618 二相多結晶合金のバウシンガー挙動に及ぼす不均質性の影響に関する場の理論的研究(OS06.材料の組織・強度に関するマルチスケールアナリシス(5))

Abstract

Abstract The effect of trans-granular inhomogeneity on Bauschinger behavior, i.e., transient and permanent softening including early re-yielding is systematically investigated for dual-phase polycrystal models by using crystal plasticity-based simulation. Three hard phase (HP) distributions with volume fraction of 50% are taken as examples, which exhibit distinct Bauschinger behaviors corresponding to different duality distribution of fluctuating stress and strain fields. Random and lamellar-like HP models exhibit larger transient and small permanent softening, whereas block-like HP model shows the opposite trends. Detailed correspondences between the duality and Bauschinger are extensively examined. Key words: Crystal Plasticity, Field Theory, Bauschinger effect, Finite Element Method, Dual Phase Steels, INTRODUCTION High strength steels (HSSs) used for automobile bodies yield very large spring back during stamping processes. The prediction of the springback behavior especially for the HSSs is, however, generally very difficult because these steels have complex microstructures [1-3], and no practically-satisfactory physics-based model has been developed to date [3] in spite of the strong and urgent needs from industry. Furthermore, they subject to complex loading incl uding load reversal e.g. bending and anti-bending at the bead portions [2]. Therefore, the Bauschinger behavior plays crucial roles in the spring back evaluation. Regarding the Bauschinger effect, while operating mutually with the plural scales, the inequality which advances Because it has the beginning in the quality st ress strain field, double layer like the high intensity steel sheet High accuracy estimate of the same quality in the practical polycrystal metallic materials which possess microstructure The high-level model which is based on multiple scale viewpoint becomes necessary in measuring. Namely, when catching plastic phenomenon, the principal 3 scales after specifying, the place Fluctuation of the heterogeneous place with each scale which is based on theory from viewpoint of the correlation. Bauschinger behavior is roughly organized into two types of softening, i.e. they are transient softening and permanent softening, where the transient softening includes early re-yielding [2]. These Bauschinger behaviors are known to be sensitive to inhomogeneity of deformation at multiple scale levels. In this study, we intend to clarify th e effect of inhomogeneity in the transgranular scale on the Bauschinger behavior for polycrystal, which crucially affect the springback characteristics during the stamping processes, from a novel viewpoints based on the field theo ry of plasticity [4-6]. For this purpose, a crystal plasticity-based finite element simulation is carried out on dual phase polycrystalline models with three hard phase distributions. Duality fluctuations between hydrostatic stress and deviatoric strain fields are extensively investigated based on the field theory [5,6] in order to examine the relationship between the