On the Determination of Material Creep Constants Using Miniature Creep Test Specimens

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Tom H. Hyde ◽  
Balhassn S. M. Ali ◽  
Wei Sun
Keyword(s):  
Creep Test ◽  
Test Specimen ◽  
Creep Damage ◽  
Creep Model ◽  
P91 Steel ◽  
Notched Specimen ◽  
Material Constants ◽  
Damage Models ◽  
Uniaxial Creep ◽  
Material Creep

Full size creep test specimens, i.e., conventional uniaxial creep test specimen and Bridgman notch specimens are usually used to determine the full set of material constants for any creep model. However, in many situations, sufficient material is not available for theses specimens to be manufactured from it. Therefore, small creep test specimens have been introduced and used to determine (i) creep constants and (ii) the remaining life time for engineering components. Two commonly used small creep specimen types, i.e., the impression and the small ring creep tests, are used in this paper to determine the steady state creep constants. However, these specimen types are limited for use in determining the secondary creep properties, i.e., they are unable to determine the full set of material creep constants for creep damage models. In this paper the recently developed small two-bar creep test specimen and the newly developed small notched specimen test are described and used to determine a full set of material constants for Kachanov and Liu-Murakami creep damage models. The small notched specimen manufacturing, loading and testing procedures are described in this paper. P91 steel at 600 °C and (Bar-257) P91 steel at 650 °C have been used to compare the material constants obtained from the small two-bar and the small notched creep test specimens with those obtained from the conventional uniaxial creep test specimens and Bridgman notch specimens. The results show remarkably good agreement between the two sets of results.

Determination of Material Constants for Creep Damage Models Using Small Two-Bar and Notched Specimens

2014 ◽  
Author(s):  
Balhassn S. M. Ali ◽  
Thomas H. Hyde ◽  
Wei Sun
Keyword(s):  
Strain Rate ◽  
Creep Strain ◽  
Creep Test ◽  
Creep Damage ◽  
Creep Strain Rate ◽  
Creep Testing ◽  
Small Specimen ◽  
Material Constants ◽  
Damage Models ◽  
Testing Techniques

The work presented in this paper forms part of the research related to the development of small specimen creep testing techniques, which can be used when only small volumes of materials are available. Commonly used small creep test specimen types such as the impression and small ring creep tests can be only used to determine the minimum creep strain rate data. In this paper, two novel small-sized creep test specimens are described: (i) the recently developed small two-bar specimen, which is suitable for use in obtaining both uniaxial creep strain rate and creep rupture life data, and (ii) the newly developed small notched specimen, which can be used to determine the multiaxial stress state parameter. The two specimen types have been used to determine a full set of material constants for Norton model, Kachanov and Liu-Murakami creep damage models. Conversion relationships have been obtained based on the reference stress method in conjunction with the finite elements analyses and have been used to convert the two-bar specimen data to the corresponding uniaxial data. Two P91 power plant steels have been used to assess the accuracy of the two testing methods, (i) a weak P91 (Bar-257) steel at 650°C and (ii) a normal P91 (as received) steel at 600°C. The correlation between the data obtained from the two small specimens testing techniques and the corresponding uniaxial and Bridgeman specimens tests is excellent. The major advantages of the two novel small specimens testing techniques, over some existing small specimen creep testing techniques, are also highlighted in this paper.

Modeling the Creep Damage of P91 Steel Using Peridynamics

2019 ◽  
Author(s):  
Shank S. Kulkarni ◽  
Alireza Tabarraei ◽  
Xiaonan Wang
Keyword(s):  
Experimental Data ◽  
High Temperature ◽  
Structural Integrity ◽  
Creep Damage ◽  
Creep Model ◽  
Creep Tests ◽  
P91 Steel ◽  
Damage Models ◽  
Modeling Creep ◽  
Non Local

Abstract Creep is an important failure mechanism of metal components working at a high temperature. To ensure the structural integrity and safety of systems working at high temperature it is essential to predict failure due to creep. Classical continuum based damage models are used widely for modeling creep damage. A more recently developed non-local mechanics formulation called peridynamics has displayed better performance in modeling damage with respect to classical local mechanics methods. In this paper, the peridynamic formulation is extended to model creep in metals. We have chosen Liu-Murakami creep model for developing a peridynamic formulation for modeling creep. The proposed formulation is validated by simulating creep tests for P91 steel and comparing the results with experimental data from the literature.

