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.

Computational and Experimental Characterization of Indentation Creep

2003 ◽  
Vol 795 ◽  
Author(s):  
Ming Dao ◽  
Hidenari Takagi ◽  
Masami Fujiwara ◽  
Masahisa Otsuka
Keyword(s):  
Finite Element ◽  
Power Law ◽  
Constant Load ◽  
Dislocation Creep ◽  
Solid Solution Alloy ◽  
Indentation Creep ◽  
Creep Tests ◽  
Uniaxial Creep ◽  
Self Similar ◽  
Power Law Creep

ABSTRACT:Detailed finite-element computations and carefully designed indentation creep experiments were carried out in order to establish a robust and systematic method to accurately extract creep properties during indentation creep tests. Finite-element simulations confirmed that, for a power law creep material, the indentation creep strain field is indeed self-similar in a constant-load indentation creep test, except during short transient periods at the initial loading stage and when there is a deformation mechanism change. Self-similar indentation creep leads to a constitutive equation from which the power-law creep exponent, n, the activation energy for creep, Qc and so on can be evaluated robustly. Samples made from an Al-5.3mol%Mg solid solution alloy were tested at temperatures ranging from 573 K to 773 K. The results are in good agreement with those obtained from conventional uniaxial creep tests in the dislocation creep regime.

The stress relaxation and creep behaviour of a manganese-stabilized austenitic stainless steel

2009 ◽  
Vol 44 (3) ◽  
pp. 201-209 ◽  
Author(s):  
A Pagliarello ◽  
J Beddoes
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Stress Relaxation ◽  
Creep Strain ◽  
Creep Behaviour ◽  
Constant Load ◽  
Relaxation Behaviour ◽  
Creep Tests ◽  
Stress Strain ◽  
The Difference

The stress relaxation behaviour of 21–4N, a manganese-stabilized austenitic stainless steel, is investigated in terms of the metallurgical state, the application of multiple strain levels during ‘stepped’ stress relaxation testing at 700 °C, the strain level during isostrain stress relaxation tests at 538 °C and 700 °C, and the correspondence with results from constant-load creep tests. The results indicate that for isostrain stress relaxation tests the stress relaxation rate is similar for strains that span both elastic and plastic strain levels. A transition in the stress relaxation behaviour occurs at a stress level approximately equivalent to the tensile stress–strain proportional limit; below this transition the stress–strain rate relationship, or the time predicted for 1 per cent creep strain, obeys a creep power law type of equation. Stress relaxation testing successfully delineates the difference between the creep resistances of two different metallurgical conditions with similar tensile properties using fewer specimens and requiring less time. The time to 1 per cent creep strain determined from the analysis of stress relaxation results is always less than the actual time to 1 per cent creep strain during constant-load creep tests.

High-Temperature Creep Tests of Two Creep-Resistant Materials at Constant Stress and Constant Load

2019 ◽  
Vol 827 ◽  
pp. 246-251
Author(s):  
Vàclav Sklenička ◽  
Květa Kuchařová ◽  
Marie Kvapilová ◽  
Luboš Kloc ◽  
Jiří Dvořák ◽  
...  
Keyword(s):  
Creep Behaviour ◽  
Constant Load ◽  
Complex Stress ◽  
Constant Stress ◽  
Fracture Mechanisms ◽  
Stress Tests ◽  
Creep Tests ◽  
Deformation And Fracture ◽  
Dependent Component ◽  
The Difference

Creep is defined as a time dependent component of plastic deformation. Creep tests can be performed either at constant load or at constant applied stress. Engineering creep tests carried out at constant load are aimed at determination of the creep strength or creep fracture strength, i.e. the data needed for design. The constant stress tests are important as a data source for fundamental investigations of creep deformation and fracture mechanisms and for finite element modelling of more complex stress situations. For some materials, the difference between the two type of testing can be very small, while for other materials is large, depending on the creep plasticity of the material under testing. The paper aims to compare the creep results of two different creep-resistant materials: the advanced 9%Cr martensitic steel (ASME Grade P91) and a Zr1%Nb alloy obtained by both testing methods and to clarify the decisive factors causing observed differences in their creep behaviour.

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.

A Study of Deformation Mechanism During Nanoindentation Creep in Tin-Based Solder Balls

2006 ◽  
Vol 129 (1) ◽  
pp. 71-75 ◽  
Author(s):  
Tadahiro Shibutani ◽  
Qiang Yu ◽  
Masaki Shiratori
Keyword(s):  
Strain Rate ◽  
Power Law ◽  
Early Stage ◽  
Stress Sensitivity ◽  
Nanoindentation Test ◽  
Diffusion Creep ◽  
Creep Tests ◽  
Diffusive Flow ◽  
Solder Balls ◽  
Power Law Creep

As the shrinkage and integration of devices, the creep behavior of tin-based alloys becomes important with microscales. In this paper, the behavior of creep deformation in solder alloys during a nanoindentation test was examined. Nanoindentation creep test was carried out for tin-based solder balls. Obtained results summarized as follows: (i) The stress exponent for power-law creep estimated can be evaluated from the evolution of hardness. These values obtained in the early stage corresponds with that of bulk within the range of high strain rate. (ii) The stress sensitivity decreases after stress relaxation in nanoindentation creep tests. The saturated value is 1 in three solder balls. (iii) The morphology of indented surface consists of three parts: initial indentation, power-law creep, and granular surface. It suggests that the transition from power-law creep to diffusion creep takes place. (iv) Finite element method analysis reveals stress and strain concentration appears in the vicinity of the tip. Strain field remains self-similar as the indentation proceeds. (v) The gradient of triaxial stresses below the tip in a nanoindentation test accelerates the creep strain rate due to the diffusive flow, relatively.

