48 Hour Multiaxial Creep and Creep Recovery of 2618 Aluminum Alloy at 200°C

1984 ◽  
Vol 51 (1) ◽  
pp. 125-132 ◽  
Author(s):  
J.-L. Ding ◽  
W. N. Findley
Keyword(s):  
Homogeneous Function ◽  
Maximum Shear Stress ◽  
Full Range ◽  
Viscoelastic Model ◽  
Multiple Integral ◽  
Constant Stress ◽  
Time Dependent ◽  
Creep Recovery ◽  
Aging Effects ◽  
Data Set

Data are reported from 48 hour constant multiaxial stress creep followed by 48 hour creep recovery with the magnitudes of the effective stress ranging from 34.5 MPa (5.00 ksi) to 175.5 MPa (25.46 ksi). They differed from a previous data set in the much longer constant-stress durations and the inclusion of data from low stress creep, compression creep, and short term aging tests. Data were represented by a viscous-viscoelastic model in which the time-dependent strain was resolved into recoverable and nonrecoverable components. Previous stress-strain relations for constant stress creep and recovery were modified to include the current experimental observations of the nonexistence of creep limits, negligible aging effects, and symmetry in tension and compression. The time dependence was represented by a power of time with different exponents for the recoverable and nonrecoverable components. A homogeneous function of maximum shear stress was developed to represent the full range of stress dependence of the nonrecoverable time-dependent components; the third-order multiple integral representation was used for the recoverable component.

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.

Creep of 2618 Aluminum Under Step Stress Changes Predicted by a Viscous-Viscoelastic Model

1980 ◽  
Vol 47 (1) ◽  
pp. 21-26 ◽  
Author(s):  
J. S. Lai ◽  
W. N. Findley
Keyword(s):  
Constitutive Equations ◽  
Superposition Principle ◽  
Viscoelastic Model ◽  
Multiple Integral ◽  
Constant Stress ◽  
Time Dependent ◽  
Stress Tests ◽  
Linear Elastic ◽  
Stress Changes ◽  
Dependent Strain

Nonlinear constitutive equations are developed and used to predict from constant stress data the creep behavior of 2618 Aluminum at 200°C (392°F) for tension or torsion stresses under varying stress history including stepup, stepdown, and reloading stress changes. The strain in the constitutive equation employed includes the following components: linear elastic, time-independent plastic, nonlinear time-dependent recoverable (viscoelastic), nonlinear time-dependent nonrecoverable (viscous) positive, and nonlinear time-dependent nonrecoverable (viscous) negative. The modified superposition principle, derived from the multiple integral representation, and strain-hardening theory were used to represent the recoverable and nonrecoverable components, respectively, of the time-dependent strain in the constitutive equations. Excellent-to-fair agreement was obtained between the experimentally measured data and the predictions based on data from constant-stress tests using the constitutive equations as modified.

Creep and Creep Recovery of 304 Stainless Steel at Low Stresses With Effects of Aging on Creep and Plastic Strains

1981 ◽  
Vol 48 (4) ◽  
pp. 785-790 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Plastic Strain ◽  
Viscoelastic Model ◽  
Time Dependent ◽  
304 Stainless Steel ◽  
Dislocation Creep ◽  
Creep Recovery ◽  
Power Functions ◽  
Transition Stress ◽  
Stress Levels

Creep and creep recovery data of 304 stainless steel are reported for experiments at low stress levels under 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. Only part of the creep strain at low stresses was recovered upon complete unloading following creep (as also found at high stresses), and each time-dependent strain data was well represented by a power function of time. But the stress dependence below a transition stress was approximately a linear relation with no creep limits and no cross effects such as were found in a previous analysis for higher stress levels above a transition stress. The transition stress for nonrecoverable strains agrees with the Frost-Ashby boundary between diffusional flow and dislocation creep. Aging decreased the creep rate and plastic strain. Results for different times of aging at 593°C (1100°F) under pure tension stresses were well represented by power functions of aging time up to 1000 h for each creep component and plastic strain.

