Papers by Keyword: Polycrystalline Metal

Abstract: In the previous papers, the author discussed the role of r-value (anisotropic parameter in plasticity) on the surface roughening after plastic deformation. In the present paper, discussion is made on the effects of mutual constraint of deformation between neighboring grains at the grain boundary on the surface roughening. A characteristic parameter called constraint ratio is introduced to express the degree of the mutual restriction between grains. The well-known Coffin-Manson relation in low cycle fatigue is deduced considering to the surface roughening after cyclic deformation.

Abstract: The r-value is defined as the ratio of the width strain to the thickness strain under uniaxial tensile loading. The r-value can be defined for each grain in polycrystalline metal during plastic deformation. It was pointed out that r-value of a grain affects the surface roughening of polycrystalline metal, and hence also affects the formability of thin sheet metal. On the other hand, it was shown that by using a rate-type constitutive relation for crystal slips the effect of the number of active slip systems on the yield curves is clarified. In the present paper, the relation between r-value of a grain and its operating slip systems in polycrystalline metals is studied.

Abstract: Power spinning is one of the effective ways to refine grains of material and improve its mechanical properties. To explore the severe plastic deformation mechanism of power spinning for polycrystalline metal, the construction of mesoscopic plastic constitutive model and geometrical model was introduced in detail. A 3D representative volume element (RVE) of microstructure for polycrystalline materials was developed based on the finite element software ABAQUS by Matlab and Python script, and the parametric finite element gridding was realized with the LaGriT tool, which lays a solid foundation for the finite element simulation and prediction of microstructure evolution for power spinning of polycrystalline metal.

Abstract: To understand the free surface roughening phenomena of polycrystalline metals, the surface roughening behaviors of three kinds of metal sheets were investigated under uniaxial tension. The materials used were AZ31 magnesium alloy, SPFC 590Y steel, and A5052-O aluminum alloy. In the in-situ observation of surface roughening for AZ31 magnesium alloy, it seemed that the surface of each grain roughened independently and the roughness increases with increasing plastic strain. In contrast to A5052-O and SPFC, the anisotropy of free surface roughening was observed for AZ31 magnesium alloy. Compared with planar anisotropy , the microscopic anisotropy of surface roughening is not related to . In AZ31 magnesium alloy, the anisotropy of surface roughening arises and, instead of the r-value, another parameter is needed to evaluate the anisotropy of free surface roughening.

Abstract: Biaxial compression tests with an abrupt strain path change have been performed on polycrystalline aluminum to investigate the plastic deformation behavior under complex strain histories. Attentions are paid especially to the rapid change in the normal stresses due to the abrupt strain path change. The influences of the prestrain amplitude and the angular relation of sequential strain paths on the stress changes were also studied. The results showed that the transient increase of the normal stresses related to the latent hardening phenomenon with strain path change as well as the plastic anisotropy increase with the pre-straining amplitude. The transient increase in the stress was also affected by the strain histories in the sequential compression tests with the strain path change. The transient stress increment became large to the maximum then decreases with the angle between the sequential paths.

Abstract: A new model describing the reaction stresses during plastic deformation of metals is proposed in which the reaction stresses among the grains and their accumulation are calculated. The model could overcome the shortages of the Sachs and Taylor deformation model. According to the model, the plastic strain tensor induced by activation of slip systems will produce certain elastic reaction stress in the surrounding matrix, which influences the choice of further activation of slip systems as well as the orientation evolution. The model gives more attention to both of the stress and strain compatibility among the grains. The simulation on the tensile deformation of pure copper indicates that the model could exhibit the main characteristics of the real deformation process.