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.

Analysis of Creep Curves of Haynes 230 Superalloy

2010 ◽  
Vol 638-642 ◽  
pp. 2285-2290 ◽  
Author(s):  
Maurizio Maldini ◽  
Giuliano Angella ◽  
Valentino Lupinc
Keyword(s):  
Applied Stress ◽  
High Temperatures ◽  
Creep Curve ◽  
Creep Behaviour ◽  
Strong Dependence ◽  
Solution Treatment ◽  
Constant Load ◽  
Creep Tests ◽  
Haynes 230 ◽  
Creep Curves

The creep behaviour of the solid solution strengthened nickel-based superalloy Haynes 230 has been investigated under constant load and temperature conditions on as received, after conventional solution treatment, and on overaged conditions. The experimental results have shown a very strong dependence of the creep curve shape with the applied stress/temperature: in the tests performed at high stresses/low temperatures, the primary/decelerating stage takes an important portion of the creep curve. At these test conditions, the accelerating creep is mainly caused by the increase of the applied stress with the strain as it happens in constant load creep tests. In the tests performed at low stresses/high temperatures, the primary stage is very small and the following accelerating creep is characterized by different accelerating creep stages. The analysis of the creep curves on the as received and overaged alloys, has shown that a large portion of the accelerating creep at low stresses/high temperatures is caused by microstructural instability.

scholarly journals On the identification of power-law creep parameters from conical indentation

2021 ◽  
Vol 477 (2252) ◽  
pp. 20210233
Author(s):  
Yupeng Zhang ◽  
Alan Needleman
Keyword(s):  
Stress Relaxation ◽  
Stress Exponent ◽  
Power Law ◽  
Exponential Factor ◽  
Creep Stress ◽  
Uniaxial Creep ◽  
Creep Stress Exponent ◽  
Power Law Creep ◽  
Good Agreement ◽  
Conical Indentation

Load and hold conical indentation responses calculated for materials having creep stress exponents of 1.15, 3.59 and 6.60 are regarded as input ‘experimental’ responses. A Bayesian-type statistical approach (Zhang et al. 2019 J. Appl. Mech. 86 , 011002 ( doi:10.1115/1.4041352 )) is used to infer power-law creep parameters, the creep exponent and the associated pre-exponential factor, from noise-free as well as noise-contaminated indentation data. A database for the Bayesian-type analysis is created using finite-element calculations for a coarse set of parameter values with interpolation used to create the refined database used for parameter identification. Uniaxial creep and stress relaxation responses using the identified creep parameters provide a very good approximation to those of the ‘experimental’ materials with stress exponents of 1.15 and 3.59. The sensitivity to noise increases with increasing stress exponent. The uniaxial creep response is more sensitive to the accuracy of the predictions than the uniaxial stress relaxation response. Good agreement with the indentation response does not guarantee good agreement with the uniaxial response. If the noise level is sufficiently small, the model of Bower et al. (1993 Proc. R. Soc. Lond. A 441 , 97–124 ()) provides a good fit to the ‘experimental’ data for all values of creep stress exponent considered, while the model of Ginder et al. (2018 J. Mech. Phys. Solids 112 , 552–562 ()) provides a good fit for a creep stress exponent of 1.15.

Suppression of Stress Relaxation in MEMS Multilayer Film Microstructures by Use of ALD Nanocoatings

2002 ◽  
Author(s):  
Yanhang Zhang ◽  
Martin L. Dunn ◽  
Jeffrey W. Elam ◽  
Steven M. George
Keyword(s):  
Stress Relaxation ◽  
Power Law ◽  
Multilayer Film ◽  
Atomic Layer ◽  
Relaxation Mechanism ◽  
Isothermal Hold ◽  
Thermal Cycles ◽  
Al2o3 Layer ◽  
Full Field ◽  
Power Law Creep

We study the suppression of stress relaxation in MEMS multilayer film microstructures by the use of alumina nanocoatings realized by atomic layer deposition (ALD). Gold (0.5 μm thick) / polysilicon (1.5 or 3.5 μm thick) beam and plate microstructures were fabricated by the MUMPs surface micromachining process. The microstructures were then coated on both sides with a 40 nm thick amorphous Al2O3 layer by ALD. The beam and plate microstructures were initially thermal cycled between room temperature and 190°C tostabilize the gold microstructure. After the initial thermal cycles, the microstructures were cooled from 190°C to 120°C and held at 120°C for about 2000 hours (three months). We measured, using an interferometric microscope with a custom-built temperature chamber, full-field deformed shapes (and from these determined the average curvatures in x- and y- directions) of the microstructures during the initial thermal cycles, during the cooling process from 190 °C to 120 °C, and during the isothermal hold. Measurements were made on both coated and uncoated microstructures to assess the influence of the coating. We find that while the 40 nm thick coating has a small effect on the thermoelastic response of the microstructure, it significantly reduces the extent of stress relaxation during the isothermal hold. We modeled the curvature evolution with time assuming the stress relaxation mechanism is power-law creep in the gold, ε˙ = Aσn, and that the polysilicon and alumina deform elastically. The simple model describes the observed behavior reasonably well for the uncoated microstructures (when the power-law parameters are fit using the measured curvature), however, for the coated microstructures, the model predicts a decrease in the stress relaxation, but nowhere near the magnitude observed. This suggests that not only is the stress state in the gold film altered by the nanoscale coating, but also the fundamental deformation mechanisms are altered.

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