Creep performance of OFP copper for the overpack of repository canisters

2006 ◽  
Vol 932 ◽  
Author(s):  
Pertti Auerkari ◽  
Stefan Holmström ◽  
Jorma Salonen ◽  
Pertti Nenonen
Keyword(s):  
Grain Boundary ◽  
Axial Stress ◽  
Creep Damage ◽  
Parent Material ◽  
Creep Model ◽  
Boundary Zone ◽  
Creep Failure ◽  
Uniaxial Creep ◽  
Notch Tip

ABSTRACTTo experimentally assess the long term creep performance of oxygen-free phosphorus- doped (OFP) copper for the overpack of repository canisters, the combination of modestly elevated temperature and multi-axial stress state has been applied for accelerated testing. Multi-axiality was induced by using notched compact tension (CT) specimens, with interrupted testing to periodically inspect for creep damage. Uniaxial creep testing was also conducted to support creep analysis of the CT specimens. After about 10000 h of testing at 150°C/46 MPa (reference stress), the inspected CT specimens showed only marginal creep cavity indications near the notch tip. However, a distinct grain boundary zone with elevated Pcontent was observed to appear and widen during testing, mainly near the notch tip. The significance of the grain boundary zone is not well understood, but indicates stress-enhanced microstructural changes at relatively low temperatures. The predicted isothermal uniaxial creep life at 150°C/46 MPa agreed satisfactorily within a factor of two in time, when obtained independently from converted multi-axial testing results and directly from a creep model based on the available uniaxial data. Although the uncertainties in extended extrapolation remain large, the prediction would suggest safe long term service at leastagainst pure creep failure of intact parent material.

scholarly journals Small Two-Bar Specimen Creep Testing of Grade P91 Steel at 650°C

2016 ◽  
Vol 35 (3) ◽  
pp. 243-252
Author(s):  
Balhassn S. M. Ali ◽  
Tom H. Hyde ◽  
Wei Sun
Keyword(s):  
Strain Rate ◽  
Creep Strain ◽  
Test Data ◽  
Creep Test ◽  
Uniaxial Stress ◽  
Creep Rupture ◽  
Creep Strain Rate ◽  
P91 Steel ◽  
Uniaxial Creep ◽  
Rupture Data

AbstractCommonly used small creep specimen types, such as ring and impression creep specimens, are capable of providing minimum creep strain rate data from small volumes of material. However, these test types are unable to provide the creep rupture data. In this paper the recently developed two-bar specimen type, which can be used to obtain minimum creep strain rate and creep rupture creep data from small volumes of material, is described. Conversion relationships are used to convert (i) the applied load to the equivalent uniaxial stress, and (ii) the load line deformation rate to the equivalent uniaxial creep strain rate. The effects of the specimen dimension ratios on the conversion factors are also discussed in this paper. This paper also shows comparisons between two-bar specimen creep test data and the corresponding uniaxial creep test data, for grade P91 steel at 650°C.

