Papers by Author: Mitsutoshi Kuroda

Abstract: In this paper, strain gradient plasticity theory is extended to include the corner-like effect that is inherent in crystal plasticity. The predictive feature of the extended theory is examined via finite element analysis of a constrained simple shear problem and a plane-strain tension problem involving plastic flow localization. Numerical issues with respect to finite element formulations are also discussed.

Abstract: In this study, the Bauschinger effect in ultrafine-grained pure aluminum rods (A1070) was investigated. The samples were produced by multipass equal-channel angular pressing (ECAP) with ‘route BC’, which is known to give nearly equiaxial-shaped crystal grains. Dumbbell-shaped specimens with a circular cross section were machined from the samples subjected to ECAP to carry out uniaxial tensile and compressive tests, which were followed by reversal of the loading direction at a prestrain of 1%. The influence of the grain size on the intensity of the Bauschinger effect was investigated. The Bauschinger effect is interpreted to be a manifestation of internal stresses produced near the grain boundaries by the accumulation of dislocations. On the basic of our experimental results, the roles of the grain boundaries, which are usually at least partially considered as barriers to dislocation motion, are reconsidered.

Abstract: In this study, a three-dimensional finite element formulation for polycrystalline plasticity model based on the homogenization method has been presented. The homogenization method is one of the useful procedures, which can evaluate the homogenized macroscopic material properties with a periodical microstructure, so-called a unit cell. The present study focuses on hexagonal metals such as titanium or magnesium. An assessment of flow stress by the presented method is conducted and it is clarified how the method can reproduce the behavior of hexagonal metal.

Abstract: In this study, effects of typical texture components observed in rolled aluminum alloy sheets (i.e. Copper, Brass, S, Cube and Goss texture components) on plastic flow localization are studied. The material response is described by a generalized Taylor-type polycrystal model, in which each grain is characterized in terms of an elastic-viscoplastic continuum slip constitutive relation. First, forming limits of thin sheet set by sheet necking are predicted using a Marciniak–Kuczynski (M–K-) type approach. It is shown that only the Cube texture component yields forming limits higher than that for a random texture in the biaxial stretch range. Next, three-dimensional shear band analyses are performed, using a three-dimensional version of M–K-type model, but the overall deformation mode is restricted to a plane strain state. From this simple model analysis, two important quantities regarding shear band formation are obtained: i.e. the critical strain at the onset of shear banding and the corresponding orientation of shear band. It is concluded that the Cube texture component is said to be a shear band free texture, while some texture components exhibit significantly low resistance to shear band formation. Finally, shear band developments in plane strain pure bending of sheet specimens with the typical textures are studied.