In this study, the single fiber composite was used to evaluate the stress transfer between a single fiber and a matrix. Single steel fiber was inserted to the epoxy resin, and the tensile load was applied to the steel fiber. Applied load was varied from 0N to 177N, and then the photoelastic images were taken by a digital CCD camera. On the photoelastic analysis, the stress separation was carried out using an experimental-numerical hybrid method. The boundary conditions for a local finite element model, that is, the tractions along boundaries were inversely determined from photoelastic fringes. After determining the boundary conditions for the local finite element model, the stresses could be obtained by finite element direct analysis. The maximum shear stress were placed on the side surface of the steel fiber near the end of fiber, and the maximum normal stress difference was measured near the surface of the end of fiber. The results of stress distribution on the interface between the fiber and the resin indicated that the stress concentration was observed on the middle part of the end of fiber and the side surface near the end of fiber.

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   This paper introduces “Tapping AE method” which is a new Non-destructive testing method for Carbon fiber reinforced plastic (CFRP). Although it has many advantages, internal damage easily occurs in CFRP components even by a small out-of-plane load. The typical non-destructive methods for CFRP are ultrasonic testing (UT) and tap testing. Although UT has high detectability, UT is a time and cost consuming method. On the other hand, tapping method is a quick and easy way to conduct, although, the detectability is insufficient. The aim of developing tapping AE method is realizing high-detectability tap testing. In Tapping AE method, the specimen is tapped by a hammer and secondary AE emitted from the damages are measured by AE sensor installed in the hammer during the hammer tapping. In order to evaluate feasibility of tapping AE method, we developed tapping AE system. The test was applied to a cross-ply CFRP laminate with and without internal damages. During the test, we observed secondary AE signals from the damaged specimen. New parameter, RMS_ratio was defined to evaluate secondary AE signals. Compared with the result of traditional tapping method using contact duration, the result of proposed method using RMS_ratio shows high detectability.

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   Mechanical quantity sensor made of laminated rubber sheet is used as a load sensor. Also, it can be flexed so the evaluation of the bending characteristic by a bending test was carried out. The bending test equipment was manufactured in order to carry out the test. As the result of the bending test, it was found that the relation between the voltage output of the sensor and an angle of the test piece is linear. Also, the bending characteristic under various conditions of gauge length, width, thickness, and structure of silicon rubber were investigated. Additionally, the bending simulation of the laminated rubber sensor by FEM was performed in order to consider new structures or materials. The boundary condition for the bending simulation and evaluation method has been proposed. The result of the bending simulation was in good agreement with the experiment by using the proposed equation. Moreover, the characteristic of the multistage bending was evaluated experimentally and analytically, and the result according to the theory was obtained.

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   In this study, three-point bending tests were performed for discontinuous glass fiber reinforced plastic composite material. Specimens with both unspread and spread fiber bundles were used. In specimens with unspread fiber bundles (unspread specimens), fiber bundles (fiber length is about 12mm) is randomly-oriented. In specimens with spread fiber bundles (spread specimens), fibers are spread (fiber length is 4-6 mm) and no fiber bundle is observed in the specimens. In order to investigate the difference in damage behavior in unspread and spread specimens, damage growth behavior was observed by an optical microscope and acoustic emission (AE) behavior was monitored during bending test. In the unspread specimens, the stress-deflection curves showed nonlinear behavior which is due to the initial crack formation in fiber bundles whose fiber direction is almost perpendicular to the tensile stress. The stress-deflection curves also shows the intermittent stress reductions which corresponds to the crack growth at the fiber bundle interfaces. In the spread specimens, the stress-deflection curves showed almost linear behavior which reflects the fact that few damage is observed until the maximum stress is reached. It was also found that the spread specimens showed higher strength than the unspread specimens. The results of AE monitoring were well correlated with the stress-deflection curves and the optical damage observation.

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   Carbon fiber reinforced plastic (CFRP) laminates are used in various industrial fields because they have excellent properties such as a specific strength and a specific stiffness. The use of CFRP in the manufacture of automobiles can lead to a significant reduction in automobile weight, thereby improving the vehicle mileage as well as reducing CO₂ emissions. On the other hand, the issue of passenger safety in case of collisions should also be clarified when employing CFRP in the fabrication of automotive structures. The objective of this study is to investigate the response behavior and energy absorption characteristics of CFRP/Steel hybrid plates which consisted of a steel and three types of CFRP laminates under low-velocity impact bending load. We performed drop weight impact tests under the boundary condition of three point bending; the tests involved dropping an impactor from a height of 1.5 m so that the impactor speed just before impact was approximately 20 km/h. With regard to the impact response behavior and absorbed impact energy, the UD-0 specimen showed better performance than the other specimens.

