The time and temperature dependent static strengths for typical three directions of unidirectional CFRP, which are the tensile and compressive static strengths for the longitudinal direction and the tensile static strength for the transverse direction, were measured at various deformation rates and temperatures in our previous papers. By using these measured data, the master curves of these static strengths are constructed based on the time.temperature superposition principle to be held for the viscoelastic behavior of matrix resin. Furthermore, the relationships between the viscoelastic behavior of matrix resin and these static strengths are evaluated on the viewpoints of failure mechanism. The quantitative characteristics of these static strength master curves are discussed using the formulation based on their failure mechanisms.

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Mechanical properties and dimensional accuracy of FRP parts depend on molding process. In this study, a simulation method considering molding process to predict those of FRP parts has been developed. In this paper, some new characteristics were proposed to analyze curing process of the matrix because after cure effect and cure shrinkage would affect the deformation and residual stress in the FRP parts. The characteristics data to predict cure temperature corrected by after cure effect were acquired experimentally by evaluating the proportions of the thermal deformation of CFRP laminates molded by after cure process to those of them molded by no after cure process. And the new parameters to predict the deformation of CFRP parts caused by cure shrinkage were acquired experimentally by evaluating the cure shrinkage strains of CFRP and contribution of resin cure shrinkage to deformation of CFRP laminates.

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This paper discusses relationships between electrical properties of Ni particle dispersed high-density polyethylene (HDPE) composites and Ni content and weight-average molecular weight (Mw) of HDPE. We also investigate conductive path structures formed by Ni particles based on results from SEM observation and percolation model analysis. The ρL (resistivity at room temperature) decreased with increasing Ni content, and these behaviors consisted with percolation behavior. Percolation threshold decreased with decreasing Mw of HDPE. Crystallinity of HDPE increased with decreasing Mw of HDPE. It was expected that Ni particles are concentrated spatially in amorphous region of HDPE. Therefore, percolation threshold decreased with increasing crystallinity of HDPE due to decrease of Mw of HDPE. The temperature of positive temperature coefficient (PTC) effect (inflection point of PTC curve) decreased with decreasing Ni content. It is considered that lower Ni content leads to disconnection of conductive path because conductive path becomes much less with decreasing Ni content. When Ni content is the same, the temperature of PTC effect rose with decreasing Mw of HDPE. This was due to increase of crystallinity of HDPE by decreasing Mw of HDPE.

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This paper aims at investigating the effect of mechanical properties on high-velocity impact damage in CFRP (Carbon Fiber Reinforced Plastic) laminates. Dynamic finite element analysis is performed to achieve this end. Cohesive elements are introduced to express the delamination and splitting cracks while the maximum stress fracture criteria are employed to express the intralaminar failure in the analysis. Four material properties such as fiber strength, fiber elastic modulus, interlaminar strength and interlaminar fracture toughness are changed in the analysis as presumed dominant parameters. It is found that an increase in interlaminar strength rather than that in the interlaminar fracture toughness constrains delamination and that the fiber elastic modulus has the greatest effect on the perforation limit.

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Recently, green composites (GC) using natural fibers and biodegradable resin have been developed and investigated, aiming at contribution to preservation and improvement of the global environment. However, in composites using biodegradable resin as matrix, it is considered that the degradation by hydrolysis might be selectively accelerated at the interface. In the present study, we aim to clarify the local hydrolysis behavior at interface in fiber reinforced plastics using biodegradable resin as matrix. Here, we prepared a new type of GC model specimen, where the inside interfacial debonding can be observed directly, using a glass rod (GR) as fiber and polybutylene succinate adipate (PBSA) as matrix. In-situ observation of the internal interfacial debonding behavior was carried out during tensile tests of GC model specimens after immersion into water within the range of 3 weeks of immersion time, where the tensile strength of PBSA matrix itself was not degraded. In addition, experimental results were discussed combined with a simple finite element analysis. As a result, it was demonstrated that the hydrolytic degradation speed of interface was much higher than that of matrix resin. It was considered that water molecules diffused in the free volume of resin and locally accumulated at the interface between fibers and resin, resulting in the acceleration of hydrolysis at the interface.

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The heat exchanger designed for a boiler exhaust gas near the sulfuric acid dew point was examined with carbon fiber reinforced phenol FRP. The evaluation of physical degradation by mechanical strength shows mechanical properties degraded step by step, and “S” element analysis on the specimen cross section indicated permeation/ diffusion mechanism of the environment into CFRP at high temperature and high concentration condition. The evaluation of chemical degradation by IR analysis was also carried out based on time temperature superposition principle. The IR-index data from many temperature and concentration conditions were well obeyed to the law. Life estimation was examined and the change of flexural strength was well estimated by this method.

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The effects of temperature difference and interlayer thickness on the thermal fatigue life of S45C/Cu/Si₃N₄ composites with brazing filler metals of AgCu and AgCuTi are described. First, specimens of S45C/Cu/Si₃N₄ systems with interlayer thicknesses of 150 and 200 μm were prepared by brazing. Next, thermal fatigue tests were conducted under cyclic heating conditions with temperature differences of 25-300 and 25-600℃. Further, fatigue fracture surfaces due to the cyclic thermal loadings were observed using an optical microscope. The results revealed that cyclic thermal loading(25-300℃)of the composites caused fatigue failure to the brazing filler metal or Cu/Si3N4 interface. In contrast, cyclic thermal loading with the relatively large temperature difference caused fatigue failure to not only Cu/Si₃N₄ interface, but also S45C/Cu. These results indicated that the fatigue damage of the composites depended on the thermal stress amplitudes around the interfaces. The thermal fatigue life decreased logarithmically with an increase in temperature difference, and was found to obey Manson-Coffin's law. The increase in the thickness of interlayer contributed to the extension of thermal fatigue life. In addition, a model was proposed for evaluating the thermal fatigue life of the composites, and the effects of temperature difference and interlayer thickness on the thermal fatigue life were discussed using the model.

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A method for evaluating stress components from interferometrically measured isopachics around a hole in a plate is proposed in this study. A Poisson equation that represents the relationship between the sum of principal stresses and an Airy stress function is solved using a finite element method. The Dirichlet boundary condition for solving the Poisson equation is determined by the approximation of an assumed Airy stress function along the boundary of the model. Therefore, the distribution of the Airy stress function is obtained from the measured isopachic contours. Then, the stresses are obtained from the computed Airy stress function. The effectiveness of the proposed method is validated by a simulation and an experiment. Results show that the stress separation of isopachics around a hole is possible by the proposed method.

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Using environmentally friendly wet ozone instead of conventional chemical methods, we removed positive-tone novolak resists. In wet ozone process, resists were decomposed and were removed in the process of the ozonolysis reaction of resists and the hydrolysis reaction of the ozonolysis products. Wet ozone process has the combination of wet ozone temperature and substrate temperature which photoresist removal rate becomes maximum rate. The maximum photoresist removal rates are 1.8μm/min at wet ozone temperature was 74℃ and substrate temperature was 66℃, 1.6μm/min at wet ozone temperature was 68℃ and substrate temperature was 62℃, 0.9μm/min at wet ozone temperature was 46℃and substrate temperature was 44℃. It was revealed that temperature difference (= “wet ozone temperature (TWO)”. “substrate temperature (TIS)”) to control water requirements for the hydrolysis strongly influences the resist removal rate. Also, the reaction of photoresist removal using wet ozone accedes to arrhenius low, and activation energy was 28.0kJ/mol.

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