Fullerene derivatives were coated onto amorphous carbon substrates to modify carbon material surfaces, which have a great influence on the mechanical properties of carbon/epoxy composite such as carbon fiber reinforced plastics (CFRP). We previously reported that surface free energy of amorphous carbon was varied by coating fullerene derivatives onto amorphous carbon (a-C) substrates. However, the Adhesion strength of epoxy resin on the modified a-C substrates has not been clarified. In this study, mirror finished a-C wafers were used as carbon substrates. Fullerene derivatives were coated onto a-C substrates by spin-coating method. We investigated surface characteristics of the fullerene-coated a-C substrates by analysis of three surface energy components, dispersive, polar and hydrogen bonding force. Moreover, we evaluated the adhesion strength of the interface between the fullerene-coated a-C surface and the cured epoxy resin film by means of SAICAS method. These results indicated that there was a favorable correlation between the adhesion strength and the surface free energy on the fullerenecoated a-C substrate. We concluded that interfacial adhesion strength of carbon/epoxy could be improved by the coating of fullerene derivatives onto a carbon materials surface.

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The creep estimation using the time-temperature superposition principle has been considered by many researchers, they researched about the creep estimation with a single load. If you measure the physical properties of materials, it is just necessary to evaluate the viscoelastic property under the simple load. However in a practical scene, the multi-stage load was applied on the materials. Therefore, it is needed to calculate creep behavior with the response by a complicated load, but they weren't researched enough. Then, we considered about the applicability of the “Boltzmann's superposition principle” on the estimation of creep behavior and carried out the creep test with the multi-stage load conditions and estimated with the data from the single load creep behavior. The results of creep estimation were good agreement with the experimental creep data, and the little errors between estimated and experimental data were observed. It is, therefore, the estimation method using the linear visco-elastic theory and the “Boltzmann's superposition principle” can be applied to the estimation of creep behavior.

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In this paper, the effects of intensity of electron beam, variation with age after irradiation of electron beam on viscoelastic behavior of polypropylene resin (PP), which are widely used as medicine containers and so on, were investigated. Concretely, first, PP resins including colorant or not were prepared and samples that variously changed intensity of the electron beam irradiation were made. Viscoelastic test of samples which were irradiated and elapsed time after irradiation of electron beam was carried. The effects of those factors on viscoelastic behavior were discussed. The following results were obtained. (1) The viscosity of the PP resin is influenced from the electron beam irradiation though a colorant doesn't influence it. The viscosity decreases so that the larger strength of the electron beam irradiation is, the longer the time after it irradiates it is. (2) The storage modulus of PP resin is not influenced from the colorant, the electron beam irradiation and the elapsed time after irradiation. (3) The storage modulus of PP resin is not from the colorant and the electron beam irradiation and maintains the same time-temperature equivalent law.

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The dimensional accuracy of injection molded carbon fiber reinforced thermoplastics (CFRTP) was studied on the view point of viscoelastic behavior during molding process. First, the thermo-mechanical model was introduced to describe the thermo-viscoelastic behavior of CFRTP during molding process. Second, the warpage of CFRTP plate after molding was predicted for the typical cases of molding conditions by using the thermo-mechanical model. Third, the warpage of injection molded box made by thermoplastics and CFRTP were measured after molding process under various conditions. Finally, the mechanisms controlling the dimensional accuracy of injection molded CFRTP were discussed by comparing the predicted and experimental warps of its box.

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In manufacturing large-scale composite structure by means of vacuum assisted resin transfer molding (VARTM), the design of “process properties”, such as location of resin inlet and vacuum vent, is very important to prevent occurrence of dry-spot. If dry-spot occurred, then such defectives are normally destroyed. However, is it really impossible to reuse products with dry-spot? In this study, the interfacial bonding performance between undercured FRP and uncured resin was evaluated by lap-shear strength tests, which simulate the “reinjection” of matrix resin into dry-spot in fiber reinforced plastic (FRP) molded by VARTM. As a result, curing reaction was indicated in the interface between under-cured FRP and uncured resin. On the other hand, delamination was observed at the interface between after-cured FRP and uncured resin.