Analysis and Design of a Small, Two-Bar Creep Test Specimen

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Tom H. Hyde ◽  
Balhassn S. M. Ali ◽  
Wei Sun
Keyword(s):  
Finite Element ◽  
Creep Strain ◽  
Creep Test ◽  
Test Specimen ◽  
Test Method ◽  
Finite Element Analyses ◽  
Analysis And Design ◽  
Specimen Type ◽  
Reference Stress ◽  
Uniaxial Creep

In this paper, a new small-sized (two-bar) specimen type, which is suitable for use in obtaining both uniaxial creep strain and creep rupture life data, is described. The specimen has a simple geometry and can be conveniently machined and loaded (through pin-connections) for testing. Conversion relationships between the applied load and the corresponding uniaxial stress, and between the measured load-line deformations and the corresponding uniaxial minimum creep strain rate, have been obtained, based on the reference stress method (RSM), in conjunction with finite element analyses. Using finite element analyses the effects of the specimen dimensions on reference stress parameters have been investigated. On this basis, specimen dimension ratio ranges are recommended. The effects of friction, between the loading pins and the specimen surfaces, on the specimen failure time, are also investigated. Test results obtained from two-bar specimen tests and from corresponding uniaxial specimen tests, for a P91 steel at 600 °C, are used to validate the test method. These results demonstrated that the specimen type is capable of producing full uniaxial creep strain curves. The advantages of this new, small, creep test specimen, for determining uniaxial creep data, are discussed and recommendations for future research are given.

Creep Properties Assessment of Materials by a Small Cantilever Beam Specimen

2018 ◽  
Author(s):  
Fakun Zhuang ◽  
Shantung Tu ◽  
Guoshan Xie ◽  
Shanshan Shao ◽  
Luowei Cao
Keyword(s):  
Cantilever Beam ◽  
Creep Test ◽  
Uniaxial Stress ◽  
Test Method ◽  
Creep Model ◽  
Beam Specimen ◽  
Secondary Creep ◽  
Creep Tests ◽  
Creep Properties ◽  
Uniaxial Creep

Small specimen creep test techniques have been widely applied in the creep properties assessment of materials for the equipment in-service. In order to acquire the creep data accurately and conveniently, the creep test method with small cantilever beam specimens is proposed. On the basis of Norton-Bailey creep law, analytical creep model for the cantilever beam specimen is derived. With this model, the load can be converted to equivalent uniaxial stress and the displacement rate can be converted to equivalent uniaxial strain rate. The creep properties of Cr-Mo steel are assessed by the cantilever beam specimens creep tests. And the creep parameters are evaluated, which are compared to the uniaxial creep parameters. The results show that parameters obtained from the cantilever beam tests correspond reasonably well with those from uniaxial tests. It proves that the primary and secondary creep properties can be assessed by the cantilever beam specimen tests.

A Creep-Damage Constitutive Model for Sandstone

2012 ◽  
Vol 170-173 ◽  
pp. 289-294 ◽  
Author(s):  
Wei Wang ◽  
Jun Lv ◽  
Hai Cheng Wang
Keyword(s):  
Constitutive Model ◽  
Creep Test ◽  
Creep Damage ◽  
Creep Model ◽  
Whole Process ◽  
Proposed Model ◽  
Accelerated Creep ◽  
Damage Constitutive Model ◽  
Triaxial Creep ◽  
Triaxial Creep Test

Based on the results obtained by the triaxial creep test, a creep-damage constitutive model for sandstone is presented by using the damage theory and by introducing the concept of “the whole process of damage” into Burgers creep model. The parameters of the model are determined by fitting the creep test data. The result shows that the proposed model can not only describe efficiently the variation of decay and steady creep under relatively low stress condition, but also give a satisfied representation of damage behavior in accelerated creep stage.