Time-Dependent Uniaxial Ratchetting of Ultrahigh Molecular Weight Polyethylene Polymer: Viscoelastic–Viscoplastic Constitutive Model

2016 ◽  
Vol 83 (10) ◽  
Author(s):  
Kaijuan Chen ◽  
Guozheng Kang ◽  
Chao Yu ◽  
Fucong Lu ◽  
Han Jiang
Keyword(s):  
Molecular Weight ◽  
Constitutive Model ◽  
Viscoelastic Model ◽  
Hysteresis Loops ◽  
Ultrahigh Molecular Weight Polyethylene ◽  
Time Dependent ◽  
Creep Recovery ◽  
Tension Tests ◽  
Proposed Model ◽  
Ultrahigh Molecular Weight

Uniaxial tension–unloading recovery, creep-recovery, and stress-controlled cyclic tests are first performed to investigate the recoverable viscoelasticity and irrecoverable viscoplasticity (including the uniaxial ratchetting) of ultrahigh molecular weight polyethylene (UHMWPE) polymer at room temperature. The results show that obvious time-dependent ratchetting occurs in the asymmetrical stress-controlled cyclic tension–compression and tension–tension tests of the UHMWPE, and total ratchetting strain consists of both recoverable viscoelastic and irrecoverable viscoplastic parts. Based on the experimental observation, a new viscoelastic–viscoplastic constitutive model is proposed to describe the time-dependent ratchetting of the UHMWPE. In the proposed model, the viscoplastic strain is set to be contributed simultaneously by the unified viscoplastic and creep ones. Meanwhile, a memory surface is introduced into the viscoelastic model to improve the description to the shapes of stress–strain hysteresis loops. Finally, the proposed model is verified by comparing the predictions with the corresponding experimental results of the UHMWPE. It is clearly demonstrated that the proposed model predicts the creep, viscoelastic recovery, and uniaxial time-dependent ratchetting of the UHMWPE well.

Creep and Recovery of 2618 Aluminum Alloy Under Combined Stress With a Representation by a Viscous-Viscoelastic Model

1978 ◽  
Vol 45 (3) ◽  
pp. 507-514 ◽  
Author(s):  
W. N. Findley ◽  
J. S. Lai
Keyword(s):  
Mathematical Model ◽  
Time Dependence ◽  
Viscoelastic Model ◽  
Multiple Integral ◽  
Time Dependent ◽  
Strain Component ◽  
Combined Stress ◽  
Recoverable Strain ◽  
Creep And Recovery ◽  
Mathematical Expressions

Creep and recovery data are presented for combined tension and torsion of 2618 Aluminum at 200°C (392°F). These data are represented by a mechanical-mathematical model in which the strain is resolved into five components: elastic, time-independent plastic, recoverable viscoelastic, time-dependent nonrecoverable viscous (positive) and time-dependent nonrecoverable viscous (negative). By using recovery data the recoverable component is separated from the nonrecoverable creep strain. Results show that the time-dependence may be represented by a power of time (independent of stress) and that the time-dependence of the recoverable and nonrecoverable strains are the same. It is also shown that the proportion of recoverable versus nonrecoverable strain may be taken to be independent of stress. The mathematical expressions developed describe quite well the creep and recovery under tension and/or torsion. Results are presented in a form which may prove suitable for predicting creep or relaxation under variable input using the modified superposition simplification of the multiple integral representation for the recoverable strain component and strain hardening for the nonrecoverable component. Comparison between predicted strain or stress and actual tests under different variable stress or strain histories will be presented in subsequent papers.

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.

Application of a Viscoelastic Model for Polyester Mooring

2010 ◽  
Author(s):  
J. W. Kim ◽  
J. H. Kyoung ◽  
A. Sablok
Keyword(s):  
Material Properties ◽  
Viscoelastic Model ◽  
Practical Method ◽  
Time Dependent ◽  
Mooring Line ◽  
New Model ◽  
Global Performance ◽  
Excitation Period ◽  
Linear Viscoelastic ◽  
Floating Platforms

A new practical method to simulate time-dependent material properties of polyester mooring line is proposed. The time-dependent material properties of polyester rope are modeled with a standard linear solid (SLS) model, which is one of the simplest forms of a linear viscoelastic model. The viscoelastic model simulates most of the mechanical properties of polyester rope such as creep, strain-stress hysteresis and excitation period-dependent stiffness. The strain rate-stress relation of the SLS model has been re-formulated to a stretch-tension relation, which is more suitable for implementation into global performance and mooring analyses tools for floating platforms. The new model has been implemented to a time-domain global performance analysis software and applied to simulate motion of a spar platform with chain-polyester-chain mooring system. The new model provides accurate platform offset without any approximation on the mean environmental load and can simulate the transient effect due to the loss of a mooring line during storm conditions, which has not been possible to simulate using existing dual-stiffness models.

