Creep, Recovery, and Permanent Set for GR-S and Hevea

1949 ◽  
Vol 22 (1) ◽  
pp. 105-117 ◽  
Author(s):  
S. D. Gehman
Keyword(s):  
Creep Test ◽  
Creep Recovery ◽  
Crystalline Phases ◽  
Elastic Network ◽  
Permanent Set ◽  
Large Ratio ◽  
Secondary Bond ◽  
Creep Curves ◽  
Eyring Theory ◽  
Strain Axis

Abstract A study was made of creep, recovery, and permanent set of Hevea and GR-S over a 1000-hour period and a range of elongations at 35° C. Creep of GR-S is greater than that of Hevea. The stress of GR-S is considered to be supported to a greater extent by a relatively unstable secondary bond structure. This is consistent with the large creep values of GR-S at low elongations and the large ratio of primary or recoverable creep to permanent set. Hevea, in contrast, shows low creep at both high and low elongations and maximum creep at intermediate elongations for which the structure is heterogeneous, consisting of amorphous and crystalline phases. A procedure was worked out for determining the contribution of permanent set to the observed creep. The creep curves were concave to the strain axis when plotted against logarithmic time. After correction was made for permanent set, they were found to be approximately linear, thus extending the range of application of the Tobolsky-Eyring theory of creep. At the start of the creep test the flow appears to be due largely to the reversible yielding of relatively weak bonds which can reform under the action of the elastic network when the stress is removed. For longer periods of time, or for higher elongations, the flow involves more deep seated changes in structure. Larger units of structure are displaced or stronger bonds broken with resultant permanent molecular displacements upon removal of the stress. For Hevea at high elongations all of the flow was accounted for by permanent set.

Application of Hypotheses Theory during Creep Curves Assesment

2017 ◽  
Vol 1142 ◽  
pp. 367-370
Author(s):  
Martin Reznicek ◽  
Lenka Hylova ◽  
Michal Stanek ◽  
Martin Ovsik
Keyword(s):  
Creep Test ◽  
Confidence Level ◽  
Subjective Assessment ◽  
Measured Data ◽  
Whitney Test ◽  
Current State ◽  
Mann Whitney Test ◽  
Creep Curves

This article is focused on a test assesment with a low repeatability, which is typical of its financial and time severity. In the introduction of this work the assessment of the current state of the solved problem concentrated on the creep test assesment is carried out, which is typical of its low repeatability. These results are subsequently graphically confronted with the subjective assessment of the observer and using Mann-Whitney test. This test is there used for finding if measured data come from the same basic file or come from the selected confidence level. The results show the significance of using this test, which is calculated with certain probability.

The Creep Recovery of a 0.17 per cent Carbon Steel

1941 ◽  
Vol 145 (1) ◽  
pp. 210-220 ◽  
Author(s):  
A. E. Johnson
Keyword(s):  
Carbon Steel ◽  
Creep Test ◽  
Test Piece ◽  
Creep Recovery ◽  
Creep Tests ◽  
Full Data ◽  
Working Temperature ◽  
Creep And Recovery ◽  
Generally True ◽  
Made In

Since 1876 occasional interest has been shown by investigators in the phenomenon of creep recovery, or what has been sometimes referred to as delayed elasticity or subpermanent elasticity. This may be defined as the negative strain, increasing with time, which occurs when a specimen strained under load, as in a creep test, is unloaded and maintained at its working temperature. Theories have been advanced to account for the phenomenon, but sufficiently full data have not been obtained for any of the commonly used commercial materials to provide means of checking the theories. The present paper, for the case of a 0·17 per cent carbon steel, investigates the relation between recovery and the stress, temperature, period of test, and strain, in the creep test preceding the recovery, and presents data by means of which the existing theories are compared. Creep and recovery tests were made in creep units capable of measuring creep rates of the order 10–8 in. per in. per hour, the test temperature being maintained constant to ±0·5 deg. C. At each of the temperatures 425, 455, and 485 deg. C., groups of creep tests—continued to periods of 0·2, 2, 20, and 145 hours, respectively—were made, each group consisting of tests at three different stresses. Each test piece on unloading was allowed to recover for 100 hours. One or two similar tests were also made at 350 and 550 deg. C. In addition, at 425, 455, and 485 deg. C., groups of creep tests were made, and were carried to the stage of minimum creep rate; the test piece was then unloaded, and allowed to complete its recovery. These groups of tests also consisted of tests at two or three stresses. The author discusses the relation of creep recovery to stress, temperature, period of creep, and strain in the initial creep test, and finally tabulates his principal conclusions which, he points out, apply only to the steel tested, and are not to be taken as generally true for other materials. A bibliography is also included in an Appendix.

Creep, Recovery, and Permanent Set for GR‐S and Hevea

1948 ◽  
Vol 19 (5) ◽  
pp. 456-463 ◽  
Author(s):  
S. D. Gehman
Keyword(s):  
Creep Recovery ◽  
Permanent Set

Creep Recovery of Commercially Pure Copper

1968 ◽  
Vol 10 (1) ◽  
pp. 24-35 ◽  
Author(s):  
J. Henderson ◽  
J. D. Snedden
Keyword(s):  
Creep Strain ◽  
Creep Test ◽  
Recovery Time ◽  
Empirical Equation ◽  
Pure Copper ◽  
Creep Recovery ◽  
Recoverable Strain ◽  
Commercially Pure ◽  
Commercially Pure Copper

Tension and torsion creep recovery tests on commercially pure copper at 150, 200 and 250°C are reported. Recoverable strain can range from a negligible percentage to approaching 100 per cent of the total creep strain developed, depending on stress, creep period preceding unloading, and current recovery time. An empirical equation relating creep recovery to these characteristics of the initial creep test is given.

