Effet de l'espacement interlamellaire sur le comportement sous chargements monotone et cyclique de l'acier perlitique C70.

Abstract : The effect of interlamellar spacing on the monotonic and cyclic behavior of C70 pearltic steel was investigated. Tensile tests under scanning electron microscope and under X-ray diffraction coupled with self-consistent model have been used. Tests have been carried out on two microstructures with different interlamellar spacing. It has been demonstrated that pearlite yielding is controlled by ferrite critical shear stress), which depend on the interlamellar spacing. The pearlite deforms inhomogeneously under tensile loading by localized shearing in intense shear bands. In the large shear bands, parallel cementite plate offsets before fracture and contributes to the occurrence of localized damage. The residual stress in ferrite is higher for the coarse pearlite. Giga-cycle fatigue tests were performed to identify the effect of interlamellar spacing on the fatigue behavior; tests were performed at a frequency of 20 KHz. The difference of the fatigue strength between 106 and 109 cycles is about 30 MPa for coarse pearlite and 50 MPa for fine pearlite. The effect of interlamellar spacing on the mega-cycle and giga-cycle fatigue limit appears not significant compared to the mechanical characteristics. Giga-cycle fatigue limit obtained includes the beneficial effect of stabilized residual stress. It also includes the effect of hardening induced by machining and cyclic hardening. However, any significant effect of interlamellar spacing on the C70 fatigue limits has been shown. SEM examinations shows that failures initiated on surface for the mega-cycle regime and on different sites for the giga-cycle regime. The experimental results can be interpreted based on the effects of stabilized surface properties and microstructure. The use of a fatigue Goodman criterion would identify qualitatively the contribution of different factors, cited above, in the fatigue life.
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Houda Yahiaoui. Effet de l'espacement interlamellaire sur le comportement sous chargements monotone et cyclique de l'acier perlitique C70.. Mécanique [physics.med-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2013. Français. ⟨NNT : 2013ENAM0025⟩. ⟨pastel-01062071⟩

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