Creep and Plastic Strains Under Side Steps of Tension and Torsion for 304 Stainless Steel at 593°C

1983 ◽  
Vol 50 (3) ◽  
pp. 580-586 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Viscoelastic Model ◽  
Single Step ◽  
304 Stainless Steel ◽  
Plastic Strains ◽  
Test Results ◽  
Aging Effects ◽  
Creep And Recovery ◽  
Stress Changes ◽  
Abrupt Changes ◽  
Step Down

Results of nonproportional stress changes on creep and plastic strains resulting from abrupt changes in proportion of tension and torsion are reported. Both step-up and step-down changes are included. Constitutive equations based on data for single step creep and recovery tests previously reported are used to describe the test results. A viscous-viscoelastic model with aging effects and modifications for step-down tests predicted the creep behavior reasonably well. The prediction of time-independent plastic strains is also described.

Creep and Plastic Strains Under Stress Reversal in Torsion With and Without Simultaneous Tension for 304 Stainless Steel at 593°C

1983 ◽  
Vol 50 (3) ◽  
pp. 587-592 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Viscoelastic Model ◽  
Single Step ◽  
304 Stainless Steel ◽  
Creep Recovery ◽  
Plastic Strains ◽  
Test Results ◽  
Aging Effects ◽  
Stress Changes ◽  
Constant Tension ◽  
Stress Reversals

Results of creep experiments under stress reversals in torsion with and without constant tension are reported. Constitutive equations based on data for single step creep and creep recovery tests previously reported are used to describe the test results. A viscous-viscoelastic model with aging effects and modifications for step-down stress changes and stress reversals predicted the creep behavior reasonably well. The prediction of time-independent plastic strains is also described.

Creep and Plastic Strains of 304 Stainless Steel at 593°C Under Step Stress Changes, Considering Aging

1982 ◽  
Vol 49 (2) ◽  
pp. 297-304 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Constitutive Equations ◽  
Time Dependent ◽  
304 Stainless Steel ◽  
Flow Rule ◽  
Strain Component ◽  
Plastic Strains ◽  
Aging Effects ◽  
Stress Changes ◽  
Step Down

Nonlinear constitutive equations for varying stress histories are developed and used to predict the creep behavior of 304 stainless steel at 593°C (1100°F) under variable tension or torsion stresses including reloading, complete unloading, step-up, and step-down stress changes. The strain in the constitutive equations (a viscous-viscoelastic model) consists of: linear elastic, time-independent plastic, time-dependent-recoverable viscoelastic, and time-dependent-nonrecoverable viscous components. For variable stressing, the modified superposition principle, derived from the multiple integral representation, and the strain hardening theory were used to represent the recoverable and nonrecoverable components, respectively, of the time-dependent strain. Time-independent plastic strains were described by a flow rule of similar form to that for nonrecoverable, time-dependent strains. The material constants of the theory were determined from constant stress creep and creep recovery data. Considerable aging effects were found and the effects on the strain components were incorporated in each strain predicted by the theory. Some modifications of the theory for the viscoelastic strain component under step-down stress changes were made to improve the predictions. The final predictions combining the foregoing features made satisfactory agreements with the experimental creep data under step stress changes.

On the Nonlinear Viscoelastic Behaviour of the PVC-Coated Fabric

2010 ◽  
Vol 160-162 ◽  
pp. 1476-1481 ◽  
Author(s):  
Wu Lian Zhang ◽  
Xin Ding ◽  
Xu Dong Yang
Keyword(s):  
Viscoelastic Model ◽  
Constitutive Relationship ◽  
Viscoelastic Behaviour ◽  
Viscoelastic Response ◽  
Nonlinear Parameters ◽  
Creep And Recovery ◽  
Nonlinear Viscoelastic ◽  
Coated Fabric ◽  
Nonlinear Viscoelastic Model

The nonlinear viscoelastic response of a PVC-Coated Fabric has been studied. For the needs of the present study, creep and recovery tests in tension of both the warp and the weft directions at the different stress levels were executed while measurements were made of the creep and recovery strain response of the system. For the description of the viscoelastic behaviour of the material, Schapery’s nonlinear viscoelastic model was used. For the description of the nonlinear viscoelastic response and the determination of the nonlinear parameters, a method by using a combination of analytical formulations and numerical procedures based on a modified version of Schapery’s constitutive relationship where an instantaneous plastic and a transient plastic terms were added, has been developed. The method has been successfully applied to the current tests.

