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Submitted on 1 Jan 1971
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MODULUS CHANGES IN STRAIN-CYCLED COPPER
R. den Buurman
To cite this version:
R. den Buurman. MODULUS CHANGES IN STRAIN-CYCLED COPPER. Journal de Physique
Colloques, 1971, 32 (C2), pp.C2-144-C2-144. �10.1051/jphyscol:1971229�. �jpa-00214555�
JOURNAL DE PHYSIQUE Colloque C2, supplbment au no 7, tome 32, Juillet 1971, page C2-144
MODULUS CHANGES IN STRAIN-CYCLED COPPER
R. D E N BUURMAN
Laboratoriurn voor Metaalkunde Technische Hogeschool Delft, Nederland This work is part of the research programme
of the foundation F. 0. M., sponsored by Z. W. 0.
Abstract.
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The shear modulus (G) of copper is heavily reduced by cold working at low tem- peratures as has been shown by Druyvesteyn et al. [l]. The effect, the so-called AG-effect, was attributed to dislocations introduced by the deformation as described by Mott [2] and Friedel [3].When an elastic stress is applied, the dislocations bow out in their glide planes causing an extra elastic strain and thus a decrease of the modulus. This modulus defect was reduced by annealing at higher temperatures which was ascribed to the pinning of dislocations by point defects. Many investigators studied these effects after unidirectional deformation [4] but analogous studies on cyclically deformed materials are much less numerous.
In the present work the decrease of the shear modulus due to strain controlled cyclic torsion was measured on rods of polycrystalline pure copper cycled at various amplitudes.
After some 5 X 104 cycles at 78 OK, G reached a saturation value qualitatively in accordance with for instance the behaviour of the flow stress vs. number of cycles in fatigued metals. The saturation value of
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AG/G increased with strain amplitude up to about 4 % for a strain ampli- tude of 4.2 X 10-4. The isochronal recovery behaviour was analogous to that observed after unidirectional deformation. Three discrete steps were present, called IIa, IIb and I11 centered at 133 OK, 193 OK and 273 OK respectively. After cyclic deformation step I11 was considerably smaller.Cycling at room temperature and at 78 OK caused about the same AG-effect, if measured at 78 OK.
As the point defects produced by the deformation are mobile at room temperature, this implies that point defect pinning does not occur when the dislocations move to and fro during cyclic deformation. The dependence of the modulus effect on the measuring temperature is in accor- dance with the observations of Druyvesteyn and Blaisse [5] after unidirectional deformation.
References
[l] DRUYVESTEYN (M. J.), SCHANNEN (0. F. Z.), SWA- [4] VAN DEN BEUKEL (A.), in : Vacancies and Interstitials
VING (E. C. J.), Physica, 1959, 25, 1271. in Metals, North Holland, 1970.
[2] MOTT (N. F.), Phil. Mag., 1952, 43, 1151. [5] DRUYVESTEYN (W. F.), BLAISSE (B. S.), Physica, 1962, [3] FRIEDEL (J.), Phil. Mag., 1953, 44, 444. 28, 695.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971229
