Papers by Author: Toru Fujii

Abstract: The purpose of this study is to reveal the effects of the modification of the sheet of Polypropylene (PP) with fine glass fibers for repair of the Carbon Fiber Reinforced Thermo Plastics (CFRTP) on the recover ratio of degraded mechanical properties of damaged CFRTP after impact bending. Impact damaged specimen was repaired by inserting tiny melted sheet of PP modified with fine glass fibers to be assimilated with PP matrix around the surface of damaged area. Model specimens having cut reinforcements were prepared for compressive buckling tests to investigate the effect of the modification on mechanical behaviors under compressive stress due to the impact bending. The recovering ratio defined as the ratio of compressive buckling strength of damaged model specimen to that of un-damaged specimen was investigated. The recovering ratio of model specimen after the repair was about 49% when the unmodified PP sheet was used to repair. On the other hand, when the weight content rate of fine glass fibers was 2.0wt%, about 73% of recovering ratio was successfully obtained. The appropriate condition of the weight content rate was shown for repairing the damaged part of the CFRTP used in this study.

Abstract: Plain woven carbon fabric composites using different types of vinyl ester (VE) resin with different toughness have been prepared. The mechanical performances were characterized by different tests, such as tensile, tension-tension fatigue, thermoelastic stress analysis (TSA) and scanning electron microscope (SEM). The results showed that with increasing of fracture toughness of VE as well as adhesive strength between VE and carbon fiber (CF), the tensile strength improved by a range from 23.1 to 33.9%, and fatigue life of CF/VE composites increased by several times to several ten times when low toughness VE was used as control resin. The fatigue damage initiation of CF/VE composites has been investigated by thermoelastic stress analysis. It was found that the initiation and growth of fatigue damage such as matrix cracks was delayed, the linkage of matrix cracks in transverse bundles was inhibited with increasing of fracture toughness and interfacial shear strength (IFSS) of matrix resin.

Abstract: The typical speaker for cellular phone is composed of magnet, coil, base-film and diaphragm with a structure that laminated a foam sheet and aluminum sheets. A heterogeneous foam sheet which has an uneven elastic modulus was used for a conventional diaphragm, and it reduced an acoustic performance of a conventional speaker. Recently a homogeneous and thin foam sheet was newly developed. The purpose of this study is to improve the acoustic characteristics of the micro speaker by changing thickness and foaming ratio of the newly developed foam sheet. Frequency characteristics and sound pressure level (SPL) were measured by changing foaming ratio of the foam sheet from 2.5 to 5.0 and thickness of the foam sheet from 0.15 mm to 0.30 mm. To clarify the relationship between the design parameter of foam sheet and the frequency characteristics of the micro speaker, natural frequency analysis using finite element method (FEM) was performed. The result of FEM analysis was also compared with the experimental result using a laser doppler velocimetry sensor. It was found that the widest reproducible frequency range was obtained when the foam sheet was used 0.30 mm of thickness and 5.0 of foaming ratio. The reproducible frequency range spread out 15% in comparison with that of a conventional micro speaker.

Abstract: The purpose of this study is to provide a simple method for estimating the driving resistance of rubber conveyer belts. The driving resistance of a rubber belt running on the carrier roller was estimated by a resistance force acting on a roller moving on the rubber conveyer belt while the belt was fixed on an aluminum channel. Four types of conveyor belts were tested to confirm the present technique is useful for grading rubber conveyer belts from a viewpoint of energy dissipation on the carrier rollers of the conveyer system. The effects of normal force acting on the roller and driving speed of the roller on the resistance force were investigated. Four belts were fabricated with different rubber types of rubber, respectively. It was confirmed from the experiments that the estimated resistance force varied with respect to the rubber characteristics, which was consistent to the experience from the existing belt conveyer systems for energy consumption. The resistance force of the carrier roller increases with an increase of roller speed. It also decreases when a lower damping rubber is used while the belt rigidity does not affect the resistance force when low resistance rubber is used. The proposed method is applicable to estimate the total energy loss of rubber conveyer belts on the carrier rollers.

Abstract: Carbon fiber (CF) reinforced compositesusing different types of vinylester (VE)resin includingconventional VE resinhave been prepared. The mechanical performance were characterized by different tests, such as tensile, mode-I interlaminarfracture toughness, tension-tension fatigue and scanning electron microscope (SEM).The experimental results showed that the tensile strength of CF/VE composites changed at a wide range from 22.3% to 37.8% in comparison with the CF/conventional VE composite due to resin type, where the strain at failure was varying. The tensile strength increased with an increase of adhesive strength between carbon fiber and VE resin characterized by the microdroplet test. Namely, a good correlation between the tensile strength of composites and the adhesive strength was found. On the other hand, almost an inverse correlation was found between the tensile strength of composites and the interlaminar fracture toughness of composites obtained by DCB (double cantilever beams) tests. There was no apparent correlation found between the strain at failure for pure resins and the tensile strength of composites.Thefatigue life of CF/VE compositesincreased as well as the tensile strength with an increase of the adhesive strength between carbon fiber and the resin. The samples sometime survived 1000 times longer than that of CF/conventional VE compositewhen the maximum cycle stress was 70% of the tensile strength of the strongest composite.

Abstract: Significant stiffness reduction of the plate spring due to delaminations around the interwoven cloths could be prevented by using CFRTP (carbon fiber cloth and Polyethylene Terephthalate (PET)) rather than that by using CFRP (carbon fiber cloth and epoxy), when ultra high cyclic loading was applied to the plate spring under high humidity condition. To explain the result, the prediction model of stiffness reduction was introduced considering time-dependent crack propagation accompanying with creep deformation around the crack tip. Stiffness reduction of CFRP under high humidity condition was not only determined by cyclic crack propagation but also by time-dependent crack propagation accompanying with creep deformation around the crack tip. It was found that CFRTP was effective material of the plate springs on vibration conveyer for the uses under high humidity condition to prevent significant stiffness reduction, where the crack propagation accompanying with creep deformation should be prevented around the crack tip.

Abstract: This paper investigated the stiffness reduction of the plate spring made of CFRP (Carbon cloth and epoxy) subjected to ultra high cyclic fatigue loading under high relative humidity. For practical uses, this paper proposes a new design which prevents the significant degradation with stiffness change of the plate spring at high humidity. Remarkable stiffness reduction of the plate spring due to cracks and delaminations around inter layer could be prevented by using CFRTP rather than that by using CFRP, when ultra high cyclic loading was applied to the plate spring under high humidity condition.

Abstract: This study investigated the effect of the enhancement by addition of Micro Fibrillated Cellulose (MFC) on the static, fatigue and impact properties of plain-woven CFRP. Test results showed that the addition of MFC little contributed to the improvement of static properties. However, the initiation of matrix cracks between woven carbon fiber cloths was prevented under cyclic loading so that the fatigue life of the CFRP was improved by the modification with MFC. The ductility of plain-woven CFRP was also acquired under impact load by the addition of the MFC to the matrix.