About the determination of the thermal and athermal stress components from stress-relaxation experiments

Published on Feb 1, 2008in Acta Materialia8.203
· DOI :10.1016/J.ACTAMAT.2007.09.027
Tomáš Kruml23
Estimated H-index: 23
,
O. Coddet5
Estimated H-index: 5
,
Jean-Luc Martin18
Estimated H-index: 18
(École Polytechnique)
Sources
Abstract
The determination of the thermal and athermal stress components using relaxation experiments along a stress-strain curve is critically evaluated. Short-term stress-relaxations are performed along the stress-strain curve of single crystals of Ge at 850 K, Cu, and Ni3Al at 300 K. They are analyzed by three different equations with two or three parameters including the athermal stress. The stress components obtained are compared to the values determined by stress-reduction experiments considered as the reference method. The relaxation rate is considered successively to be a power function or a hyperbolic sine function of the effective stress or a hyperbolic decrease of stress with time is assumed. It is shown that the three methods overestimate or underestimate the stress components depending on the material and deformation conditions. The error can be as large as about 100%. Reasons for the inadequacy of short-term relaxation experiments for the determination of the stress components are discussed. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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References21
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#1Zdeněk Drozd (Charles University in Prague)H-Index: 9
#2Zuzanka Trojanová (Charles University in Prague)H-Index: 20
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Metal matrix composites LA40 and LA43 were deformed in compression. Sequential stress relaxation tests were performed at temperatures from RT up to 200 °C. The duration of the stress relaxation tests was 300 s. The internal stress was determined from the stress relaxation curves using a computer fitting. The results show that the internal stress represents a substantial part of the applied stress. The possible components of the internal stress are discussed.
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#1Tomáš KrumlH-Index: 23
#2Corinne Dupas (École Polytechnique)H-Index: 4
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Abstract The issue concerning possible dislocation multiplication laws before the upper yield point of covalent materials is approached in 〈123〉 oriented Ge single crystals using the technique of stress relaxation and transient creep tests. Unlike in metals, relaxation tests exhibit a linear decrease of stress with time and inverse creep is observed. It is shown that these features are the signature of multiplication processes during the transient tests. Attempts at interpreting such particular ...
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#1S. Van PetegemH-Index: 30
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Stress reduction experiments performed during tensile deformation of nanocrystalline electrodeposited Ni demonstrate high values for the effective and the internal stress as compared to coarse grained metals and evidence the existence of a negative creep. The results are interpreted in terms of a thermally activated dislocation mechanism where propagation is hindered by pinning at grain boundaries.
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Abstract Repeated stress relaxation tests and strain rate jump tests have been carried out over a range of deformation temperatures (77–373 K) on electrodeposited nanocrystalline Ni with an average grain size of ∼30 nm. The strain rate sensitivity, the apparent and physical activation volume, and the activation energy have been determined. The magnitude observed for these characteristic deformation parameters, as well as their temperature-dependent behavior, is very different from those of coars...
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Abstract Stress reduction experiments have been performed during constant strain-rate compression tests of single crystals of Ge, Cu, CuAl solid solutions and Ni3Al. These tests allow one to separate the components of the applied stress. They provide useful information about the spatial oscillation of the internal stress, the influence of temperature and strain-rate on the internal and the effective stresses. Activation volume values can be obtained and the Cottrell – Stokes behavior can be chec...
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This review presents various examples of transient mechanical tests and their interpretation. Logarithmic relaxation experiments are analyzed by various methods. The advantages of repeated relaxation and creep experiments are emphasized.
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