Correlation of Tension Creep Tests With Relaxation Tests

1949 ◽  
Vol 16 (2) ◽  
pp. 208
Author(s):  
Irving Roberts
Keyword(s):  
Analytical Solutions ◽  
Creep Data ◽  
Creep Tests ◽  
Relaxation Problem ◽  
Direct Substitution

Abstract This paper shows that analytical solutions to the bolt relaxation problem, based upon empirical creep-data equations may be obtained by direct substitution, rather than by differentiation and integration, as was done by Soderberg, Popov, and Housner.

Applications of Creep Tests

1933 ◽  
Vol 1 (3) ◽  
pp. 87-97
Author(s):  
Gleason H. MacCullough
Keyword(s):  
Stress Distribution ◽  
Internal Pressure ◽  
Analytical Solutions ◽  
Practical Interest ◽  
Creep Data ◽  
Pure Bending ◽  
Creep Tests ◽  
Circular Shaft ◽  
Pipe Joint

Abstract Analytical solutions of problems which involve creep phenomena and which are of practical interest are at present very limited in number. This paper discusses four specific problems for which solutions have been presented: namely, the problem of the flanged and bolted pipe joint under creep conditions, and the three problems of stress distribution and creep in thick-walled cylinders under internal pressure, in a beam subjected to pure bending, and in a solid circular shaft under torsion. These solutions will illustrate the kind of creep data which the designer desires the experimenter to furnish.

Microstructures of Grade 91 Steels Under Long-Term Creep Conditions

2018 ◽  
Author(s):  
Kenji Kako ◽  
Susumu Yamada ◽  
Masatsugu Yaguchi ◽  
Yusuke Minami
Keyword(s):  
Remaining Life ◽  
Martensitic Steels ◽  
Creep Data ◽  
Creep Life ◽  
Creep Tests ◽  
Microstructural Observation ◽  
Type Iv ◽  
Grade 91 ◽  
Term Creep

Type IV damage has been found at several ultra-supercritical (USC) plants that used high-chromium martensitic steels in Japan, and the assessment of the remaining life of the steels is important for electric power companies. The assessment of the remaining life needs long-term creep data for over 10 years, but such data are limited. We have attempted to assess the remaining life by creep tests and by microstructural observation of Grade 91 steels welded pipes which were used in USC plants for over 10 years. Following the results of microstructural observation of USC plant pipes, we find that microstructures, especially distribution of MX precipitates, have large effect on the creep life of Grade 91 steels.

Concerning a Creep Surface Derived From a Multiple Integral Representation for 304 Stainless Steel Under Combined Tension and Torsion

1978 ◽  
Vol 45 (4) ◽  
pp. 773-779 ◽  
Author(s):  
R. Mark ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Creep Rate ◽  
Integral Representation ◽  
Power Function ◽  
Multiple Integral ◽  
304 Stainless Steel ◽  
Creep Data ◽  
Creep Tests ◽  
Third Order ◽  
Good Agreement

It is shown that a creep surface, defined in terms of a prescribed creep rate, can be determined from the multiple integral formulation representing the creep data. The creep surface for 304 stainless steel was found to be in good agreement with a Mises ellipse. Observed creep rate vectors for this alloy were found to be normal to a Mises ellipse. These results were obtained from creep tests performed on 304 stainless steel under combined tension and torsion at 593°C (1100°F). Creep strains observed for at least 100 hr were adequately represented by a power function of time, the exponent of which was independent of stress. A third-order multiple integral representation together with a limiting stress below which creep does not occur was employed to describe satisfactorily the constant stress creep data.

