In the paper, the mechanical properties and its viscoelastic behavior of microcellular plastics ware investigated with particular emphasis on the role of cell size. A polyethylene terephtalate resin (CPET) modified with a polyolefin nucleating agent was selected as the specimens. In order to investigate the role of cell size, microcellular CPET samples were produced having constant cell density of 10⁹ cells per cubic centimeter, and a varying cell size in the range of 3 to 10μm.
The storage modulus time-temperature dependence of microcellular plastics was measured by using a viscoelastic analyzer and the tensile strength was investigated by use of a hydraulic tensile test machnine. It was found that compared with the original polymer, the storage modulus of microcellular polymers appears to relieve at a slower rate at elevated temperatures. The tensile strength of microcellular CPET with cell size of 3.5μm equals or more that of the original material.

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Rubber modified plastics have been studied by many researchers, and the relationship between mechanical properties and microscopic structures has been investigated by use of numerical analysis. In most numerical analyses, a linear-elastic constitutive law was applied for rubber because of its much lower elastic modulus.
We have tried to analyze a plastic/rubber blend system by use of non-linear FEM (MARC K-4). In this study, we applied elasto-plastic and Mooney-Rivlin constitutive laws to plastic and rubber regions respectively. Interesting results were obtained from numerical results.
The results are summarized as follows;
(1) After the test piece was tensioned at 25% strain, it unloaded. Unloading behaviors of plastic/rubber blend systems were qualitatively demonstrated by combinational use of elasto-plastic and Mooney-Rivlin constitutive laws.
(2) We proposed to adopt a 5-parameter Mooney-Rivlin constitutive law where the rubber region which is subjected to large deformation.

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The reinforcing effects of shirasu balloons and glass microballoons in solid polymers are investigated with respect to volume fraction of filled particles on the Young's moduli and yield stress of the reinforced composiites. The effect of polyester resin coated on the surface of the shirasu balloons is also discussed in order to find a method to produce composites with high toughness and low density. The specimens were made from low density polyethylene as the matrix, glass microballoons and shirasu balloons as hollow particle fillers and polyester as the coating material.

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The Dispersion behavior of a heterogeneous structure, which consists of an aggregate or agglomerate of particles and voids at the polymer-particle interface, has been studied by acoustic microscopy for polypropylene (PP) filled with surface modified calcium carbonate (CaCO₃). In order to improve the affinity at the interface between PP and CaCO₃, mono alkyl dihydrogen phosphate of different carbon number (MAP_n) were tested as modiflers for CaCO₃, PP and CaCO₃ were mixed on a two-roll mill and the films were prepared by compressing the mixed compound.
Using ultrasonic images, a binarization method was carried out to obtain the area fraction of the heterogeneous tructure in PP/CaCO₃ composites. Next, the relationships between the area fraction of the heterogeneous structure and carbon number of MAP_n density, void at polymer-particle interface accompanying the elongation, mechanical propreties (tensile elongation at break, modulus, yield stress) of PP/CaCO₃ composites have been investigated. The area fraction of heterogeneous structure largely decreased with the modification of CaCO₃ surface. The dependence of heterogeneous structure on the value of MAP_n was determined in this work. Although the tensile elongation at break and void at polymer-particle interface depended on the heterogeneous structure, the density, yield stress and the modulus of PP/CaCO₃ composites were nearly constant, irrespective of the area fraction of heterogeneous structure.

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The mechanical properties of particle-filled-polymer composites depend on the shape and size of particles and the state of dispersion. In this study, we examined the effect of surface treatment of the particles on the fracture behavior of CaCO₃ filled polypropylene (PP) in terms of the J-integral based on non linear fracture mechanics. While neat PP showed semi-brittle fractare, particle filled PP fractured in a ductile manner showing the initiation of small cavitation around the particles. The cavitation enhanced plastic deformation of the matrix material between their cavities. PP filled with untreated particles showed reduced toughness. The development of the damage zone during ductile crack growth for untreated particle-filled-specimens showed a small difference from that of specimens filled with stearic acid treated particles. The large voids, which initiated from several agglomerates of the particles within the damage zone of untreated particle filled PP, connected easily with each other at a lower loading and a lower deformation energy level.