scholarly journals Effects of extended short-term aging duration on asphalt binder behaviour at high temperatures

2016 ◽  
Vol 11 (4) ◽  
pp. 302-312 ◽  
Author(s):  
Meor Othman Hamzah ◽  
Seyed Reza Omranian
Keyword(s):  
Response Surface ◽  
Response Surface Method ◽  
High Temperatures ◽  
Test Temperature ◽  
Asphalt Binder ◽  
Pavement Performance ◽  
Test Results ◽  
Aging Effects ◽  
Short Term ◽  
Surface Method

Many factors affecting pavement performance include variations in binder composition and environmental conditions during asphalt mixture production. Hence, predicting pavement performance is a difficult task. This paper aims to investigate the effects of short term aging on binder viscosity at high temperature. In order to predict the effects of short term aging on the asphalt binder viscosity at high temperatures, a Response Surface Method was performed on the Rotational Viscometer test results. An experimental matrix was planned based on the central composite design for aging duration and test temperature. The test results showed that aging increased the binder viscosity, while increasing test temperature decreased the corresponding value. However, aging effects differ and depend on binder types, test temperatures and aging conditions. It was also found that the Response Surface Method is a fast, effective and reliable method to predict the effects of aging on binder viscosity behaviour at high temperatures.

scholarly journals Multiple Comparison with a Control Using Step-down Procedure

2020 ◽  
Vol 8 (2) ◽  
Author(s):  
Bumrungsak Phuenaree ◽  
Suttinee Kaewtaworn
Keyword(s):  
Error Rate ◽  
Single Step ◽  
Multiple Comparison ◽  
Control Group ◽  
Test Statistics ◽  
Familywise Error Rate ◽  
Dunnett Test ◽  
The Family ◽  
Bonferroni Test ◽  
Step Down

The purpose of this research was to compare the efficiency of single-step procedures and the step-down procedures in order to test for multiple comparison with a control group. Four tests; Dunnett test, Step-down Dunnett test, Bonferroni test and Bonferroni-Holm test, was considered. The performance of these tests was evaluated in terms of the family wise error rate, any-pair power and all-pairs power. A Monte Carlo simulation was performed with repeated 10,000 times. The results showed that the familywise error rate of all test statistics closed to the nominal level. The empirical power of step-down procedures were higher than the single-step procedures, and the step-down Dunnett test gave the highest power.

Creep and Creep Recovery of 304 Stainless Steel Under Combined Stress With a Representation by a Viscous-Viscoelastic Model

1980 ◽  
Vol 47 (4) ◽  
pp. 755-761 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Viscoelastic Model ◽  
Multiple Integral ◽  
Time Dependent ◽  
304 Stainless Steel ◽  
Creep Recovery ◽  
Strain Component ◽  
Stress Dependence ◽  
Nonlinear Stress ◽  
Stress States

Creep and creep-recovery data of 304 stainless steel are reported for experiments under constant combined tension and torsion at 593°C (1100°F). The data were represented by a viscous-viscoelastic model in which the strain was resolved into five components—elastic, plastic (time-independent), viscoelastic (time-dependent recoverable), and viscous (time-dependent nonrecoverable) which has separate positive and negative components. The data are well represented by a power function of time for each time-dependent strain. By applying superposition to the creep-recovery data, the recoverable creep strain was separated from the nonrecoverable. The form of stress-dependence associated with a third-order multiple integral representation was employed for each strain component. The time-dependent recoverable and nonrecoverable strains had different nonlinear stress dependence; but, the time-independent plastic strain and time-dependent nonrecoverable strain had similar stress-dependence. A limiting stress below which creep was very small or negligible was found for both recoverable and nonrecoverable components as well as a yield limit. The limit for recoverable creep was substantially less than the limits for nonrecoverable creep and yielding. The results showed that the model and equations used in the analysis described quite well the creep and creep-recovery under the stress states tested.

scholarly journals Development of novel apparatus to obtain soil resistance–displacement relationship for well conductor fatigue analysis

2017 ◽  
Vol 54 (10) ◽  
pp. 1435-1446 ◽  
Author(s):  
Arash Zakeri ◽  
Hendrik Sturm ◽  
Rune Dyvik ◽  
Philippe Jeanjean
Keyword(s):  
Cyclic Loading ◽  
Interaction Mechanism ◽  
Physical Modelling ◽  
Fatigue Analysis ◽  
Test Results ◽  
Major Step ◽  
Soil Response ◽  
Geotechnical Centrifuge ◽  
Field Samples ◽  
Stress Changes

