Papers by Author: Akihiko Yamaji

Abstract: Mechanical properties of nano/micro-silica particles bidispersed epoxy composites were investigated based on experimental results. The composite specimens varied with different compositions of nano and micro-silica particles (240 nm and 1.56$m) were prepared with the constant volume fraction, 0.30. The thermo-viscoelastic properties for the composites and the neat epoxy measured in the temperature ranges from 123 K to 523 K and compared to theoretical results according to Lewis and Nielsen’s law with the maximum particle packing given by Ouchiyama and Tanaka’s model. In addition, fragility derived from the thermo-viscoelasticity measurements was used to characterize the strength and fracture toughness of the composites. From results, we found that the thermo-viscoelasticity of the composite was dependent on nano and micro-particles packing, and its strength and fracture toughness were effectively evaluated by fragility.

Abstract: This paper investigated the initiation and propagation characteristics of impact-induced damage in carbon-fiber-reinforced-plastic (CFRP) laminates with different stacking sequences and thicknesses under low-velocity impact. Impact force histories were measured with a drop-weight impact tester. A strain gauge was attached on the back face of CFRP laminates to measure exactly when a matrix crack on its back face was initiated. It was found from fractographic observation that impact-induced damage in CFRP laminates was initiated at the matrix crack on the back face of CFRP laminates due to bending deformation during impact. Finite element analysis was conducted using the impact forces derived from the experimental results of the impact test. Its results clarified that the tensile stress normal to the fiber on the back face of the specimen was the criterion to initiate impact damage in CFRP laminates.

Abstract: The development characteristics of impact-induced damage in carbon-fiber-reinforcedplastics (CFRP) laminates were experimentally studied using a drop-weight impact tester. Five types of CFRP laminates were used to investigate the effect of stacking sequences and thicknesses. The efficiency of absorbed energy to impact energy was different for CFRP laminates with different stacking sequences or thicknesses. The DA/AE ratio of delamination area (DA) to absorbed energy (AE) was almost the same for CFRP laminates with the same stacking sequence regardless of the thickness. We found that the DA/AE ratio could be used as a parameter to characterize the impact damage resistance in CFRP laminates with different stacking sequences.

Abstract: We investigated the particle size effects on the fracture toughness of epoxy resin composites reinforced with spherical-silica particles. The silica particles had different mean particle diameters of between 1.56 and 0.24µm and were filled with bisphenol A-type epoxy resin under different mixture ratios of small and large particles and a constant volume fraction for all particles of 0.30. As the content with the added smaller particle increased, the viscosity of each composite before curing remarkably increased. We conducted the single edge notched bending test (SENB) to measure the mode I fracture toughness of each composite. The fracture surface with the small particle content exhibited more rough areas than the surface with larger particles. The fracture toughness increased below the small particle content of 0.8 and saturated above it. Therefore, near the small particle content of 0.8, the composite had a relatively low viscosity and a high fracture toughness.

Abstract: We experimentally investigated compressive behaviors of a paper and a paper coated by polyethylene resin. The initial thickness of sheets of paper measured under a compressive stress of 4.5kPa was widely distributed in comparison with the basis weight, although the results based on the ISO 534 standard (under compressive stress of 100kPa) had relatively little dispersion. For compressive deformation, the thickness immediately decreased under low compressive stress, because the gap between fibers in the paper collapsed. After that, the variation of the thickness under higher compression was small due to the compression of fibers. We found that although the resin-coat layers did not have an insignificant effect on compressive compliance above 250kPa, the compliance of the coated paper was larger than that of uncoated paper.