Papers by Author: Tetsuya Matsuda

Abstract: In this study, development of a decoupled multiscale analysis method for woven composites is conducted. To this end, an elastic-viscoplastic macroscopic constitutive model which is able to express strong anisotropy of composites is introduced, and the material parameters in the constitutive model are determined based on the results of triple-scale homogenization analysis. Moreover, the constitutive model is implemented in the finite element analysis code LS-DYNA. The developed method is applied to 3-point bending analysis of plain-woven carbon fiber-reinforced plastic (CFRP) composites with various types of laminates configurations. It is shown that the present method can analyze their different behavior depending on the laminate configuration with greatly reduced computational costs.

Abstract: In this study, the analysis method for thermomechanical properties of plain-woven composites is developed, and applied to thermoelastoviscoplastic analysis of plain-woven glass fiber-reinforced plastic (GFRP) composites. For this, a time-dependent constitutive equation depending on temperature for matrix materials is incorporated into the micro/meso/macro-scale thermo-elastic homogenization method for plain-woven composites developed by our research group. This method enables us to analyze thermoelastoviscoplastic properties in not only fiber bundles but also fibers and matrix materials in fiber bundles, as well as macroscopic thermal properties. This method is then applied to the thermal expansion analysis of a plain-woven GFRP composite subjected to a macroscopic temperature change from 25°C to 80°C before it is cooled to 25°C. Comparing the analysis results with experimental data, we validate the present method. It is also shown that the present method can evaluate themal residual stress and strain in the composite.

Abstract: In this study, a through-the-thickness negative Poisson's ratio of an angle-ply carbon fiber-reinforced plastic (CFRP) laminate is experimentally investigated using a 3D digital scanning method. For this, an image-based measurement method using a 3D digital scanner is developed to obtain the thickness change of CFRP laminates. The thickness change is used to calculate the through-the-thickness Poisson's ratio of CFRP laminates. Then, a tensile test of a [±θ°] angle-ply CFRP laminate is performed, and the through-the-thickness Poisson's ratio is measured based on the developed method. The results obtained suggest that the through-the-thickness Poisson's ratio exhibits negative values which become increasingly negative as (visco)plastic deformation progresses in the laminate, as demonstrated in our previous analysis.

Abstract: In this study, a two-scale thermoelastoviscoplastic analysis method for carbon fiber-reinforced plastic (CFRP) laminates is proposed based on a homogenization theory for time-dependent composites. For this, macroscopic and microscopic boundary value problems for CFRP laminates are derived to discuss the relation between the two problems. Using the relation, a two-scale thermoelastoviscoplastic analysis method is constructed, and then applied to the analysis of thermal behavior of an unsymmetric cross-ply carbon fiber/epoxy laminate. The laminate is subjected to a macroscopic temperature change from 180°C to 20°C. It is shown that quite high residual stress and strain occur both macroscopically and microscopically in the laminate, resulting in large macroscopic warpage of the laminate.

Abstract: In this study, thermal properties of plain-woven laminates are analyzed micro-, meso-and macroscopically based on a multiscale approach. For this, the effects of thermal expansion of constituents are incorporated into the micro/meso/macro homogenization method for plain-woven laminates developed by our research group. This method enables us to analyze thermal properties of not only fiber bundles in laminates but also fibers and matrix materials in fiber bundles, in addition to their macroscopic thermal properties. The present method is then applied to the thermal property analysis of plain-woven carbon fiber/epoxy laminates subjected to a macroscopic temperature change from 180°C to 20°C. Two types of carbon fibers, i.e. HTA and P75, are considered in the analysis. It is shown that quite high thermal residual stress can occur in fiber bundles, fibers and a matrix. It is also shown that the present method can predict the change of thermal properties of the laminates depending on the difference of fibers.

