Akiyoshi Takeno

Volume fraction and temperature dependence of mechanical properties of silicone rubber particulate/epoxy blends

Abstract At all temperatures, both the Youngs modulus and tensile strength of silicone rubber particle/epoxy resin blends decreased as the volume fraction of the silicone rubber particles was increased, and this decrease became greater with falling temperature. A volume fraction-temperature superposition held for both the Youngs modulus and tensile strength of the blends. The shifted volume fraction of silicone rubber particles needed to obtain master curves increased with increasing temperature and the shift was almost the same for both properties. An optimum suitable volume fraction of rubber particles existed in terms of improving impact fracture energy. A volume fraction of silicone rubber particles of 5–10% appears to be the most suitable for obtaining a blend in which the decrease in Youngs modulus and the tensile strength is relatively low and the increase in impact fracture energy is relatively high.

FATIGUE BEHAVIOR OF ARAMID NONWOVEN FABRICS UNDER HOT-PRESS CONDITIONS. PART I : MECHANICAL PROPERTIES

Tensile and compressive behaviors of aramid and polyamide nonwoven fabrics are studied under hot-press fatigue conditions. Tensile breaking strength and the maximum modulus of tensile strength-elongation curves for the polyamide nonwovens gradually decrease with increasing fatigue after around 15 cycles, while those of the aramid nonwovens substantially increase. Aramid nonwoven values are about three to five times those of the polyamide nonwovens. These fatigue behaviors result from the differences in heat resistance and mechanical properties of polyamide and aramid fibers, indicating that polyamide fibers greatly deteriorate with heat while aramid fibers deteriorate only a little. Although we have assumed that the aramid nonwoven fabrics compact their fiber assemblies under increasing cycles, there are no substantial dif ferences in the compressive behaviors of polyamide and aramid nonwovens.

Anisotropic transparency of polystyrene film with crazes

A crazing method was developed to create regular crazes in a polystyrene film. The crazes penetrated completely in the direction of film thickness. The tensile strength of the crazed films in both perpendicular and parallel directions to the processing direction was almost unchanged after the crazing-processing, regardless of crazing conditions. Youngs modulus in the parallel direction decreased with the film tension during the crazing-processing. If suitable crazing-processing was used, transmittance of incident light decreased between the incident angles of 0 to 20 deg, and increased above the angle of ca 20 deg with an increasing incident angle, which gives a W-shape to the light transmittance curve.

Strain rate and temperature dependence of shear properties of epoxy resin with various molecular weight between cross-linkings

Epoxy resins with various molecular weights between cross-linkings were prepared. In order to examine the strain rate and temperature dependence of the shear yield strength and the shear strength, test specimens were subjected to shear deformation at various strain rates and temperatures. The shear yield strength and the shear strength increased almost linearly as the logarithm of the strain rate increased. The strain rate-temperature superposition held for these shear properties. In particular, an experimental equation of the strain rate-temperature superposition for the shear yield strength was found. The shift factor to obtain a master curve was given with the temperature dependence of an Arrhenius type. Furthermore, the strain rate-temperature-molecular weight between cross-linkings superposition held for the shear properties.

Mono-component poly(vinylidene fluoride) composites by craze structural control

A method to generate crazes uniformly and regularly with ordered structures was developed to fabricate mono-component polymer composites that mixed regions of different high-order structures. Crazes with regular structure were generated in PVDF films. Although crazes penetrated completely in the direction of film thickness, no degradation of the tensile strength of the film was observed either in perpendicular or parallel directions. Youngs moduli showed a tendency to decrease in the direction perpendicular to the crazes and the loss of energy increased significantly. Because crazes generated in PVDF films scattered the incident light beams just like blind feathers, it was possible to obtain films that were transparent from the view field perpendicular to the crazes but opaque from view angles larger than 30 degrees.