Moment-tensor solutions for the 24 November 1987 Superstition Hills, California, earthquakes

1989 ◽  
Vol 79 (2) ◽  
pp. 493-499
Author(s):  
Stuart A. Sipkin
Keyword(s):  
Main Shock ◽  
Moment Tensor ◽  
Time Dependent ◽  
Origin Time ◽  
Data Set ◽  
Filter Theory ◽  
Long Period ◽  
Seismograph Network ◽  
Scalar Moment

Abstract The teleseismic long-period waveforms recorded by the Global Digital Seismograph Network from the two largest Superstition Hills earthquakes are inverted using an algorithm based on optimal filter theory. These solutions differ slightly from those published in the Preliminary Determination of Epicenters Monthly Listing because a somewhat different, improved data set was used in the inversions and a time-dependent moment-tensor algorithm was used to investigate the complexity of the main shock. The foreshock (origin time 01:54:14.5, mb 5.7, Ms 6.2) had a scalar moment of 2.3 × 1025 dyne-cm, a depth of 8 km, and a mechanism of strike 217°, dip 79°, rake 4°. The main shock (origin time 13:15:56.4, mb 6.0, Ms 6.6) was a complex event, consisting of at least two subevents, with a combined scalar moment of 1.0 × 1026 dyne-cm, a depth of 10 km, and a mechanism of strike 303°, dip 89°, rake −180°.

scholarly journals Analysis of genome-wide mutation profile and establishment of risk signature for prognosis of bladder cancer

2020 ◽  
Author(s):  
Yanyun Zhao ◽  
Rong Ma ◽  
Fangxiao Liu ◽  
Liwen Zhang ◽  
Xuemei Lv ◽  
...  
Keyword(s):  
Bladder Cancer ◽  
Cox Regression ◽  
Predictive Accuracy ◽  
Predictive Ability ◽  
Time Dependent ◽  
Net Benefit ◽  
Data Set ◽  
Clinical Prognosis ◽  
Cox Regression Analysis ◽  
Mutation Profile

Abstract Background: Emerging studies have shown that a variety of gene mutations occur in development and progression of cancer and highly mutation genes could play oncogenic or tumor suppressive roles in cancer. Therefore, our aim is to explore mutation genes which affect the prognosis of bladder.Methods: Mutation profile was obtained and analyzed from TCGA data set. A mutation-based signature was established by multivariable Cox regression analysis. Kaplan-Meier was performed to assess the prognostic power of signature. Time-dependent ROC was conducted to evaluate predictive accuracy of signature for bladder cancer patients.Results: There are 20177 genes have alteration in 403 bladder patients and 662 of them were frequently variation (mutation frequency > 5%). In this study, we assessed the prognostic predictive ability of 662 highly mutated genes and identified a mutation signature as an independent indicator for predicting the prognosis of bladder. The time-dependent ROC showed that AUC were 0.893, 0.896, 0.916 and 0.965 at 1, 3, 5 and 10 year, respectively. Stratified analysis and Multivariate Cox analysis showed that this mutation signature was reliable and independent biomarker. Furthermore, the nomogram predictive model can be used to effectively predict clinical prognosis of bladder patients. The decision analysis curve showed patients with risk threshold of 0.03-0.92 potentially yielded clinical net benefit. Finally, we identified several signaling pathways that associated with risk score by GSEA and KEGG analysis including PI3K-Akt signaling pathway and so on.Conclusions: In general, this study provide an optimal mutation signature as potential prognosis biomarker for bladder patients.

scholarly journals The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems

2018 ◽  
Author(s):  
Kamolphat Atsawawaranunt ◽  
Laia Comas-Bru ◽  
Sahar Amirnezhad Mozhdehi ◽  
Michael Deininger ◽  
Sandy P. Harrison ◽  
...  
Keyword(s):  
Working Group ◽  
Climate Models ◽  
Full Range ◽  
Global Changes ◽  
Sufficient Information ◽  
Data Set ◽  
Oxygen And Carbon Isotope ◽  
Cave System ◽  
Out Of Sample ◽  
Age Model

Abstract. Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. These records are increasingly being used to provide “out-of-sample” evaluations of isotope-enabled climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The SISAL database contains data for individual speleothems, grouped by cave system. Stable isotopes of oxygen and carbon (δ18O, δ13C) measurements are referenced by distance from the top or youngest part of the speleothem. Additional tables provide information on dating, including information on the dates used to construct the original age model and sufficient information to assess the quality of each data set and to erect a standardized chronology across different speleothems. The metadata table provides location information, information about the full range of measurements carried out on each speleothem and information about the cave system that is relevant to the interpretation of the records, as well as citations for both publications and archived data. The compiled data are available at http://dx.doi.org/10.17864/1947.139.

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