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See detailTransient yielding during compression tests on ECAP’ed AA1050 Aluminium
Verlinden, Bert; Chen, Enze; Duchene, Laurent ULg et al

in Materials Science Forum (2011), 667-669

In most papers dealing with tension and/or compression tests, the conventional yield stress is determined either by an offset method (usually 0.2% strain) or by back extrapolation from the stress-strain ... [more ▼]

In most papers dealing with tension and/or compression tests, the conventional yield stress is determined either by an offset method (usually 0.2% strain) or by back extrapolation from the stress-strain curve. In our experiments on ECAP‟ed Aluminium a transient hardening saturation (THS) is always observed during the compression tests, but not during the tensile tests. This THS occurs at a significantly lower stress than the conventional yield stress. The aim of the present paper is to determine which the “real” start of yielding is. Two different experimental approaches have been adopted, confirming that the THS stage is exactly the yielding stage. This is not unimportant because it increases the tension-compression asymmetry and hence the back-stress and kinematic hardening. The reason for this different behaviour between tension and compression can be ascribed to a different change in strain path with respect to the ECAP deformation. [less ▲]

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See detailPrediction of the Tension/Compression asymmetry of ECAP processed FCC material using an integrated model based on dislocation and back-stress
Chen, Enze; Duchene, Laurent ULg; Habraken, Anne ULg et al

in Materials Science Forum (2011), 667-669

In our recent work, a new integrated model was proposed to describe the back-stress evolution based on the dislocation substructure and texture. By relating the back-stress to the dislocation density in ... [more ▼]

In our recent work, a new integrated model was proposed to describe the back-stress evolution based on the dislocation substructure and texture. By relating the back-stress to the dislocation density in cell walls and in the cell interior, this model is able to capture the back-stress evolution of ECAP processed pure aluminium. In this paper, the model is used for another FCC material, namely copper. The aim is to check whether this model is able to predict the tension/compression asymmetry (due to the back-stress) of copper. The results show that this is indeed the case and it is also found that the strain rate ratio proposed in our previous work [1] is a function of the dislocation density ratio. [less ▲]

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