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Characteristics of serrated flow, specifically of stress-drops, were measured for a f.c.c. solid-solution aluminum alloy and a b.c.c. mild steel. Both materials behave in a similar way, exhibiting an increase in the stress-drop rate when the magnitude of the stress-drop increases. This dependence is distinctly strain-dependent: at lower strains the drop rate at a given stress-drop is larger than at higher strains. For both materials, these strain dependences saturate at high strain levels. The stress-drop rates at a given stress-drop are temperature-dependent at all values of strain for the aluminum alloy, but in the case of the mild steel they become temperature-dependent at high strain levels, i.e. in the saturated condition. These differences can be explained in terms of thermally activated deformation effects. Activation enthalpies calculated from these temperature dependences are in reasonable agreement with those predicted for dislocation motion in these materials. |
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