Cyclic Work Hardening of Al Single Crystal (Bauschinger Effect)
1975 Volume 24 Issue 266 Pages 1065-1071
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1975 Volume 24 Issue 266 Pages 1065-1071
The main objectives of the present study are to make clear the mechanism of the cyclic work hardening of a single crystal and to simulate the stress-strain relation in the rapid hardening region as well as in the saturated hardening region. To achieve these purposes, the stress-strain relation of an Al single crystal was determined in a cyclic total strain controlling system. This paper deals and discusses how the Bauschinger effect depends on the crystal orientation factor and how the slip deformation differs between the two hardening regions.
The results are summarized as follows.
(1) Bauschinger strain γβ increased in proportion to pre-applied stress τF. That is, the Bauschinger effect decreased gradually with increasing the strain amplitude, and its rate depended on the crystal orientation, The Bauschinger effect decreased with increasing the number of cycles until its strain reached a constant value. In these ways, the Bauschinger effect is related to the condition of slip system motions.
(2) For reversing of stress direction, the decrease of yield stress τB(=τF-|τR|) was formulated as
τB=k·γFm
where the Bauschinger exponent m depended on the crystal orientation and it was constant for each crystal until γR(0.01), or the plastic strain at τR=0, reached 0.01%. Then beyond this value, m increased with γR. With the increase of the number of cycles, the dependence of constant value m in these region on the crystal orientation became less.
(3) In the rapid hardening region, the amount of the primary slip system became more pronounced as the cummulative strain increased. But in the saturated hardening region, the change in the amount of slip could not be observed even though the loading direction was reversed. In this region, the flip-flop motion of dislocations is considered to play a main role in primary slip system. On the secondary slip system, however, the slip motion was observed clearly. But during the tension to the compression process, the loci of slip motion were irreversible and were unsymmetrical due to the secondary slip in other slip systems.
