Papers by Author: Koichi Goda

Abstract: T wisted yarns are used for bio-composites and nanocomposites as reinforcement . In a twisted yarn, single yarns migrate from surface to inner along the yarn axis. In this research , migration structure is studied by using X-ray CT system . The result is obtained that the orientation angle correlates with layer .

Abstract: This paper describes an effect of fluctuation in fiber orientation on the tensile properties of sliver-based green composites. The composites were reinforced with slivers of high-strength natural fibers extracted from plants named curaua. Then a surface optical micrograph of the composites with the fiber fluctuation was obtained. The micrograph was divided into many fine segments, and the fiber orientation angle in each segment was measured. Results show that the tensile strength depends on autocorrelation coefficients expressing the degree of fluctuation in fiber orientation, as well as the fiber orientation angles. However, the Young’s modulus was dependent only on the angles, rather than on autocorrelation coefficients. In addition, a statistical concept was applied to an orthotropic analysis for prediction of the Young’s modulus. The predicted Young’s moduli showed better agreement with the experimental results.

Abstract: This paper describes an effect of fluctuation in fiber orientation on Young’s modulus of the so-called green composites. The composites were reinforced with slivers of high-strength natural fibers extracted from plants named curaua. Then a surface optical micrograph of the composites with the fiber fluctuation was obtained. The micrograph was divided into many fine segments, and the fiber orientation angle in each segment was measured. Then, a new concept which takes account of the fiber orientation angles as a probability distribution, was proposed for prediction of the Young’s modulus. The results showed that the predicted Young’s moduli were in a good agreement with the experimental results.

Abstract: Nowadays, natural fiber-reinforced green composites are increasingly being used in the industrial field. The strength of natural fibers is often evaluated on the assumption that the fibers’ cross-sectional shape is circle, but this is rather observed as an ellipse. In the present study, therefore, we propose a new method to calculate the cross-sectional area of natural fibers by measuring their projection widths. In addition, we propose a strength distribution function with taking account of variation in cross-sectional area, based on Weibull distribution, and discuss the validity of the proposed distribution function.

Abstract: The tension-tension fatigue tests for SiC/SiC composites were performed under the conditions that the maximum load Pmax was 80-90% to the fracture load of the tensile tests and the stress ratio was Rσ = 0.5. The composites exhibited a width in stress-strain hysteresis loop under one load cycling. In some cases the mean strain εmean gradually increase with increasing in number of cycles. These variations would reflect the developments of the fatigue damage at the fiber/matrix interface during the cyclic loading process. The pull-out lengths of the fibers for the fatigued- and not fatigued-specimens were measured through the SEM observations after the tensile test. In all materials, the average pull-out length of fibers in fatigued material was larger than in not fatigued material because the cyclic loading affected on the fiber/matrix interfacial strength.

Abstract: Environment-friendly green composites were developed by combining a biodegradable resin with curaua fibers. The composites were fabricated by three different methods, i.e. direct, pre-forming and prepreg sheets methods. Mechanical properties of composites fabricated by all three methods were evaluated through tensile test. Moreover, green composites reinforced by fibers treated with high concentration alkali solution were fabricated by pre-forming and prepreg sheets methods. The results showed that fracture strain of alkali-treated fiber composites increased twice to three times larger than that of untreated-fiber composites. Finally, effect of cyclic load application on tensile strength of curaua single fibers was investigated.

Abstract: Biodegradable composites made from bagasse fiber and biodegradable resin were prepared and the biodegradation were investigated by the soil burial test in terms of the effects of fiber content, alkali treatment to bagasse fiber and different soil. The biodegradable resin showed some extent biodegradation. The addition of bagasse fiber caused the acceleration of weight loss of the fiber reinforced composites in comparison with the neat biodegradable resin. The weight loss of the composites increased with the increase in the fiber content, which could attribute to the preferential degradation of bagasse fiber and the resin around the fiber. However there was no significant difference in weight loss between untreated and alkali treated fiber composites. Furthermore, it is noted that the weight loss drastically increased in the case of the composites buried in the microorganism enriched soil. This results from the increase of bacteria and fungi in soil. The photographs and SEM micrographs showed the degradation of the resin and the composites.