An important aspect of deepwater well integrity is development of accurate conductor fatigue analysis due to cyclic loading during drilling operations. Fatigue damage in a structure occurs from stress changes in response to cyclic loading. In practice, the lateral cyclic soil response is typically modelled using Winkler lateral load–displacement (p–y) springs. However, recently developed soil models for conductor fatigue analysis are based on physical modelling in a geotechnical centrifuge. Notwithstanding the advantages of centrifuge modelling for investigating the conductor–soil interaction mechanism, development of simple laboratory tools to obtain p–y data directly from intact soil samples obtained from the field can also be very beneficial. This paper describes the development of a novel apparatus to obtain p–y and soil damping relationships from field samples specifically tailored for well conductor fatigue analysis. In addition, it compares test results obtained using reconstituted kaolin clay and intact natural Onsøy clay with centrifuge test results; ultimately demonstrating a satisfactory agreement between the two techniques. The results are highly encouraging and are believed to present a major step forward in deepwater well conductor fatigue analysis. The findings may also be beneficial to the offshore renewable energy sector.

Failure Mode of Pipes Containing Circumferential Cracks Under Bending and Its Consequence on the Application of NSCM Criterion

2003 ◽  
Author(s):  
P. P. Milella ◽  
N. Bonora ◽  
D. Gentile
Keyword(s):  
Plastic Zone ◽  
Room Temperature ◽  
Plastic Hinge ◽  
304 Stainless Steel ◽  
Test Results ◽  
Screening Criteria ◽  
Four Point Bending ◽  
Zone Parameter ◽  
Line Theory ◽  
Straight Ahead

The results of some 60 tests performed in Italy on 2”, 4”, 6” and 8” pipes of A 106 B and 304 stainless steel, carrying circumferential through-wall cracks of various size under four point bending conditions (FPB), at room temperature and 300° C, have been analyzed using the Net Section Collapse Moment Criterion (NSCM) and the dimensionless plastic zone parameter (DPZP). Most of the test results have shown that the NSCM applies even though the DPZP is lower than unity. This apparent inconsistency is due to the fact that cracked pipes under bending fail by plastic hinge formation of the type occurring in FPB specimens carrying notches, like the Charpy VN ones, as predicted by the slip line theory. Under these conditions, two half circle plastic zones develop at both sides of the notch while the plastic zone straight ahead the notch tip is almost negligible. FE Calculations have confirmed this behavior: the plastic zone underneath the crack tip has not yet reached the neutral axis when the plastic hinge is formed on the sides of the piping, making the NSCM applicable. This, actually, implies that the DPZP as presently used in the screening criteria is not precisely the proper parameter to adopt in the assessment of the NSCM criterion applicability.

scholarly journals Virtual Point Control for Step-Down Perturbations and Downhill Slopes in Bipedal Running

2020 ◽  
Vol 8 ◽  
Author(s):  
Özge Drama ◽  
Alexander Badri-Spröwitz
Keyword(s):  
Control Method ◽  
Single Step ◽  
Bipedal Robots ◽  
Natural Motion ◽  
Reaction Forces ◽  
Point Control ◽  
Step Down ◽  
Virtual Point ◽  
And Control ◽  
Level Running

Bipedal running is a difficult task to realize in robots, since the trunk is underactuated and control is limited by intermittent ground contacts. Stabilizing the trunk becomes even more challenging if the terrain is uneven and causes perturbations. One bio-inspired method to achieve postural stability is the virtual point (VP) control, which is able to generate natural motion. However, so far it has only been studied for level running. In this work, we investigate whether the VP control method can accommodate single step-down perturbations and downhill terrains. We provide guidelines on the model and controller parameterizations for handling varying terrain conditions. Next, we show that the VP method is able to stabilize single step-down perturbations up to 40 cm, and downhill grades up to 20–40° corresponding to running speeds of 2–5 ms−1. Our results show that the VP approach leads to asymmetrically bounded ground reaction forces for downhill running, unlike the commonly-used symmetric friction cone constraints. Overall, VP control is a promising candidate for terrain-adaptive running control of bipedal robots.

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