Creep rates of spray ice

1990 ◽  
Vol 27 (2) ◽  
pp. 185-194 ◽  
Author(s):  
D. Shields ◽  
L. Domaschuk ◽  
E. Funegard
Keyword(s):  
Power Law ◽  
Constant Pressure ◽  
Creep Behaviour ◽  
Primary Creep ◽  
Control Device ◽  
Petroleum Exploration ◽  
Secondary Creep ◽  
Creep Tests ◽  
Pressure Tests ◽  
Polycrystalline Ice

Mars Island, a man-made spray ice island, was constructed in January and February 1986, and was used as a drill platform for petroleum exploration in the Alaskan Beaufort Sea. A series of pressuremeter creep tests was run in the spray ice of Mars Island in March 1986. Individual constant-pressure tests lasted up to 5 days.It is possible to compare the creep behaviour of the spray ice as interpreted from the pressuremeter tests with the creep behaviour interpreted from the island settlement records. These comparisons are made for both primary and secondary creep on the basis of conventional power law theory. The following points are of particular interest: (1) The primary creep data can be characterized using a simple power law. The exponent of time for spray ice is similar to that for solid polycrystalline ice. The exponent of stress is different for the two kinds of ice. (2) Pressuremeter tests gave secondary creep information that correlates well with the steady-rate settlement of the island. (3) Research into the possible range of primary creep parameters for spray ice is required, given that primary creep accounted for a large portion of the settlement of Mars Island. In particular, the effect of ice density on creep rates mast be resolved. (4) The pressuremeter is potentially an excellent design control device during the manufacture of future spray ice islands. The results of constant-pressure tests of 1–2 days duration could be used to check the design assumptions pertaining to the expected consolidation of the ice mass with time. Key words: spray ice, creep, artificial islands, pressuremeter, settlement.

scholarly journals Observations of the creep of polar firn

2021 ◽  
pp. 1-19
Author(s):  
Yuan Li ◽  
Ian Baker
Keyword(s):  
Total Porosity ◽  
Constant Load ◽  
Primary Creep ◽  
Secondary Creep ◽  
Micro Ct ◽  
Creep Tests ◽  
Thin Sections ◽  
Compressive Stresses ◽  
Optical Images ◽  
Before And After

Abstract Constant-load creep tests were performed at −10°C at various compressive stresses from 0.05 to 0.75 MPa on specimens taken every 10 m along a firn core extracted at Summit, Greenland in June 2017. The microstructures before and after creep testing were examined using both X-ray microtomography (micro-CT) and optical images from thin sections. An Andrade-like equation was used to describe the primary creep behavior and yielded the time exponent k of 0.17–0.76. The onset of secondary creep occurred at strains of ~0.5–3% but was sometimes not observed at all in shallow firn specimens and at stresses ⩽0.43 MPa even for strain up to 32%. For the 50–80 m firn crept at stresses ⩾0.55 MPa, secondary creep occurred at strains of 2.6 ± 0.28%, and the stress exponent, n, in Glen's law, was found to range from 4.1 to 4.6, similar to those observed for fully dense ice. Micro-CT observations of crept specimens showed that in most cases, the specific surface area, the total porosity and the structure model index decreased, while the structure thickness increased with increasing density. These microstructural characteristics are consistent with the densification of the firn. Optical images from thin sections showed that recrystallization occurred in some specimens that had undergone secondary creep.

