Yoshikazu Higa

Modeling and estimation of deformation behavior of particle-reinforced metal–matrix composite

Abstract In order to estimate the characteristic feature of the deformation behavior of materials with a length scale, the strain gradient plasticity theories, corresponding variational principle and a finite element method are given. Then the finite element method is applied to the estimation of the mechanical characteristics of the particle reinforced metal–matrix composites modeled under plane strain conditions. The effects of the volume fraction, size and distribution pattern of the reinforcement particles on the macroscopic mechanical property of the composite are discussed. It has been clarified that the deformation resistance of the composite is substantially increased with decreasing particle size under a constant volume fraction of the reinforcement material. The main cause of the increase of the deformation resistance in the plastic range is the high strain gradient appearing in the matrix material, which increases with the reduction of the distance between particles.

Computational Modeling and Characterization of Materials with Periodic Microstructure using Asymptotic Homogenization Method

In order to clarify the micro- to macroscopic characteristic feature of two-phase single-crystalline materials, an asymptotic homogenization method has been developed for materials obeying the constitutive equation based on the dislocation-density-dependent crystal plasticity theory. We focus our attention on nickel-based superalloy that is well used in practice and in which fine and hard (gamma-prime phase: phase) precipitates are embedded in a soft (gamma phase: -γ-phase) matrix. Assuming that the cuboidal γ′-phase precipitates with a periodical distribution in the γ-phase matrix, a unit cell model consisting of two phases is established. Then, a series of computartional simulations adopting a constant -γ-precipitate size has been performed for the alloy with the different volume fractions of γ′-precipitates associated with the width of the γ-channel and the crystallographic orientations of the two phases. Results show that the effects of the γ′-precipitate volume fraction and the applied loading direction relative to the crystallographic orientation on the macroscopic deformation behavior are considerable as compared with the strain-gradient-independent model.

Multiscale Characterization of Deformation Behavior of Particulate-Reinforced Metal-Matrix Composite

In order to estimate the characteristic feature of deformation behavior of particulate-reinforced metal-matrix composites with a length scale, the strain gradient plasticity theories and a homogenization method are used. The effects of the volume fraction, size and distribution pattern of the reinforcement particles and of the direction of the applied force on the macroscopic mechanical properties of the composites are examined. It has been clarified that the deformation resistance of the composite increases with the decrease of the particle size under a constant volume fraction of the reinforcement and strongly depends on the distribution pattern of reinforcement particles and the direction of applied force. The main mechanism of the increase in deformation resistance in the plastic range is the high strain gradient which appears in the matrix material and increases with a reduction in the distance between the particles.

An Accuracy Estimate of Multiscale Analysis for Composite Materials Using Eigenstrain Fields and Its Application

In order to estimate the accuracy of multiscale analysis for materials with microstructures based on the eigenstrain fields formulated by Nemat-Nasser and co-workers, we performed the computational simulation employed the piecewise approximation method, so called Subdivisions Method that discretizies inclusion region into the sub-domains where the eignenstrains are taken as constant. Through the numerical evaluation of the overall properties and microscopic deformation behavior of elastic solids that contain periodically distributed hard inclusions in soft matrix, we found that the results significantly depend on the way of discretization of inclusion into subregion. The results of Subdivisions Method with subregions that have the same volume show the excellent agreement with those due to Homogenization Method, whereas, those with the different volume were very poor. Therefore, it has been concluded that Subdivisions Method with the same volume of subregion provide efficient tool for the estimation of the macroscopic mechanical properties of the materials with periodic microstructures. The Subdivisions Method with the same volume of subregion is applied to investigate the overall complex properties and microstrain of unidirectional/short-fiber reinforced composite materials and the effect of the location of reinforcements under a constant volume fraction on its macroscopic mechanical properties are clarified.

A Study of Brinell Hardness Test of Porous Materials.

The Finite Element Method is applied to the analysis of Brinell hardness test of porous materials. The numerical calculation is performed using four different plastic constitutive rules such as Gursons rule, Tvergaards modification of Gursons rule, Goya-Nagaki-Sowerbys rule and a stereology-based rule that is a modification of Goya-Nagaki-Sowerbys rule. For the investigation of the validity of the rules, the numerical results are compared with experimental data for the porous materials produced by Spark Plasma Sintering method which can product porous materials of higher porosity. From the comparison it is concluded that the numerical results obtained using Tvergaards modification of Gursons rule or the stereology-based modification can well predict the experimental results. However, the numerical results deviate from the experimental data for the porous material of higher porosity such as fo=0.3. This deviation is attributed to the fact that the shape of pores in the porous material of fo=0.3 are quite different from the sphere that is a fundamental assumption in developing constitutive rules.