Kazuaki Nishiyabu

The formulation of homogenization method applied to large deformation problem for composite materials

In order to analyze the mechanical behaviors of composite materials under large deformation, the formulation of the homogenization method is described. In this formulation, assuming that the microstructures in a local region of the global structure are deformed uniformly and that consequently the microscopic periodicity remains in the local region under large deformation, the microscopic deformation is precisely defined by the perturbed displacement and product of macroscopic displacement gradient and microscopic coordinates. Finally, microscopic and macroscopic equations are obtained. The above mentioned assumption of the periodicity of microstructures is experimentally validated. The computer program is also developed according to this formulation, and the large deformation is analyzed for the unidirectional fiber reinforced composite material and the knitted fabric composite material.

Microstructure-based deep-drawing simulation of knitted fabric reinforced thermoplastics by homogenization theory

Abstract Process simulation of fiber reinforced composite materials is an important research theme for the development of low-cost and advanced functional composite materials. This paper aims at the simulation of deep-drawing process of knitted fiber reinforced thermoplastics and its verification. The feature of the simulation is that the large deformation of the knitted microstructures can be traced everywhere in the deep-drawn product. The homogenization theory is applied to analyze the micro–macro coupled behaviors of the knitted fabric composite material. By employing a simplified nonlinear computational algorithm, the deep-drawing simulation was carried out on a personal computer. The predicted largely deformed microstructures were compared with the experimental results. The numerical results and experimental ones agreed quite well. This deep-drawing simulation requires us to prepare only the mechanical properties of the constituents, while it provides us all the necessary quantities such as the deformation, strain, stress and stiffness from both microscopic and macroscopic standpoints.

Strain concentrations in woven fabric composites with holes

Abstract A strain mapping technique, namely digital photogrammetry, was used to investigate the tensile strain field of woven fabric composites in the presence of stress concentrations caused by geometrical defects consisting of circular or elliptical holes. Plain woven fabrics were used. The strain mapping technique clearly revealed the strain concentrations near the singularity. The strain concentrations are influenced by the tensile loading direction and the hole dimension relative to the size of the unit cell of the plain woven fabrics. A preliminary comparison of stresses approximately calculated from the strain field and theoretical stresses calculated from existing models such as Lekhnitskii’s model is also presented.

Micro Metal Injection Molding Using Hybrid Micro/Nano Powders

This study aims to investigate the effects of hybrid micro/nano powders in a micro metal injection molding (μ-MIM) process. A novel type of mixing-injection molding machine was used to produce tiny specimens (<1mm in size) with high trial efficiency using a small amount of feedstock (<0.05cm3 in volume). Small dumbbell specimens were produced using various feedstocks prepared by changing binder content and fraction of nano-scale Cu powder (130nm in particle size). The effects of adding the fraction of nano-scale Cu powder on the melt viscosity of the feedstock, microstructure, density and tensile strength of sintered parts were discussed.

Porous Graded Materials by Stacked Metal Powder Hot-Press Moulding

The production method for metal components with micro sized porous structure has been developed by applying “powder space holder method” to metal powder injection molding process. In this study, a co-sintering process was utilized to make a plate of sintered metal with micro porous graded structure. The green compact sheets with various contents of space hold particles were prepared by hot press molding for simplification. The five layers of metal with symmetric structure, which the skin layer was formed with high density metal and the core was formed with open or closed porous structure, or with inverse symmetry, was obtained by changing stacking sequence in co-sintering process. Mechanical properties of the materials with plain homogeneous porous structure and porous graded structure were compared. The usefulness of proposed method for producing the metal components with micro porous graded structure and the effective of graded structure to compensate the deficiencies on the mechanical property of porous metals was shown.

Innovations in Micro Metal Injection Molding Process by Lost Form Technology

The production method of micro sacrificial plastic mold insert metal injection molding, namely μ-SPiMIM process has been proposed to solve specific problems involving the miniaturization of MIM. The sacrificial plastic mold (SP-mold) with fine structures was prepared by injection-molding polymethylmethacrylate (PMMA) into Ni-electroform, which is a typical LIGA (Lithographie-Galvanoformung-Abformung) process. Stainless steel 316L feedstock was injectionmolded into the SP-mold which had micro structures with multi-pillars. The green compact was demolded as one component with the SP-mold, which was decomposed along with binder constituent of feedstock in debinding process. This study focused on the effects of metal particle size and processing conditions on the shrinkage, transcription and surface roughness of sintered parts, which were evaluated by SEM (Scanning Electron Microscope) observation.

Net-Shape Manufacturing of Micro Porous Metal Components by Powder Injection Molding

A novel production method for porous metal components has been developed by applying powder space holder (PSH) method to metal powder injection molding (MIM) process. The PSH-MIM method has an industrial competitive advantage that is capable of net-shape manufacturing the micro-sized porous metal products with complicated shapes and controlled porosity and pore size. In this study, the small impeller with homogeneous micro-porous structure was manufactured by the PSH-MIM method using porous compounds composed of fine stainless steel 316L powder and polymethylmethacrylate (PMMA) particle. The effects of combinations in size and fraction of PMMA particle on dimensional tolerance and variation of sintered porous specimens were investigated. It was concluded that the PSH-MIM method could manufacture commercially micro-porous metal components with high dimensional accuracy.

Micro Metal Powder Injection Molding

Powder injection molding (PIM), which encompasses metal powder injection molding (MIM) and ceramic powder injection molding (CIM) is a net-shape process for the manufacturing of high volume and high precision components for use in a variety of industries. The micro-miniaturization of dimension and structures in MIM is facing with various technical problems, such as incomplete filling to narrow cavity, failure in demolding of fragile green compacts, and deformation in debinding and sintering process. Therefore micro MIM (μ-MIM) process is a more sophisticated process for tiny metal components and micro structured parts. This chapter introduces a general flow of MIM process, the material properties of the feedstock and focuses on the unique phenomena in the micro injection molding and the filling behaviour. A flow simulation of micro gear and micro dumbbell tensile specimen will be carried out and the flow pattern by short shot test and internal pressure measured will be compared to the simulation results. The production method of micro sacrificial plastic mold insert MIM (μ-SPiMIM) process has been proposed to solve drastically the specific problems involving the miniaturization of MIM parts. The sacrificial plastic mold (SP-mold) is prepared by injection-molding polymethylmethacrylate (PMMA) polymer into Ni-electroform. Micro-sized stainless steel 316L powder feedstock is injectionmolded into the SP-mold which consists of micro multi-pillar structures. The effects of metal particle size and processing conditions on the quality of molded and sintered parts are evaluated. For the higher quality of μ-SPiMIM process, the feedstock composed of nanosized Cu powder and oxymethylene-based binder is adequately prepared and molded into PMMA films with fine line-scan structures which are prepared by nano-imprint lithography (NIL) technique. From the evaluation results on the effects of particle size of metal powder and processing conditions toward the high precision of sintered parts, it is concluded that the μ-SPiMIM process has a great potential to produce precisely the complex metallic parts with fine micro-structures.

Fabrication and Mechanical Properties of Functionally Graded Micro Porous Metals by Mim-Base Powder Space Holder Method

This study describes the manufacturing method based on metal powder injection moulding for micro porous metal components with high functionally graded sandwich structure. The effectiveness of sandwich structure produced by co-sintering and co-injection moulding processes to compensate the deficiencies on the mechanical property of porous structures, was investigated.

Small is better if testing MIM nano theories

The jury would still appear to be out considering the benefits of nanotechnology in metal injection moulding. Japanese researchers built their own tiny table-top direct mixing injection moulding machine to put theory to the test…