Investigation of Tensile and Compressive Creep Behaviour of AA2050-T34 during Creep Age Forming Process

2016 ◽  
Vol 716 ◽  
pp. 323-330 ◽  
Author(s):  
Yong Li ◽  
Zhusheng Shi ◽  
Yo Lun Yang ◽  
Jian Guo Lin
Keyword(s):  
Power Law ◽  
Creep Behaviour ◽  
Primary Creep ◽  
Constitutive Modelling ◽  
Ageing Process ◽  
Forming Process ◽  
Creep Equation ◽  
Compressive Creep ◽  
Creep Stress ◽  
Creep Age Forming

The tensile and compressive creep behaviour of aluminium alloy 2050 with T34 initial temper (AA2050-T34) during creep-ageing process has been experimentally investigated and analysed in detail. Both tensile and compressive creep-ageing tests under various stress levels (ranging from 100 MPa to 187.5 MPa) have been carried out at a temperature of 155 °C for 18 hours. The results show that creep strains under tensile stresses are much larger than those under the same levels of compressive stresses and a new “double primary creep feature” with five-stage creep behaviour has been observed in the alloy during the creep-ageing tests. The conventional power-law creep equation was applied to analyse the new creep behaviour of the alloy at the steady-state creep stage. Furthermore, the power-law relationship between the applied stress and the corresponding creep strain rate was found to be effective in all creep-ageing stages of the alloy and was used for further analysis. These analyses indicate that the dislocation and diffusion mechanisms may both contribute to this new creep behaviour and may play different roles in different creep-ageing stages. Moreover, the evolution of the creep resistance or threshold creep stress of the alloy during the creep-ageing process was quantitatively investigated by the proposed relationship. These results help to not only understand the new creep behaviour of AA2050-T34 during the creep-ageing process, but also facilitate further constitutive modelling of this new creep behaviour for its creep age forming applications.

Creep Behaviour of Closed Cell Aluminium Foams from Stress Relaxation Tests

2009 ◽  
Vol 423 ◽  
pp. 131-136 ◽  
Author(s):  
B. Carcel ◽  
A.C. Carcel ◽  
P. Arrué
Keyword(s):  
Stress Relaxation ◽  
Power Law ◽  
Creep Behaviour ◽  
Solid Material ◽  
Constant Load ◽  
Creep Tests ◽  
Closed Cell ◽  
Power Law Exponent ◽  
Order Of Magnitude ◽  
Power Law Creep

Creep behaviour of closed cell aluminium foams and transitions from power law to power law breakdown (PLB) creep regimes are investigated from results of stress relaxation tests (SRT) carried out on Alporas foams with densities between 0.20 to 0.32 g/cm3. Tests were carried out at temperatures between 200°C and 300°C and stress relaxation was measured from the collapse stress under compression of the foams. Under similar foam density, temperature and stress conditions, the values of strain rate calculated from SRT tests were of the same order of magnitude than those previously reported in the literature from conventional constant load creep tests. Under stress values close to the collapse stress, the creep mechanism seems to follow a PLB regime, with values of the power law exponent n=10-17, much higher than those corresponding to the power law creep in the solid material (n=4.4-6.5) and with activation energy values close to Q = 150 KJ/mol. Having in mind the limitations of available creep models for closed cell foams and the need for additional experimental results, the use of SRT testing would offer advantages for the assessment of the high temperature behaviour of aluminium foams, due to its lower testing times and reduced experimental effort.

Creep Behavior for Alloy 617 in Air at 950°C

2010 ◽  
Vol 654-656 ◽  
pp. 508-511 ◽  
Author(s):  
Woo Gon Kim ◽  
Song Nan Yin ◽  
Gyeong Geon Lee ◽  
Yong Wan Kim
Keyword(s):  
Creep Behavior ◽  
Primary Creep ◽  
Secondary Creep ◽  
Creep Tests ◽  
Alloy 617 ◽  
Very High Temperature Reactor ◽  
Creep Curves ◽  
High Temperature Reactor ◽  
Very High ◽  
Cr2o3 Layer

Creep behavior for Alloy 617, which is considered as one of the major structural materials of a very high temperature reactor, was investigated in air at 950oC. Creep experimental data was obtained by a series of creep tests with different stress levels at 950oC. Alloy 617 revealed little primary creep strains and unclear secondary creep stages. A tertiary creep stage was initiated from a low strain level and was dominant in full creep curves. The creep constants of A, n, m, and C in Norton’s power law and Monkman-Grant relationships were determined. In microstructure observations of crept specimens, it was found that a Cr2O3 oxidation layer was formed on the surface, and just beneath the Cr2O3 layer, an internal Al-oxide sub layer was formed with rod shapes. Also, below the internal sub layer, a thick carbide-depleted zone was developed due to reaction of the chromia and carbide precipitates. The thickness of the outer Cr-oxide layer increased with increasing creep rupture times. The increasing tendency showed a smooth slope like a parabolic curve.

