Negative work-hardening rates areprecursors of plastic instabilities. The objective ofthe work is to determine the origin of the stressdecrease in the case of prestrained sheet metals.Samples of lox carbon steel and pure aluminium deformedin rolling and reloaded in simple shear exhibitsoftening for specific shear directions with respect tothe rolling direction. Structural and texturalevolutions are analysed with transmission electronmicroscopy and X-ray measurements, respectively. Thelow carbon steel shows clear evidence of intragranularstructural destabilization while the Taylor factor,estimated by self-consistent calculations, remainsnearly constant, It is deduced that for steel, thesoftening has a structural origin. By contrast thealuminium samples present identical structural changeswhatever the sign of the work-hardening rate. It is shownthat the latter is strongly correlated with Taylorfactor evolution. A textural instability is obtained in this case.
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