. Burt ◽  
N.P. Lavery
Keyword(s):  
Q Methodology ◽  
Fracture Behavior ◽  
Stress Rupture ◽  
Creep Data ◽  
Short Term ◽  
Rupture Data ◽  
Term Creep ◽  
Term Data ◽  
Short Term Creep

The standard power law approaches widely used to describe creep and creep fracture behavior have not led to theories capable of predicting long-term data. Similarly, traditional parametric methods for property rationalization also have limited predictive capabilities. In contrast, quantifying the shapes of short-term creep curves using the q methodology introduces several physically-meaningful procedures for creep data rationalization and prediction, which allow straightforward estimation of the 100,000 hour stress rupture values for the aluminum alloy, 2124.

Probabilistic Minimum-Creep-Strain-Rate and Stress-Rupture Prediction for the Long-Term Assessment of IGT Components

2020 ◽  
Author(s):  
Md Abir Hossain ◽  
Calvin M. Stewart
Keyword(s):  
Strain Rate ◽  
Creep Strain ◽  
Probabilistic Model ◽  
Stress Rupture ◽  
Service Condition ◽  
Creep Strain Rate ◽  
Experimental Uncertainty ◽  
Initial Damage ◽  
Long Duration

Abstract Time-dependent creep induced failure is a major concern for structural components (i.e. IGT components, Gen IV nuclear reactor components) operating at elevated temperature. The likelihood of a failure is aggravated by randomness in several sources of uncertainty. Creep rupture data shows expanding scatter bands for long-duration creep tests where uncertainty can span multiple logarithmic decades of life. This experimental uncertainty is exacerbated by the uncertainties that exist during service. The continuum damage mechanics (CDM) based creep-damage model readily available in literature does not consider the uncertainty effect while predicting the long-term reliability of the components; rather the problem is tackled deterministically. Introduction of probabilistic phenomena into the existing model to predict the minimum-creep-strain-rate (MCSR) and stress-rupture (SR) would present a pathway for estimation of effect of uncertainty ensuing high reliability in the assessment. The objective of this paper is to develop a probabilistic model for MCSR and SR that is capable of predicting experimental uncertainty and extrapolating the expanded scatter bands observed in long-duration creep data. The Sine-hyperbolic (Sinh) CDM model is selected. Multi-isotherm MCSR and SR data for 304 (18Cr-8Ni) and 316 (18Cr-12Ni-Mo) stainless steel are gathered from the NIMS material database. A deterministic calibration is performed where the optimal material constants are obtained with no initial damage and perfect loading conditions. Probabilistic calibration begins with adding ASTM-specified temperature and stress tolerances (± X°C, ±Y% MPa) to capture a portion of the experimental uncertainty. The initial damage tolerances is then calibrated to capture the remaining uncertainty in the data. Probability distribution functions (pdfs) are assigned to each uncertainty parameter. Monte Carlo simulations are performed over a range of stress and temperature. The probabilistic Sinh model is shown to predict the expanding scatter band observed in long-term MCSR and SR data. Parametric simulations are performed where service condition uncertainty is added to the probabilistic model. It is determined that service condition uncertainties further degrade the creep resistance of a material.

Study on Relationship Between Dislocation Density and Creep Strain Rate of Single Crystal Ni Based Superalloy for Gas Turbines Using the Discrete Cosine Transform

2021 ◽  
Author(s):  
Hideo Hiraguchi
Keyword(s):  
Dislocation Density ◽  
Strain Rate ◽  
Single Crystal ◽  
Creep Strain ◽  
Discrete Cosine Transform ◽  
Gas Turbines ◽  
Elevated Temperatures ◽  
Creep Strain Rate ◽  
Cosine Transform ◽  
Term Creep

