The Effect of Deformation Temperature on the Bauschinger Effect in Polycrystalline Aluminium

Upon reversed straining of a pre-strained aluminium at high temperatures, there appears a strain region where plastic deformation proceeds at an approximately constant stress level, and the subgrain structures developed by pre-straining become loosened once and then new subgrain structures characteristic of the reversed straining are formed. In the present experiment polycrystalline aluminium specimens were subjected to a special type of cyclic straining at high temperatures where such a strain region appears.The amount of strain and the stress level in such a strain region and the ratio of the yield stress upon stress reversal to the pre-stress level decreased with the progress of the cyclic straining. These facts suggest that the stability of dislocation structures upon stress reversal gradually increases, that is, the tendency to undergo changes due to the stress reversal is reduced as the cyclic straining progresses. Transmission electron microscopy showed that the increase in the stability of dislocation structures is caused by the decrease in density of isolated dislocations and also by the change of sub-boundaries from an unstable ill-defined state to a stable well-defined one.

show abstract

“…A detailed description of the machine has been given in a previous paper (20) Mechanical testings were carried out at 458…”

Section: Methodsmentioning

confidence: 99%

“…Although the grain size was rather large, no problems were found in studying the Bauschinger effect on aluminium (20). Moreover, this size was suitable for X-ray examination (19).…”

Section: Methodsmentioning

confidence: 99%

Change in Dislocation Structure during Cyclic Straining of Polycrystalline Aluminium at High Temperatures

et al. 1978

Self Cite

View full text Add to dashboard Cite

show abstract

“…were done at temperatures between 293 and 773K under nominal strain rates of the order of 10-4s-1 with an Instron-type machine modified for tension-compression cyclic loading. A detailed description of the machine has been given in a previous paper (7).…”

Section: The Modelmentioning

confidence: 99%

“…However, it was found in comparison between zinc and an aluminium-4 mass% copper alloy containing θ'or θ precipitates that the deviation from the elastic behaviour at a higher stress during unloading does not necessarily lead to a larger Bauschinger strain (6). Further, when different parameters obtained at an earlier or later stage of reversed deformation were used, different conclusions were drawn on temperature- (7) and orientation- (8) dependences of the effect. These facts suggest that, for a complete understanding of the effect, the whole shape of the stressstrain curve in the reversed direction (the Bauschinger curve) must be taken into consideration.…”

Section: Introductionmentioning

confidence: 98%

A Unified Representation of Stress-Strain Curves in Reversed Direction of Prestrained Cell-Forming Metals

1986

Self Cite

View full text Add to dashboard Cite

A model of the Bauschinger effect for cell-forming metals is summarized, in which a strain in the reversed direction is caused by "unpiling" of dislocations dynamically piled up in the cell interior during prestraining. The model suggests that, if both stress,σ, and strain,εr, in the reversed direction are normalized by the prestress, σP, σ/σp vs εr/σp curves become coincident with one another.Except after prestraining to small strains(<-3%), the normalization byσp was found to be applicable to changes in prestrain and grain size in room-temperature deformation of aluminium and copper, the normalized curves for different prestrains and grain sizes becoming similar in shape. This indicates that the present model can explain the Bauschinger effect so far as the cell structure forms during prestraining.However, the normalization by σp/μ(u:the shear modulus)failed for changes in deformation temperature and stacking-fault energy, namely for a change in the nature of dislocation structure (that is, for the conversion of cell structure to subgrain structure or to planar arrays of dislocations). For presenting a more widely applicable model, a quantitative change in a ratio of the number of dynamically stored dislocations during prestraining to that of total dislocations (namely, a fraction of reversely mobile dislocations) with dislocation structure must be taken into consideration.

show abstract

“…In all cases the initial loading was in the tensile direction. A detailed description of the machine has been given in a previous paper (1). Mechanical testings were carried out under a strain rate of at room temperature.…”

Section: Mechanical Testmentioning

confidence: 99%

Orientation Dependence of the Bauschinger Effect in Aluminium Single Crystals

et al. 1977

Self Cite

View full text Add to dashboard Cite

In order to study the orientation dependence of the Bauschinger effect, compressive flow behaviour of aluminium single crystals with various orientations prestrained in tension up to g/mm2 shear stress on the primary slip plane) was investigated at room temperature. Several kinds of parameters to evaluate the Bauschinger effect in terms of the stress, strain and energy were measured at various stages of the reversed straining.The parameters determined at relatively early stages of the reversed straining decreased with increase in the Schmid factor for the primary slip system. On the other hand, the parameters obtained at later stage showed a different orientation dependence. These results support the conclusion, given in a previous paper, that one should be very careful in comparing the results by different authors.It is generally accepted at the present stage of investigation that the Bauschinger effect originates from the elastic interactions among dislocations introduced during prestraining. Hence, the parameters determined at early stages may be more suitable for the estimation of the direct influence of dislocation structures due to prestraining on the Bauschinger effect. Moreover, optical microscopy of specimen surfaces after prestraining showed that the glide on the secondary slip planes occurred more frequently in crystals with lower Schmid factors. On these bases the Bauschinger effect may be concluded to decrease with an increase of the Schmid factor, that is, the effect is smaller in crystals oriented for a single glide than in those oriented for multiple glide. Such orientation dependence of the effect may be explained in terms of the change in and l are the density and the mean path of dislocations which move back upon the stress reversal, respectively.

show abstract

The Effect of Deformation Temperature on the Bauschinger Effect in Polycrystalline Aluminium

Cited by 17 publications

References 15 publications

Change in Dislocation Structure during Cyclic Straining of Polycrystalline Aluminium at High Temperatures

Change in Dislocation Structure during Cyclic Straining of Polycrystalline Aluminium at High Temperatures

A Unified Representation of Stress-Strain Curves in Reversed Direction of Prestrained Cell-Forming Metals

Orientation Dependence of the Bauschinger Effect in Aluminium Single Crystals

Contact Info

Product

Resources

About