scholarly journals On the time-temperature equivalency in green wood: Characterisation of viscoelastic properties in longitudinal direction

Holzforschung ◽  
2009 ◽  
Vol 63 (3) ◽  
Author(s):  
Jana Dlouhá ◽  
Bruno Clair ◽  
Olivier Arnould ◽  
Petr Horáček ◽  
Joseph Gril
Keyword(s):  
Power Law ◽  
Viscoelastic Properties ◽  
Creep Behaviour ◽  
Longitudinal Direction ◽  
Temperature Dependency ◽  
Arrhenius Law ◽  
Degree Polynomial ◽  
Creep Tests ◽  
Softening Effect ◽  
Green Wood

Abstract Aiming at modelling tree mechanics, viscoelastic properties of green wood along fibres was investigated through a sequence of creep tests in the temperature range of 30°C–70°C. The apparent validity of time-temperature equivalency was questioned by discrepancies evidenced in the approximated complex plane (ACP). This paradox was solved by assuming that the temperature not only accelerates the viscoelastic processes but also slightly increases their intensity. This softening effect of the temperature on the compliance was described by a 2nd degree polynomial. Time-temperature dependency fitted very well to the Arrhenius law up to 60°C. Based on the ACP, the power law was proposed for modelling creep behaviour in green wood. The method was successfully used for all specimens investigated.

Shape of creep curves in frozen soils and polycrystalline ice

1987 ◽  
Vol 24 (4) ◽  
pp. 623-629 ◽  
Author(s):  
Anatoly M. Fish
Keyword(s):  
Constitutive Equation ◽  
Creep Strain ◽  
Failure Time ◽  
Frozen Soil ◽  
Time To Failure ◽  
Secondary Creep ◽  
Creep Failure ◽  
Creep Tests ◽  
Creep Curves ◽  
Polycrystalline Ice

A new method was developed for determining creep parameters, particularly the time to failure, from a single linear plot in which an individual creep curve forms a straight line for primary and tertiary creep. Secondary creep is considered to be a principal point on this line that predetermines the onset of failure. The times to failure can be predicted even when creep tests are not complete by extrapolating information obtained for primary creep. Based upon T. H. Jacka's test data, prediction of creep strain was evaluated using the constitutive equation of A. M. Fish for entire creep and compared with the modified Sinha equation of M. F. Ashby and P. Duval for attenuating creep as well as with models for primary and secondary creep. It is shown that the shape of the creep curves, and thus the creep parameters, varies with stress, temperature, and other factors. Hence, a family of creep curves cannot be described by a constitutive equation with a single set of creep parameters that do not take into account these variations without loss in the accuracy of the creep strain calculations. Key words: frozen soil, polycrystalline, ice, creep, failure, time to failure, attenuation, constitutive modelling.

The Role of Interfacial Precipitates on Creep Behaviour of Power Metallurgy (PM) Ti-48Al-2Cr-2Nb+1W Alloy

2010 ◽  
Vol 654-656 ◽  
pp. 496-499 ◽  
Author(s):  
Dong Yi Seo ◽  
Scott Bulmer ◽  
H. Saari ◽  
Han Liang Zhu ◽  
Peter Au
Keyword(s):  
Creep Resistance ◽  
Creep Behaviour ◽  
Hot Isostatic Pressing ◽  
Lamellar Microstructure ◽  
Primary Creep ◽  
Nominal Composition ◽  
Controlled Cooling ◽  
Creep Tests ◽  
Fully Lamellar