Abstract The discrete cosine transform (DCT) is known to be able to express the relation curve between creep strain and time, or the relation curve between creep strain rate and time very well. Moreover, recently it has been found out that the DCT can draw electron density distribution maps of crystals. In addition, the DCT always passes through all the points measured at an equal interval in any continuous curves and its interpolated values between adjacent points are very reasonable. Furthermore, a new prediction method for long term creep curves from short term creep data by using the DCT was reported at TurboExpo2020. Up to the present, the strength of single crystal Nickel based superalloys for gas turbines at elevated temperatures has been advanced by controlling the interface dislocation density and the lattice misfit at the γ/γ’ interfaces. For this reason, it has to be understood how to evaluate a relationship between interface dislocation density and creep strain rate to develop more advanced single crystal Nickel based superalloys. Therefore, in this research it was studied how to evaluate the relationship between interface dislocation density and creep strain rate of a single crystal Nickel based superalloy for gas turbines by using the DCT. As a result, useful properties on the effective stress have been obtained from the coefficients of the DCT.

scholarly journals Accelerated Creep Test (ACT) Qualification of Creep-Resistance Using the WCS Constitutive Model and Stepped Isostress Method (SSM)

2021 ◽  
Author(s):  
Jaime A. Cano ◽  
Calvin M. Stewart
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Creep Strain ◽  
Creep Deformation ◽  
Inconel 718 ◽  
Creep Resistance ◽  
Stress Rupture ◽  
Creep Testing ◽  
Accelerated Creep

Abstract In this study, a qualification of accelerated creep-resistance of Inconel 718 is assessed using the novel Wilshire-Cano-Stewart (WCS) model and the stepped isostress method (SSM) and predictions are made to conventional creep data. Conventional creep testing (CCT) is a long-term continuous process, in fact, the ASME B&PV III requires that 10,000+ hours of experiments must be conducted to each heat for materials employed in boilers and/or pressure vessel components. This process is costly and not feasible for rapid development of new materials. As an alternative, accelerated creep testing techniques have been developed to reduce the time needed to characterize the creep resistance of materials. Most techniques are based upon the time-temperature-stress superposition principle (TTSSP) that predicts minimum-creep-strain-rate (MCSR) and stress-rupture behaviors but lack the ability to predict creep deformation and consider deformation mechanisms that occur for experiments of longer duration. The stepped isostress method (SSM) has been developed which enables the prediction of creep deformation response as well as reduce the time needed for qualification of materials. The SSM approach has been successful for polymer, polymeric composites, and recently has been introduced for metals. In this study, the WCS constitutive model, calibrated to SSM test data, qualifies the creep resistance of Inconel 718 at 750°C and predictions are compared to CCT data. The WCS model has proven to make long-term predictions for stress-rupture, minimum-creep-strain-rate (MCSR), creep deformation, and damage in metallic materials. The SSM varies stress levels after time interval adding damage to the material, which can be tracked by the WCS model. The SSM data is calibrated into the model and the WCS model generates realistic predictions of stress-rupture, MSCR, damage, and creep deformation. The calibrated material constants are used to generate predictions of stress-rupture and are post-audit validated using the National Institute of Material Science (NIMS) database. Similarly, the MCSR predictions are compared from previous studies. Finally the creep deformation predictions are compared with real data and is determined that the results are well in between the expected boundaries. Material characterization and mechanical properties can be determined at a faster rate and with a more cost-effective method. This is beneficial for multiple applications such as in additive manufacturing, composites, spacecraft, and Industrial Gas Turbines (IGT).

Acquisition and analysis of creep data

1994 ◽  
Vol 29 (3) ◽  
pp. 159-165 ◽  
Author(s):  
B Wilshire ◽  
R W Evans
Keyword(s):  
Stress Rupture ◽  
Creep Data ◽  
Short Term ◽  
Design Data ◽  
Factors Affecting ◽  
Term Creep ◽  
International Testing ◽  
Testing Standards ◽  
High Degree

The limitations of traditional methods of providing long-term creep design data are discussed in relation to existing national and international testing standards, current parametric procedures for extrapolation of stress-rupture values and the factors affecting the high degree of scatter in conventional long-term property sets for widely-used structural steels. These deficiencies may be overcome by adopting an alternative data acquisition methodology based on the analysis of short-term high-precision constant-stress creep curves.

