Cyclic Deformation of Low-Carbon Iron

Abstract

<p>The mechanical behaviour and the microstructural changes preceeding fatigue fracture have been investigated in ferrous systems subjected to controlled cyclic straining. Attention has been focussed on three basic aspects of the fatigue process:</p> <p>(1) The Bauschinger Effect and the Polarisation of Plastic Flow in Single- and Two-Phase Iron-Based Alloys: the investigation involved the study of the influence of dislocation distribution on the magnitude of the Bauschinger effect, and the study of the Bauschinger effect in two-phase materials as a function of both forward strain and volume fraction of particles. The results are interpreted in terms of some of the currently available theories for the deformation in plastically inhomogeneous materials.</p> <p>(2) Fatigue Softening in Single-Phase Low-Carbon Iron: the investigation involved the study of the microstructural changes occurring in prestrained specimens during cyclic softening, and the influence of initial dislocation arrangement on the rate and extent of fatigue softening. Simple models were developed to rationalize the kinetics of fatigue softening.</p> <p>(3) Instability of Plastic Flow in Quenched-Aged Armco Iron: the investigation involved the study of the influence of various particle dispersions on the stability of plastic flow in fatigue, and the detailed microstructural features developing in fatigue which lead to the localization of plastic flow and onset of fatigue cracks. The problem of instability has been rationalized, macroscopically, in terms of the mechanical equation of state, and microscopically, in terms of the detailed structure of the localized regions.</p> <p>Structural changes were monitored by Transmission Electron Microscopy and ancillary techniques in order to provide a detailed characterisation of the fatigue state.</p>