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In the present study, the tensile properties of silk fibers were determined through single tensile tests. The mechanical properties of silk fiber reinforced polybutylenesuccinate (PBS) biodegradable composites were also studied. The tensile tests of the long fiber unidirectional PBS biodegradable composites with different fiber volume fractions and fiber surface treatments were carried out. The effects of fiber surface treatments on the interfacial shear strength were conducted by pull-out tests. It was found that the effect of fiber surface treatment on the fiber mechanical properties is small. The experimental results showed that the tensile strength of SF/PBS composite increased when using fibers whose 46% of sericin is removed, but the fracture strain is not improved. However both the composite tensile strength and the fracture strain are improved when using fibers with ensui processing.

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In this study, we made a systematic detailed experimental observation on the damage growth behavior in 90° layer of cross-ply CFRP laminates. It is generally known that the crack initiation strain is increased with thinner 90° layer. However the mechanism has not been well clarified. We used a thin-ply prepreg developed by Sakai Ovex Co., Ltd with the theoretical minimum thickness of 40 μm. As a result of observation, the damage mode and the damage growth behavior are different depending on the ply thickness of 90°layer. It is shown that the damage growth is faster with thicker 90°layer (Mode A), while it is shower with thicker 90°layer (Mode B). In addition, It is observed that the crack opening displacement (COD) is larger in Mode A and smaller in Mode B. It is suggested that the damage growth behavior can be controlled with the ply thickness of 90°layer to explain the superiority of thin-ply CFRP laminates.

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This study describes a temperature dependence of transverse cracking in cross-ply CFRP laminates. A temperature-dependent transverse strength of the unidirectional composite is measured in order to discuss the temperature-dependent transverse crack occurring. The temperature dependence of transverse cracking is correlated with the temperature dependences of 90°layer strength and thermal residual stress in the cross-ply laminate under elevated temperature. The stacking sequence of the cross-ply laminates is also varied as a parameter. Whether the transverse crack occurs at relatively low load or high load at elevated temperature is then predicted considering the relationship between the temperature-dependent 90°layer strength and thermal residual stress.

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This paper is concerned with the influence of water absorption on the time-temperature dependent flexural fatigue strength of unidirectional CFRP laminates, which consist of PAN based carbon fibers and epoxy resin. The CFRP laminates were prepared under three conditions of “Dry”, “Wet(percentage of water content : 0.5%, 1.0% and 2.0%)”and “Wet+Dry” by dehydrating. The constant strain rate (CSR) and fatigue tests for these three kinds of CFRP laminates were carried out under various loading rates and temperatures. It is cleared that the flexural CSR and fatigue strengths of CFRP laminates strongly depend on the water absorption as well as time and temperature, and the time-temperature-water absorption superposition principle holds for these flexural CSR and fatigue strengths as well as the creep compliance of matrix resin.

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This paper is concerned with the influence of water absorption on the time-temperature dependent tensile strength of CFRP bolted joint. The CFRP bolted joint were treated under three conditions of “Dry”, “Wet (1.0%)” and “Wet+Dry” after molding. Tensile constant-elongation rate (CER) and fatigue tests for these three types of specimens were carried out under various loading-rates and temperatures. The influence of water absorption on time -temperature dependent tensile CER and fatigue strengths was evaluated, and the applicability of time-temperaturewater absorption superposition principle (TTWSP) as well as time-temperature superposition principle (TTSP) was discussed. As results, it was cleared that the tensile CER and fatigue strengths of the CFRP bolted joint depend on water absorption as well as time and temperature, and that TTWSP does not hold always for that strength of these specimens, although TTSP holds for these strengths.

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A cost planning method of manufacturing is vital for achievement of affordable composite design and production. Major two composite manufacturing processes, autoclave and RTM, were programmed on PC and cost modeling & simulation case studies were conducted with three composite aircraft parts which consist of flat panels and ribs. The keys for development of the methods are holistically discussed and proposed through the case studies : 1) precision of critical variables, 2) particular issues in composites and 3) goals as a planning tool.

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