On PLC Band Propagation Velocity under Stress-Controlled Tests in Aluminum Alloys
Plastic flow of solid solutions, particularly lightweight alloys, is unstable within a certain regime of temperature, ageing and loading rates. This instability of strain rate softening type is associated with dynamic strain ageing due to the interaction between mobile dislocations and clouds of impurities and is characterized by the appearance of serrations (respectively strain bursts) when testing is performed at constant strain rate (respectively constant stress rate). Each serration or strain burst corresponds to the localization of deformation in a band which may propagate along the tensile specimen. To investigate the effect of testing conditions on band propagation velocity, tensile tests were carried out with a soft machine (constant stress rate) on two aluminium alloys of the 5000 and 7000 series. It is important to note that a decrease of band propagation velocity with increasing stress rate was observed for different temperatures and ageing. This trend is well predicted by a recent model proposed by Hähner.
Keywordsplastic instability dynamic strain ageing band propagation velocity soft tensile machine aluminum alloy
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