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The strain space multiple mechanism model idealizes the behavior of granular materials based on a multitude of virtual simple shear mechanisms oriented in arbitrary directions. These mechanisms idealize the micromechanical structure of granular materials with induced anisotropy and form a second-order fabric tensor, which relates macroscopic strain to macroscopic stress and has been updated to consider the effect of inherent anisotropy. This paper investigates the inherent anisotropy's effect on the evolution of induced fabric under pure shear loading. Comparison with Discrete Element Method (DEM) simulation demonstrates that the strain space multiple mechanism model accounting for inherent anisotropy has the potential to capture the essential features in the evolution of an induced fabric in granular materials subject to pure shear.

In this study, we perform the basic verification of an extended Flory-Rehner (F-R) model using experimental data of polyacrylamide hydrogels. The equilibrium free swelling and subsequent uniaxial tensile tests are experimentally performed to determine two scaling exponents characterizing the extended F-R free energy function for polymeric gels. To show the ability of the two scaling exponents, the Ogden model is compared as the different strain energy in the F-R model....

In this study, we perform finite element implementation of a free energy function extended by introducing two scaling exponents into the Flory-Rehner model for swollen elastomers. This extended model is implemented into the finite element package Abaqus using the user-defined material subroutine UHYPER. To verify this implementation, the stress-stretch responses of elastomers at equilibrium swelling under uniaxial tension are simulated and compared with analytical predictions....

Porous ceramics have nonlinear stress-strain behavior and are expected to have damage tolerance capability. To assess the nonlinear behavior, we have proposed distributed-micro-crack model. In this paper, some assessment results with the distributed-micro-crack model for porous ceramics are presented. The effects of R-curve behavior and stress concentration are included in the assessment. Constitutive equation of distributed-micro-crack model has been expanded from uniaxial stress model to multiaxial stress model to consider the stress concentration. It was found that our proposed model can simulate the nonlinear stress-strain relationship of porous ceramics for various loading condition such as 3-point bending, 4-point bending with smooth specimen and 4-point bending with notched specimen etc. These simulations also show that 3-point bending test is suitable for assessing nonlinear stress-strain behavior than 4-point bending because 3-point bending can localize the nonlinear stress-strain behavior region which is easily measured by strain gage.

In order to investigate the effect of loading frequency on stress-strain-temperature relationship in pseudoelastic behavior of Shape Memory Alloys (SMA), tensile tests of TiNi-SMA wire at loading frequencies ranging from 0.001 Hz to 1 Hz were performed, and the stress, strain and temperature of wire were measured simultaneously. Using our proposed thermo-mechanical analytical model of SMA, those pseudoelastic behaviors were simulated numerically as well. Results showed that the loading frequency strongly affects temperature change of the wire and the stress-strain hysteresis loop. The analytical model could predict the time history of stress-strain-temperature relationship with accuracy, and thus the validity of the model has been confirmed. Moreover, by examining the variation of each term of the heat balance equation, the thermo-mechanical mechanism of the pseudoelastic behaviors was also clarified.

In the first part of this paper, a series of systematic experiments of 5083 AI alloy are carried out at 833 K to elucidate the characteristic features of superplastic deformation under multiaxial loading conditions. Proportional deformation tests at constant strain-rates show that the initial yield stresses obey the Prager-Drucker criterion. It is also shown that under constant strain-rate tests the material hardens under tension, while it softens under compression. Significant strain-rate dependence of the flow stresses is elucidated for tension, compression and torsion loadings. In the second part of the paper, the constitutive model of superplasticity formulated in the previous paper is improved to obtain better description of the drop of the flow stress due to cavity growth under tension loading. For this purpose, the concept of effective stress and the strain equivalence principle of continuum damage mechanics are introduced into the model, and the relevant evolution equations are modified. Comparison of the results of the proposed model with those of the corresponding experiments shows that the proposed model gives better predictions than previously proposed by the authors.

The purpose of this paper is to propose a new constitutive model for concrete. As the load-carrying mechanism of concrete, a number of micro-crack model are assumed to be distributed with various orientations, sizes and densities in the concrete, and effect of crack growth at the microscopic level is modeled utilizing theories of Linear Elastic Fracture Mechanics (LEFM). Some numerical computations for fracture process of concrete prisms under uniaxial and biaxial tension or compression load are well simulated, using Finite Element Method (FEM) with the proposed constitutive model. The calculation results agree with the experimental ones.

The paper describes the constitutive model for a particle dispersed composite material in elastic regime. Two models, which are EMT model and SCC model, are proposed. The former is based on the Eshelby's equivalent inclusion concept and the Mori-Tanaka's mean field theory, as published other models often practice. EMT assumes that the compliance surrounding the particle is the same as that in the matrix, whereas the SCC does in the averaged composite. In SCC, the final formula of the constitutive law is obtained in a self-consistent form, where the solution is obtained in an iterative fashion. The accuracy of those were checked with a meso-mechanics analysis by FEM performed on a uniaxial tension of an infinite composite domain. The accuracy of the models by EMT and other existing models depends on the volume fraction of the inclusion and also on the rigidity ratio of the two phases, giving satisfactory results only up to about thirty percent of volume fraction. On the other hand, SCC model returns quite a good accurcy over the entire ranges of the volume fraction and the rigidity ratio that includes void inclusions and rigid inclusions as extremes. The paper also discusses the significance of microgeometric effects on the global material performance.

研究期間:平成9-10年度 ; 研究種目:基盤研究C2 ; 課題番号: 09650105, 原著には既発表論文の別刷を含む。