Noriyoshi Kumazawa

Homogenization method for heterogeneous material based on boundary element method

Abstract In this paper, formulations for homogenization method based on the boundary element method, for heterogeneous elastic materials having periodic microstructure, are presented. The formulations are developed using a novel use of the method of weighted residuals. Both the trial and test functions are expressed by asymptotic expansions with respect to the size e of the unit cell. Two types of boundary element formulations for the analysis of unit cell, are proposed; single-region boundary element method with volume integrals and multi-region boundary element method. Convenient formulae to compute effective (homogenized) elastic constants, are presented.

Numerical analysis on near net shape forming of Al-Al3Ni functionally graded material

Abstract The results of numerical studies on the near-net shape forming of Al–Al3Ni functionally graded material (FGM) are presented and are compared with the experiments. FGM billets at an elevated temperature of semi-solid condition are set in a container and are subject to backward extruding, and FGM cups are obtained. Due to the composition gradient of FGM the effective viscosity of semi-melt FGM billet varies spatially. The flow/deformation of semi-melt FGM billet is strongly influenced by the spatial variation of effective viscosity. Some characteristic behaviors of flow/deformation of FGM during the semi-solid process are presented and discussed.

Novel Concept to Detect an Optimum Thixoforming Condition of Al-Al3Ni Functionally Graded Material by Wavelet Analysis for Online Operation

A novel technique to characterize the transition phenomenon from solid to melt of Al-Al3Ni functionally graded material (FGM) through a wavelet analysis for the development of a thixoforming system is investigated. Identification of an optimum semi-solid condition for thixoforming is necessary not only for the construction of a system but also the fabrication of a near-net-shape product with fine microstructure. An online wavelet analysis system using Haar’s wavelet function, which is applied for its simplicity compared with Daubechies’ wavelet function, is developed to find the optimum operating condition. A thixoforming system, which is constructed adapting a threshold value as an index, monitors successfully a discontinuity of deformation of Al-Al3Ni FGM with the temperature rise. Thus, the timing of an operation is not at pre-fixed temperature but at the time when the index related to a wavelet function is satisfied. The concept is confirmed to be suitable from the micro-structural observation of the Al-Al3Ni FGM product, because the product under the optimum condition is found to have refined Al3Ni grains, which change from coarse grains and are expected to improve the mechanical properties.

705 Analysis of Deformation Behavior of Semi-Solid Hypereutectic Al-Si Alloy Compressed in the Drop-Forge Viscometer

The aim of this study is to investigate the rheological behavior for a semi-solid forming of Al−25 mass % Si alloy, i.e., hypereutectic Al-Si alloy, using a self-made parallel-plate drop-forge viscometer. Drop-forge experiments show individually the features that the viscosity decreased in the early increasing shear rate stage and subsequently the viscosity turned to increase as the shear rate decreased. Thus, the viscosity takes a minimum around the maximum shear rate. The summarized behavior between the viscosity,  [Pa・s], and the shear rate,  g [s], can be described by a power-law model of = 1.78×10  g . The decrease in viscosity accompanied with the increase in the shear rate depends on both rises in the temperature and the applied force, not the duration of forging. The convex shape curve is observed between the effective duration and the viscosity and the effective duration reaches a maximum at around =30 kPa・s where  g =70 s. The origin of the profile is due to the lost of ability to transform the kinetic energy to distortion energy, which is caused by a decrease of deformation resistance accompanied with a decrease of viscosity. Then the viscosity =30 kPa・s, which corresponds to the transition point from plastic forming to casting, seems to be the optimum condition for semi-solid forming.

Analyses of Progressive Damage and Fracture of Particulate Composite Materials Using s-FEM Technique

In this paper, the s-fem (s-version FEM; an element overlay technique [1,2,3,4]) is applied to the damage analyses of particulate composite materials (Fig. 1 (a)). We conduct a series of unit cell analyses in which we assume many (≈40) distributed reinforcing particles. We assume two kinds of damage modes in our analyses. One is due to microvoid formation in matrix material that is accounted for by a continuum damage model [5]. The damage constitutive model is extended so that the modes of damage can be split to dilatational and deviatoric parts. Another damage mode is “dewetting” between the reinforcing particles and matrix material. The cohesive zone model [6,7] is adopted to appropriately model the separation between particles and matrix material.

Analysis for Particulate Composite Materials undergoing Damage and Stress Induced Phase Transformation using the Boundary Element Method

In this paper, formulations for the analysis of particulate composite materials whose particles undergo particle fracture/interface debonding or stress induced phase transformation. The formulations are developed based on a boundary element based homogenization technique where the influences of differences in elastic properties between matrix and particles and transformation strains are accounted for by using analytical expressions. Macroscopic stresses are computed based on the homogenization method. Hundreds of particles which undergo particle fracture/interface debonding or stress induced phase transformation are placed in a unit cell for the homogenization analysis. Thus, quasi-smooth macroscopic stress-strain curves can be generated based on particle fracture/interface debonding or phase transformation criterion for each particle. 650, 125, 35 and 3 particle modeles are analyzed in this paper.

Application of optimal regulator with time delay to temperature control for thixoforming system

Abstract An optimal feedback law minimizing an objective function including memories of states is proposed. It was not clear how to select the design parameters using the control law. In this paper, we describe a stabilized parameter domain of the proposed optimal regulator and apply the pair of parameters to the controller, which is adapted to a thixoforming system in which temperature is regulated. The control law is confirmed to have performed well from the numerical and experimental results.