Reliability Prediction of 304 Stainless Steel Using Sine-Hyperbolic Creep-Damage Model With Monte Carlo Simulation Method

2019 ◽  
Author(s):  
Md Abir Hossain ◽  
Calvin Maurice Stewart
Keyword(s):  
Stainless Steel ◽  
Monte Carlo ◽  
Strain Rate ◽  
Creep Strain ◽  
Creep Deformation ◽  
Stress Rupture ◽  
Material Constant ◽  
Creep Strain Rate ◽  
304 Stainless Steel ◽  
Material Constants

Abstract Typically continuum damage mechanics (CDM) based constitutive models are applied deterministically where the uncertainty of experiments is not considered. This is also true for the Sine-hyperbolic (Sinh) CDM-based constitutive model where the model is calibrated to represent 50% reliability of creep data. There is a need to implement Sinh in a more stochastic manner. The objectives of this study is to incorporate the probabilistic feature in the Sinh creep damage model to reliably predict the minimum-creep-strain-rate, creep-rupture and creep deformation. This will be achieved using Monte-Carlo methods. Creep deformation data for 304 Stainless Steel is collected from literature consisting of tests conducted at 300 and 320 MPa at 600°C with five replicates. The replicate tests exhibited substantial scatter in the minimum-creep-strain-rate, stress-rupture, and overall creep deformation. Subsequently, upon calibration using the Sinh model, the material constants among the replicates varied. The trends of uncertainty carried by each material constant are studied. The interdependence of the material constants is evaluated to determine if the uncertainty carried by each material constant can be regressed using a co-dependence function. The Monte Carlo method was applied to determine the extent that the creep deformation curve varies taking into consideration the variability of the material constants. Monte Carlo simulations show that the predicted creep deformation persists within the bounds of the experimental data. A large number of Monte Carlo simulations using the Sinh model enabled the creation of credible reliability bands for the minimum-creep-strain-rate, stress-rupture, and creep deformation of 304 Stainless Steel. In future work, this statistical method will be applied to the variability of service conditions, pre-existing defects, and material constants to quantitatively establish the reliability of the Sinh model in simulating component-level creep deformation to rupture.

Progress in Developing Constitutive Equations for Inelastic Design Analysis

1983 ◽  
Vol 105 (3) ◽  
pp. 273-276 ◽  
Author(s):  
C. E. Pugh
Keyword(s):  
Constitutive Equations ◽  
Inelastic Strain ◽  
Short Term ◽  
Inelastic Material ◽  
Fast Breeder Reactors ◽  
Breeder Reactors ◽  
Term Creep ◽  
Inelastic Design ◽  
Creep Deformations

A summary is given of the constitutive equations that have been developed for use in design assessments of elevated temperature components of liquid metal fast breeder reactors. The discussion addresses representations of short-term (plastic) and long-term (creep) inelastic material responses. Attention is given to improved representations of the interactions between plastic and creep deformations. Most of the discussion is in terms of constitutive equations that make use of the concept of separating the total strain into elastic, plastic, and creep portions. Additionally, some discussion is given of progress being made toward establishing design equations based on unified measures of inelastic strain that do not distinguish different strain portions.

Effects of ternary additions on the deformation behavior of single crystals of MoSi2

2000 ◽  
Vol 646 ◽  
Author(s):  
Haruyuki Inui ◽  
Koji Ishikawa ◽  
Masaharu Yamaguchi
Keyword(s):  
Yield Strength ◽  
Strain Rate ◽  
Single Crystals ◽  
Creep Strain ◽  
High Temperatures ◽  
Low Temperatures ◽  
Deformation Behavior ◽  
Creep Strain Rate ◽  
Compression Creep ◽  
Ternary Additions

ABSTRACTEffects of ternary additions on the deformation behavior of single crystals of MoSi2 with the hard [001] and soft [0 15 1] orientations have been investigated in compression and compression creep. The alloying elements studied include V, Cr, Nb and Al that form a C40 disilicide with Si and W and Re that form a C11b disilicide with Si. The addition of Al is found to decrease the yield strength of MoSi2 at all temperatures while the additions of V, Cr and Nb are found to decrease the yield strength at low temperatures and to increase the yield strength at high temperatures. In contrast, the additions of W and Re are found to increase the yield strength at all temperatures. The creep strain rate for the [001] orientation is significantly lower than that for the [0 15 1] orientation. The creep strain rate for both orientations is significantly improved by alloying with ternary elements such as Re and Nb.

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