Creep Life Prediction of T91/12Cr1MoV Dissimilar Welded Joint

2013 ◽  
Vol 330 ◽  
pp. 304-309
Author(s):  
Hu Chen ◽  
Jin Dan Zhu
Keyword(s):  
Experimental Data ◽  
Creep Test ◽  
Life Prediction ◽  
Welded Joint ◽  
Test Results ◽  
Creep Life ◽  
Dissimilar Welded Joint ◽  
Creep Life Prediction ◽  
Creep Curves ◽  
Good Agreement

Based on the creep test results of T91/12Cr1MoV dissimilar welded joint at different conditions, the creep curves of this dissimilar welded joint were established by modified θ projection concept. Low stress creep life was predicted by this curve and the established creep curve shows a good agreement with the experimental data. For computation, Larson-Miller parameters method was also used in creep life forecasting of T91/12Cr1MoV dissimilar welded joint. The resu lt showed that the modified θ projection concept was more accurately in predicting the creep life than Larson-Miller parameters method in allusion to T91/12Cr1MoV dissimilar welded joint.

scholarly journals Viscoelastic creep behavior of surface- and inner-layers of sugi boxed-heart timber under various temperatures

2019 ◽  
Vol 65 (1) ◽  
Author(s):  
Andi Hermawan ◽  
Noboru Fujimoto
Keyword(s):  
Moisture Content ◽  
Creep Test ◽  
Creep Behavior ◽  
Creep Compliance ◽  
Surface Strain ◽  
Effect Of Temperature ◽  
Creep Recovery ◽  
Viscoelastic Creep ◽  
Burgers Model ◽  
Constant Moisture Content

Abstract This study was conducted to investigate the rheological behavior of sugi boxed-heart timber under constant moisture content (MC) using a cantilever creep test. The focus of the study was the effect of temperature on viscoelastic creep behavior of surface- and inner-layer specimens of the timber. The specimens with dimensions of 75 mm in length, 25 mm wide, and 3 mm thick were prepared. A cantilever creep test with an effective span of 40 mm was conducted under a constant temperature of 20, 65, 80, and 95 °C. The equilibrium moisture content (EMC) of the specimens was set to around 12% at each temperature. A load representing 20% of rupture load of the specimens at each temperature was applied to their free-end and strain gauges were bonded at the fourth span (10 mm) on the upper and bottom surfaces of the specimens. Loading and unloading duration were set for 300 and 180 min, respectively, and a four-element Burgers model was used to model the creep behavior of the timber. It was found that temperature had significant effects on the creep properties of the timber. The surface strain and creep compliance of the surface- and inner-layer specimens tended to increase as the temperature increased. Creep compliance of the surface-layer specimen was higher than that of the inner-layer specimen at each temperature. Fitting the experimental data with the Burgers model used in this study shows good agreement and it was found that elastic (instantaneous) and viscoelastic (delayed) creep compliance of all the specimens tended to increase as the temperature increased. On the other hand, the viscosity of the dashpot element of both the Maxwell and the Kelvin unit tended to decrease as the temperature increased. Although different in magnitude, the creep-recovery compliance parameters had the same tendency as the creep compliance parameters.

Hydrothermal Synthesis and Solid-State Laser Refrigeration of Ytterbium-Doped Potassium Lutetium Fluoride (KLF) Microcrystals

2020 ◽  
Author(s):  
Xiaojing Xia ◽  
Anupum Pant ◽  
Xuezhe Zhou ◽  
Elena Dobretsova ◽  
Alex Bard ◽  
...  
Keyword(s):  
Hydrothermal Synthesis ◽  
Solid State ◽  
Information Science ◽  
Point Group ◽  
Solid State Laser ◽  
Lanthanide Ions ◽  
Group Symmetry ◽  
Luminescence Spectra ◽  
Crystalline Phases ◽  
State Laser

Fluoride crystals, due to their low phonon energies, are attractive hosts of trivalent lanthanide ions for applications in upconverting phosphors, quantum information science, and solid-state laser refrigeration. In this article, we report the rapid, low-cost hydrothermal synthesis of potassium lutetium fluoride (KLF) microcrystals for applications in solid-state laser refrigeration. Four crystalline phases were synthesized, namely orthorhombic K<sub>2</sub>LuF<sub>5</sub> (Pnma), trigonal KLuF<sub>4</sub> (P3<sub>1</sub>21), orthorhombic KLu<sub>2</sub>F<sub>7</sub> (Pna2<sub>1</sub>), and cubic KLu<sub>3</sub>F<sub>10</sub> (Fm3m), with each phase exhibiting unique microcrystalline morphologies. Luminescence spectra and emission lifetimes of the four crystalline phases were characterized based on the point-group symmetry of trivalent cations. Laser refrigeration was measured by observing both the optomechanical eigenfrequencies of microcrystals on cantilevers in vacuum, and also the Brownian dynamics of optically trapped microcrystals in water. Among all four crystalline phases, the most significant cooling was observed for 10%Yb:KLuF<sub>4</sub> with cooling of 8.6 $\pm$ 2.1 K below room temperature. Reduced heating was observed with 10%Yb:K<sub>2</sub>LuF<sub>5</sub>

A new Creep Test Method for Asphalt

2010 ◽  
Vol 11 (3) ◽  
pp. 969-991 ◽  
Author(s):  
Xiaoming Huang ◽  
yuqing Zhang
Keyword(s):  
Creep Test ◽  
Test Method
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