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Fiber reinforced composites using the waste cord of synthetic fibers as the matrix material were molded by injection molding. The waste cord of polyester and nylon 6 fabrics having thermoplastic characteristics was fed into the molding machine directly together with the reinforcements in order to simplify the molding process. Glass and carbon fibers were used as the reinforcements and the reinforcement content was varied for the experiments.
The tensile strength and modulus of the composites were much larger than those for the matrix material, and increased with increasing reinforcement content. It is concluded that the molding system devised here is effective for the recycle of the waste cord of synthetic fibers.

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A unique method for the production of well mixed reinforced fiber/thermoplastic fiber mats for compression molding or stampable sheet molding was developed. In this method, bundles of continuous or discontinuous fibers are supplied to the apparatus, which is called “fiber separating/flying machine”, and the fibers are mixed homogeneously after separation and cutting of the fiber bundles. Various reinforcement mixed mats using carbon fiber (CF), glass fiber (GF), aramid fiber (KF) and thermoplastic matrix polyamide fiber (PA 6) were prepared by this method. Operating conditions of the machine for the preparation of the uniformly mixed mats, their properties and also compression molding conditions were investigated. Various mechanical properties of these composites were measured, and the influence of content of reinforcement fibers, their properties and orientation on the mechanical properties were discussed. The tensile properties of CF reinforced PA 6 composites did not increase monotonically with increasing fiber content, but rather decreased when flller content exceeded 20%, which seems to be due to a change in the fiber orientation.
KF reinforced PA 6 composites showed the highest impact strength and fractaure toughness of the materials investigated in this study, and it was found that KF is able to improve the fracture properties of CF and GF reinforced composites.

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Anisotropy in composition structure of injection-molded polypropylene plate filled with glass fiber was studied by means of measuring that thermal diffusivity. Two types of test films, whose thickness direction was vertical to melt flow direction (MD) or transverse direction to the melt flow (TD), were cut from the injection-molded plates, with a diamond cutter and a microtome. Glass fiber contents in the test films were 0, 5, 10 and 20 weight percent. Those thermal diffsivity was measured by a simple non-steady state method, using AC Joule heating, which had been developed in our laboratory. Then, the thermal diffsivity of injection-molded plate was evaluated as anisotropic in the place near the gate. Further, it was clarified by the obervation of dispersion and orientation states of glass fiber with polarizing light microscopy, that the orientation of glass fiber caused the anisotropy in the thermal diffusivity, rather than weight percent of the glass fiber.

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SMC Compression Moulding is used extensively today in manufacturing the outer panels and structural parts of transportation vehicles. In an effort to further decrease the power requirement caused by spherical stress tensor while maintaining cycle time, fabrication by rolling has been developed. A continuous uniform cross section by longitudinal rolling in progressive steps and by carrier type rolling using more complicated shaped dies driven by a coupling-roll unit. Actual moulded examples in T-shaped and channel shaped proflles indicate good surface quality and especially suitable fibre orientation.
Thr basic deformation behavior depends on the given conditions for the rolling process. The physical properties of the SMC due to the following characteristics of the SMC, that is, the heterogeneous nature and the laminate component.
As the SMC is a laminate, the initial rolling behavior of the macroscopic interface between plies with resin-rich surfaces should be considered. As the interface could be assumed discontinuous compared with the prepreg material, the deformation on the admissible stress field and stress field discontinuity in the cross section was analyzed to obtain the eigen modes.
The first problem is to control the flow and filling behavior during the fabrication process which is influenced by the rigid rotation due to different stiffnesses of fibre and resin at the microscopic interface covering each ply range.
The effects of feed rate on the flow pattern is a very important problem for the fabrication of different shape products. The selection of a lower value of feed rate generally gives better filling behavior for heterogeneous materials compared to homogeneous materials.

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