Pre-alloyed powders with a nominal composition of Ti-48Al-2Cr-2Nb+1W were consolidated by hot isostatic pressing (HIP). After the HIP process, a step cooled heat treatment (SCHT) with a carefully controlled cooling rate was applied to homogenize the HIP’ed microstructure and produce a fully lamellar microstructure. Following the SCHT, various isothermal aging at 950 °C and step aging processes form interfacial precipitates at the lamellar interfaces. The morphology, size, and distribution of the precipitates are dependent on the aging condition. Creep tests were carried out in air at 760 °C and 276 MPa to investigate the effect of interfacial precipitates. Primary creep resistance and creep life of the 8 and 144 hr aged conditions are improved substantially compared to the unaged condition due to the existence of the interfacial precipitates. However, the step aging process improves the creep resistance only slightly, probably because of the size and distribution differences of the interfacial precipitates compared to the 144 hr aged condition. Microstructure control is important since it has a substantial influence on creep behavior, especially primary creep resistance.

Contribution of Primary Creep in Modeling the Mechanical Behavior of Polycrystalline Ice

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
G. Aryanpour ◽  
M. Farzaneh
Keyword(s):  
Mechanical Behavior ◽  
Primary Creep ◽  
Experimental Results ◽  
Secondary Creep ◽  
Inelastic Behavior ◽  
Viscoplastic Deformation ◽  
Polycrystalline Ice

In most of the models proposed for deformation of ice, in addition to instantaneous elastic and viscoelastic parts, a viscoplastic part is also considered. An expression used for material secondary creep is usually employed to describe the viscoplastic component. In this study, however, another viscoplastic deformation of primary creep type is also considered in addition to the secondary creep. Therefore the permanent contribution of deformation is suggested to consist of primary and secondary creep parts. The existence of the primary creep contribution is investigated and characterized by using experimental results reported in the literature. The identified primary creep contribution is then validated by other available experimental results. Finally, the significance of primary creep in the inelastic behavior will be discussed.

Creep of TiAl alloys at 750°C under moderate stress

2004 ◽  
Vol 842 ◽  
Author(s):  
Alain Couret ◽  
Joel Malaplate
Keyword(s):  
Powder Metallurgy ◽  
Creep Behaviour ◽  
Secondary Creep ◽  
Creep Tests ◽  
Dislocation Mechanism ◽  
Tial Alloys ◽  
Creep Properties ◽  
Moderate Stress

ABSTRACTThe creep properties at 750°C of TiAl alloys produced by cast and powder metallurgy processes are investigated by creep tests and subsequent TEM investigations. It is demonstrated that the same dislocation mechanism is controlling the primary and secondary creep stages in these two alloys. This mechanism is the mixed climb of ordinary dislocations. Explanations to the creep behaviour during primary and secondary stages are then proposed.

scholarly journals Anelastic Behaviour of Polycrystalline Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 621-628 ◽  
Author(s):  
Paul Duval
Keyword(s):  
Creep Behaviour ◽  
Transient Creep ◽  
Time Dependent ◽  
Internal Stresses ◽  
Creep Recovery ◽  
Creep Tests ◽  
Small Temperature ◽  
Polycrystalline Ice ◽  
Glacier Ice ◽  
Relationship Of

Abstract Torsion creep tests were performed on glacier ice at temperatures above -12°C. The polycrystalline ice, when unloaded, exhibits creep recovery. The time-dependent recoverable component of deformation (or anelastic strain) ϵa was found to be adequately described by a relationship of the form: ϵa = Δτ log(r + αt)/h, where Δτ is the stress decrement, α a constant, and t the time. The anelastic modulus h defined for times t in excess of 3 h is always smaller than the dynamic elastic modulus. The movement of dislocations composing the sub-boundaries or in dislocation pile-ups may produce this important reversible deformation. The time-dependent recovery is explained in a similar way to the transient creep behaviour observed at low temperatures for metals. The small temperature dependence of creep recovery would arise from the existence of a distribution of internal stresses values.

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