STRAIN LOCALIZATION IN CYCLIC DEFORMATION AND HOW ENVIRONMENTS AFFECT IT

摘要

An overview is provided of some 20 years of research into the effects of benign and aggressive environments on cyclic deformation and fatigue. The focus is on single crystal experiments in which the environments have been carefully controlled. Although there is often little effect of the different environments on macroscopic indications of the cyclic deformation, such as the flow stress, it is shown that the extent of localized strain varies greatly depending on the environments. Benign environments, such as vacuum, by inhibiting crack initiation, cause strain delocalization and thereby enhance life still further. Aggressive environments, whether gaseous or liquid and capable of either dissolution or oxidation, generally increase strain localization with adverse effects on life. The imposition of passivity affects fatigue behavior no worse than normal air. It is argued that the conclusions obtained from single crystal work can be extended to polycrystalline metals, to wavy and planar slip metals and (with caution) to commercial metals, even those in strongly hardened conditions. The roles of hydrogen or embrittlement processes in fatigue are not treated here.