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   This paper presents an eddy current-based approach for detection of delamination in carbon fiber-reinforced plastics (CFRPs). It has been difficult for conventional eddy current testing to detect delamination because delamination is parallel to eddy current paths. The authors proposed induction heating assisted eddy current testing (IHAET) for delamination detection. In IHAET, surface of the material under test is heated by induction heating coil to cause temperature difference between intact zone and delamination zone. Delamination can be detected by electrical conductivity measurement of eddy current testing utilizing the temperature dependence of conductivity. In this paper, heating and temperature measurement of materials was carried out in transmission mode to reduce the lift-off effect. In addition, surface temperature of CFRP was measured by eddy current testing probe at near resonance frequency to improve sensitivity of thermo-sensing. Experimental studies prove that sensitivity of thermo-sensing can be improved by using a resonant probe compared to our previous work. We found that measurement of reactance of thermo-sensing coil offers higher sensitivity due to the resonance frequency shift caused by variation of material’s conductivity. Furthermore, 10 mm wide delamination 2 mm away from the surface of 4 mm thick CFRP could be detected by the proposed method.

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   A ray tracing method is applied to measure residual stress in a transparent PMMA specimen. A laser beam enters into the PMMA specimen and propagates in it. The laser beam changes its propagation direction slightly, caused by the change of refractive index of PMMA due to the residual stress. Measuring the laser beam trajectory gives the distribution of residual stress in the specimen by means of ray tracing equation. The measurement results say that the residual stress near specimen surface is compressive stress and the maximum value is about 11MPa. This value is much smaller than the fracture strength of 79MPa of PMMA, however, may not be negligible in accurate experiments to verify a theory of fracture mechanics.

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   The purpose of this study is to propose predictive method of the measuring precision of the depth measuring microscope using a technique that combines a whole-space tabulation method (WSTM) and light-source stepping method. The WSTM excludes almost all of systematic errors such as the influence of a lens distortion and deformation of the brightness distribution of the projected grating from the measured result. Therefore, it becomes possible to predict the precision of a measurement device by only considering the random error caused by camera noise and caused by reflectance characteristics of the surface of an object. In this study, a precision prediction method for depth measuring microscope using grating projection method is proposed. The effectiveness of the predictive method is verified by comparing the predicted precision and the measuring precision. The theory and experimental results are shown.

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   From the viewpoint of surface quality, the jet wiping method, that is a non-contact type, is used to control the coating thickness in a continuous galvanizing line. In this paper, in order to study influences of nozzle tip angles on the wiping ability, we conducted wiping tests using a wiping simulator and CFD analysis to examine the jet properties. Furthermore, we observed the shape of the liquid film in the vicinity of jet impingement. The wiping tests revealed that the nozzle tip angle had a large influence on film thickness. A thickness increase of approximately 20% was observed at a tip angle of 90° compared to 50°. But there were no changes in impingement pressures and shear stresses in both measurements and CFD analysis. On the other hand, the film shapes changed, becoming thicker when the tip angle was increased. Therefore, the change of liquid film thickness is inferred as the main reason for wiping performance changes by nozzle shape.

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   On March 11, 2011, a very big earthquake occurred in the Tohoku district in Japan. As a result, a large amount of tsunami sludge was generated and radiation contamination due to Fukushima nuclear disaster also became a serious problem. Therefore, it became necessary to be stored the radioactive pollutant at temporary storehouses after the decontamination of the radiation-contaminated waste and soil. However, the embankment made of ordinary soils had low strength property due to rainfall and low quake-resistant ability; the rainwater seepage control sheets were also affected by the ultraviolet light. Therefore, further improvements on these solutions were required. In this study, we focused on the application of Fiber-cement-stabilized soil method to the cover soil for radiation-contaminated soil. Moreover, the setting method of optimum conditions for creating Fiber-cement-stabilized soil made of tsunami sludge was developed based on the compaction characteristics of the tsunami sludge. The advantage of the developed method was validated by laboratory soil test. As a result, the developed method was useful for easily-setting the optimum condition for creating the Fiber-cement-stabilized soil by recycling the tsunami sludge.

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   An experimental study on the stabilization of coral-gravel beach was performed using carbonate precipitation induced by microbial urease activity. The pilot experiment was done to solve scale-up problems from the bench scale experiments. In this study, microbes, ureolytic strains NO-A10 isolated from the domestic soils, were used to induce the hydrolysis of urea. The product of the hydrolysis was used to produce carbonate which acts as a binder (bio-cement) for coral gravels. The 70 cm thick coral gravel layer was cemented by injecting the bio-cement solution. The result showed that the gravels were strongly cemented with the carbonate precipitated. However, the experimental results could not be quantitatively predicted from the bench scale experiment. In this study, scale-up problems are discussed in terms of size effect, reaction velocity, distribution of microbes, transport distance of microbes, etc. This study will contribute to the success for actual construction.

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[in Japanese]

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