Abstract: The elasto-viscoplastic behavior of slanting-weft woven laminates, the fiber bundles of which are not crossed at a right angle, is investigated both macroscopically and microscopically. For this, an analysis model for the [±θ] slanting-weft woven laminate with a cross angle ±θ and its diamond-shaped unit cell are considered. Then, a basic cell, which is quarter of the unit cell, is defined as an analysis domain by considering the point-symmetry of the internal structure. For the basic cell, the homogenization theory for nonlinear time-dependent composites with point-symmetric internal structures is applied. Using the present method, the elasto-viscoplastic analysis of the [±θ] slanting-weft woven laminates subjected to an in-plane uniaxial tensile load is performed. From the analysis results, the macroscopic elasto-viscoplastic behavior and the microscopic stress and strain distributions of the laminates are investigated.

Abstract: Effects of laminate misalignment on the thermoelastoviscoplastic properties of ultrafine plate-fin structures are investigated using a homogenization theory for thermoelastoviscoplasticity. For this, a homogenization theory for time-dependent materials is combined with a homogenization theory for thermoelasticity. Moreover, the substructure method is introduced into the theory to deal with the random laminate misalignment in ultrafine plate-fin structures. The present method is then applied to the analysis of thermoelastoviscoplastic behavior of ultrafine plate-fin structures made of a Ni-based alloy subjected to a macroscopic temperature increment from 20 to 200. The number of fin layers in a unit cell is five kinds, i.e. N = 10, 20, 30, 40 and 50, for each of which, twenty patterns of random laminate misalignment are considered. In addition, five cases of periodic laminate misalignment are also considered for comparison. The results reveal the effects of the laminate misalignment on the macroscopic and microscopic thermoelastoviscoplastic properties of ultrafine plate-fin structures.

Abstract: A fully-modeled unit cell analysis is performed to investigate the macroscopic and microscopic elastic-viscoplastic behaviors of a quasi-isotropic carbon fiber-reinforced plastic (CFRP) laminate. To this end, a quasi-isotropic CFRP laminate and its microstructure composed of carbon fibers and a matrix material are considered three-dimensionally. Then, a hexagonal prism-shaped unit cell fully modeled with fibers and a matrix including interlaminar areas is defined. For this quasi-isotropic laminate, a homogenization theory for nonlinear time-dependent composites with point-symmetric internal structures is applied, enabling us to analyze both the macroscopic and microscopic elastic-viscoplastic behaviors of the laminate. The substructure method is introduced into the theory to reduce computational costs. The present method is then applied to the elastic-viscoplastic analysis of a quasi-isotropic carbon fiber/epoxy laminate subjected to an in-plane uniaxial tensile load, to investigate the macroscopic elastic-viscoplastic behavior of the laminate and the microscopic stress and strain distributions in them.

Abstract: In this study, macro/meso/micro elastic-viscoplastic analysis of plain-woven laminates is conducted based on a homogenization theory for nonlinear time-dependent composites. For this, a plain-woven laminate is modeled with respect to three scales by considering the laminate as a macrostructure, fiber bundles (yarns) and a matrix in the laminate as a mesostructure, and fibers and a matrix in the yarns as a microstructure. Then, an elastic-viscoplastic constitutive equation of the laminate is derived by dually applying the homogenization theory for nonlinear time-dependent composites to not only the meso/micro but also the macro/meso scales. Using the present method, the elastic-viscoplastic analysis of a plain-woven glass fiber/epoxy laminate subjected to on-and off-axis loading is performed. It is shown that the present method successfully takes into account the effects of viscoplasticity of the epoxy in yarns on the elastic-viscoplastic behavior of the plain-woven GFRP laminate. It is also shown that the results of analysis are in good agreement with experimental data.

Abstract: In this study, the elastic-viscoplastic properties of aluminum honeycomb sandwich panels are investigated using a homogenization theory for free edge analysis. For this, the mathematical homogenization theory is reconstructed for elastic-viscoplastic analysis of honeycomb sandwich panels by introducing a traction free boundary condition. Moreover, the domain of analysis is reduced to a quarter using point-symmetry of internal structures of honeycomb sandwich panels. The present method is then applied to the analysis of macroscopic elastic-viscoplastic behavior and microscopic stress distribution of an aluminum honeycomb sandwich panel subjected to in-plane uniaxial compression. It is shown that the stress concentration arises at face/core interfaces, especially at intersections of core walls.