Long Term Creep Life Prediction of New and Service Exposed P91 Steel

2018 ◽  
Author(s):  
Muneeb Ejaz ◽  
Norhaida Ab Razak ◽  
Andrew Morris ◽  
Scott Lockyer ◽  
Catrin M. Davies
Keyword(s):  
Tensile Strength ◽  
Creep Behaviour ◽  
Equivalent Stress ◽  
Practical Reasons ◽  
Creep Data ◽  
Short Term ◽  
Creep Tests ◽  
High Temperature Components ◽  
Term Creep

P91 steels are widely used in high temperature components for power generation. Creep data is often generated through accelerated short term creep tests, for practical reasons, via increasing stress or temperature though this may alter the creep behaviour. Through normalising the creep test stress by tensile strength the Wilshire models reduce the batch to batch scatter in the creep data and enable the prediction of long term creep data from relatively short term test results. In this work it is shown that the Wilshire models fitted to uniaxial creep rupture data can be used to predict failure in both as cast and service exposed multiaxial tests. This is provided that the equivalent stress is the rupture controlling stress, as is the case for the P91 tests examined, and the tensile strength is measured as part of the test programme.

Creep Fatigue Interactions in a 1 CrMo V Steel

1976 ◽  
Vol 190 (1) ◽  
pp. 319-330 ◽  
Author(s):  
E.G. Ellison ◽  
A.J.F. Paterson
Keyword(s):  
Plastic Strain ◽  
High Strain ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Cyclic Creep ◽  
Creep Data ◽  
Creep Tests ◽  
Brittle Transition ◽  
Creep Fatigue ◽  
Cyclic Plastic Strain

Static and cyclic creep tests have been carried out on a 1 Cr Mo V steel at 565 °C. In addition, the effects of prior high strain fatigue on subsequent creep behaviour has been studied. A well defined ductile/brittle transition was noted which was unaffected by the type of load controlled cycle. The material softened under cyclic plastic strain and no experimental evidence was obtained which indicated that fatigue and creep damage interacted in a load controlled test to give rise to unexpectedly short lives. The conclusion derived is that “softened creep” data should be used in predictions of deformation and rupture behaviour, and that the use of virgin creep data can give rise to substantial errors.

Creep Model Based on Theta Projection and Omega Method for Predicting the Creep Behavior of Alloy

2007 ◽  
Vol 353-358 ◽  
pp. 533-536
Author(s):  
Bong Min Song ◽  
Jong Yup Kim ◽  
Joon Hyun Lee
Keyword(s):  
Creep Behavior ◽  
Constant Load ◽  
Control Mode ◽  
Creep Model ◽  
Test Results ◽  
Creep Data ◽  
Creep Tests ◽  
Omega Method ◽  
Improved Model ◽  
Term Creep

Creep testing of Alloy 718 has been carried out at various loads in the temperature range near 650°C in constant load control mode in order to understand how to predict the creep behavior including tertiary creep. The test results have been used for evaluating the existed models, such as Theta projection and Omega method that have been widely used for predicting long term creep strain and rupture time. After determining variables and material parameters of each method with the test results, estimated creep data from each model have been compared with the each measured creep data from the creep tests. The root cause of the discrepancy between estimated and measured data has been analyzed in order to improve the existed methods. The reliability of the improved model has been evaluated in relation to creep data.

Prediction of Creep Life on Notched Bar Specimens of Grade 92 Steel

2016 ◽  
Author(s):  
Haruhisa Shigeyama ◽  
Yukio Takahashi ◽  
Jonathan Parker
Keyword(s):  
Finite Element ◽  
Creep Damage ◽  
Creep Data ◽  
Creep Failure ◽  
Creep Tests ◽  
Energy Fraction ◽  
Damage Models ◽  
Finite Element Software ◽  
Notched Specimens ◽  
Life Fraction

Creep tests on two kinds of circumferentially notched round bar specimens as well as plain bar specimen were performed to obtain the multiaxial and uniaxial creep data. Creep damage models of strain fraction and energy fraction rule were developed using these creep data. Then creep damage analyses using a finite element software, MSC Marc, were carried out on notched specimens of both types and creep failure lives were predicted using the creep damage models of classical life fraction rule and developed strain or energy fraction rule. Experimental failure lives of all the conditions of notched specimens were compared with analytical results. As a result, creep failure lives obtained by life fraction rule were underestimated in the short term region and overestimated in the long term region. On the other hands, it is apparent that the majority of creep failure lives obtained by strain and energy fraction rule were predicted with an accuracy within a factor of two. Furthermore, some interrupted creep tests and creep void observations were conducted on the notched specimens of both types. The distributions of creep void number density were in good agreement with the distributions of creep damage calculated by finite element analyses.

