An Interpretation of the Haasen-Kelly Effect
Résumé
In 1957, P. Haasen and A. Kelly presented an account of experiments which showed that in Al and Ni single crystals the mere act of unloading during a tensile test caused a small but reproducible transient increase in flow stress, a 'yield-point'. The increase is proportional to the current work-hardened stress level. It occurs at the lowest temperatures, where diffusion is not possible, but it is enhanced at higher temperatures. The effect was interpreted as arising from dislocations which 'anchor themselves during unloading and that this process of anchoring, which prevents reverse plastic flow, is also responsible for the yield-point effect on reloading'. Recent ideas emphasising the role of dislocation dipoles as sources for slip provide a natural explanation for these effects.
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