Creep Life Prediction of HR3C Steel Using Creep Damage Models

2017 ◽  
Author(s):  
Hoomin Lee ◽  
Seok-Jun Kang ◽  
Jae-Boong Choi ◽  
Moon-Ki Kim
Keyword(s):  
Life Prediction ◽  
Power Plants ◽  
Creep Damage ◽  
Creep Rupture ◽  
Creep Life ◽  
Damage Models ◽  
Creep Life Prediction ◽  
Uniaxial Creep ◽  
Term Creep

The world’s energy market demands more efficient power plants, hence, the operating conditions become severe. For thermal plants, Ultra Super Critical (USC) conditions were employed with an operating temperature above 600°C. In such conditions, the main failure mechanism is creep rupture behavior. Thus, the accurate creep life prediction of high temperature components in operation has a great importance in structural integrity evaluation of USC power plants. Many creep damage models have been developed based on continuum damage mechanics and implemented through finite element analysis. The material constants in these damage models are derived from several accelerated uniaxial creep experiments in high stress conditions. In this study, the target material, HR3C, is an austenitic heat resistant steel which is used in reheater/superheater tubes of an USC power plant built in South Korea. Its creep life was predicted by extrapolating the creep rupture times derived from three different creep damage models. Several accelerated uniaxial creep tests have been conducted in various stress conditions in order to obtain the material constants. Kachanov-Rabotnov, Liu-Murakami and the Wen creep damage models were implemented. A comparative assessment on these three creep damage models were performed for predicting the creep life of HR3C steel. Each models require a single variable to fit the creep test curves. An optimization error function were suggested by the authors to quantify the best fit value. To predict the long term creep life of metallic materials, the Monkman-Grant model and creep rupture property diagrams were plotted and then extrapolated over an extended range. Finally, it is expected that one can assess the remaining lifetime of UCS power plants with such a valid estimation of long-term creep life.

Stress singularities at the free surface of an axisymmetric two-material creep test specimen

1997 ◽  
Vol 32 (2) ◽  
pp. 107-117 ◽  
Author(s):  
T H Hyde ◽  
W Sun
Keyword(s):  
Free Surface ◽  
Steady State ◽  
Creep Test ◽  
Test Specimen ◽  
Stress Singularity ◽  
Finite Element Analyses ◽  
Stress Singularities ◽  
Material Creep ◽  
Power Law Creep ◽  
Relative Creep

The nature of the stress singularity that occurs at the surface of an axisymmetric, two-material creep test specimen has been investigated. Steady state finite element analyses were obtained for this purpose, using Norton's power law creep equations having the same stress exponent for each material. The strength of the singularity was found to be strongly dependent upon the relative creep strengths of the two materials, but was surprisingly insensitive to the relative dimensions of the two materials. The implications of the results for practical situations are discussed.

Determination of Creep Damage Properties from a Miniature Three Point Bending Specimen Using an Inverse Approach

2017 ◽  
Vol 734 ◽  
pp. 260-272 ◽  
Author(s):  
J. Lu ◽  
A. Campbell-Brown ◽  
Shan Tung Tu ◽  
Wei Sun
Keyword(s):  
Power Plant ◽  
Creep Test ◽  
Test Specimen ◽  
Damage Model ◽  
Creep Damage ◽  
Material Strength ◽  
Element Analysis ◽  
Three Point Bending ◽  
Inverse Approach ◽  
Full Life

In this work, a novel method for determining the creep damage properties which can be used to represent the full life until failure from a miniature bending creep test specimen is developed based on a mathematical analysis and an inverse approach. Using the Kachanov-Rabotnov creep damage model, a mathematical expression for the deflection of a simply supported, rectangular miniature thin beam creep test specimen, under three-point bending (TPB), is derived. The outputs of these equations are iterated numerically using a MATLAB program. The time-dependent deflection curves are computed as the virtue TPB tests at various loads. The accuracy of the mathematical solutions is evaluated by the corresponding results obtained from finite element analysis. On this basis, an inverse method is then developed to obtain the creep and damage constants using a MATLAB optimisation scheme, where the primary creep is neglected. The results obtained for a power plant Grade 91 Cr steel is used for demonstration. The inverse approach developed has potential applications for assessing the high temperature material strength as part of a NDT procedure and for deriving the full life creep damage constitutive properties from a small volume of material, in particular, for various microstructure regions within a heat-affected zone of weldments, e.g. of power plant pipelines and aero-engine components.

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