Creep and strength testing of frozen saline fine-grained soils

1984 ◽  
Vol 21 (3) ◽  
pp. 518-529 ◽  
Author(s):  
J. F. Nixon ◽  
G. Lem
Keyword(s):  
Shear Strength ◽  
Creep Rate ◽  
Constant Strain Rate ◽  
Frozen Soil ◽  
Unfrozen Water ◽  
Saline Soils ◽  
Creep Data ◽  
Creep Tests ◽  
Test Environment ◽  
Fine Grained

Little creep data is available for frozen, fine-grained saline soils. Salinity accelerates the creep rate of a frozen soil under load and reduces its shear strength owing to the higher unfrozen water contents in the pore phase. Creep data for saline fine-grained soils are required by engineers and scientists working in areas of coastal or offshore permafrost. The data are also used in projects involving artificial freezing of saline soils.This paper describes the results of 34 creep tests and 11 time-dependent strength tests carried out on saline soils. The tests were carried out for two different research programs; consequently, two different fine-grained soil types were used. Most of the tests were carried out in a constant stress and constant temperature creep test environment. Some were completed in a triaxial (constant strain rate) test format, in order to extend the data base to an area of higher strain rates. The range of temperatures was −2.3 to −25 °C, the range of stresses in the creep tests was 30–400 kPa, and the salinity was varied from 0–35 parts per thousand (ppt). Particular attention was paid to the lower stresses (30–200 kPa) and intermediate to high salinities (18–35 ppt). A high percentage of the creep tests was completed in the temperature range −5 to −10 °C, as this appears to be a typical ground temperature in coastal permafrost areas in Arctic Canada.Results indicate that the presence of pore fluid with a salinity approaching that of seawater causes a 10- to 100-fold increase in uniaxial creep rate, which can result in significant decreases in shear strength and foundation bearing capacity in saline permafrost areas.Soil resistivity tests were also carried out on frozen samples of different salinities. A strong correlation between resistivity and pore water salinity emerged. This has application in the interpretation of results from electrical resistivity surveys in permafrost. Key words: permafrost, saline, creep, strength, resistivity, fine-grained, offshore permafrost.

Creep Behavior of an Al2O3-Sic Composite

1988 ◽  
Vol 120 ◽  
Author(s):  
P. Lipetzky ◽  
S. R. Nutt ◽  
P. F. Becher
Keyword(s):  
Deformation Mechanisms ◽  
Alumina Powder ◽  
Creep Data ◽  
Volume Percent ◽  
Temperature Dependent ◽  
Creep Tests ◽  
Sic Whiskers ◽  
Alumina Composite ◽  
Shock Resistance ◽  
Stress Dependent

AbstractThe addition of SiC whiskers to Al2O3 causes significant improvement in mechanical properties, including fracture toughness, thermal shock resistance, and creep resistance. The creep response of a whisker-reinforced alumina composite has been measured using four-point flexural loading at temperatures of 1200 and 1300C. Composites were fabricated by hot-pressing a blend of alumina powder with 33 volume percent SiC whiskers. The creep data showed a stress-dependent stress exponent equal to 1 at low stress levels and ranging from 4–6 at higher stresses. The applied stress at which the transition occurred was temperature dependent and ranged from 50–125 MPa. Mechanisms of creep deformation were determined from TEM observations of specimens prepared from interrupted creep tests. Voids were observed at grain boundary-interface junctions in tensile regions and whiskers within the composite were sometimes oxidized where voids had formed. TEM observations from specific stages of steady state creep reached under different applied loads are presented, and the relative contributions of different deformation mechanisms are discussed.

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