The purpose of this study is to stabilize the coefficient of friction of carbon-carbon (C/C) composites through wide environmental temperature range by synthesizing the carbon nanotubes (CNTs) on its surface and inner pore. In this study, conventional CFRP was carbonized at 2,200˚C with inert atmosphere to fabricate the C/C composites in which char matrix was made from phenolic resin. CNTs were synthesized on the surface and inner pore of fabricated C/C composites by the thermal chemical vapor deposition method. The coefficient of mutual friction and wear amount between two flat specimens were measured at a constant rotational speed under constant applied pressure by using the disc-type test apparatus. The effect of CNT synthesization on the mutual friction coefficient and its dependence on test temperature were discussed. Frictional coefficient was high and also stable when the CNTs were synthesized on surface and inner pore while the test temperature was changed. The wear amount of modified C/C composites was almost same as that of unmodified one. Test results also showed that the variation of friction coefficient of modified C/C composites during frication test was explained by the variation of local volume fraction of matrix of C/C composites.
A novel experimental method was proposed for characterizing the compressive properties of composite materials under impact loading. Split Hopkinson pressure bar system was employed to carry out the dynamic compression tests. The dynamic stress-strain relations could be precisely estimated by the proposed method, where the ramped input, generated by the plastic deformation of a zinc buffer, was effective to reduce the oscillation of the stress field in the specimen. The longitudinal strain of gage area could be estimated from the nominal deformation of gage area, and consequently the failure process could be grasped in detail from the stress-strain relation. Finite element analysis was also carried out to confirm the validity of the proposed method. Numerical results demonstrated that the nonuniformity of the stress field could be negligible by using the ramped input. The dynamic compressive strength of a twilled-woven carbon-fiber/epoxy composite was slightly higher than the static compressive strength.
This study aims to reveal the mechanism of melting and oxidation phenomenon of CF/PPS laminated composites by electrically-conducting. The materials used are unidirectional CF/PPS and woven CF/PPS laminates. The effects of applied voltage, conducting time and fiber reinforcing configuration on melting behavior of CFRTP composites were investigated. The melting state was evaluated by microscopic observation and its image analysis. The experimental results revealed that the melting and oxidation behavior were influenced by reinforcing configuration and electric resistivity of CFRTP laminates. The melting area of both CFRTP laminates tends to increase with increasing the applied voltage and conducting time. It was found that the insertion of PPS films in melting interface was required in order to prevent the edge effect and non-uniform profile shapes of the melting area. It was also confirmed that woven CF/PPS laminates could be melted at low applied voltage.
Carbon fiber reinforced plastics (CFRP) have high specific rigidity and high specific strength. But it is poor in vibration damping. In this research, in order to improve the damping properties of CFRP, the damping behavior was investigated by dynamic mechanical analysis (DMA).The tan δ and E were calculated by the RKU equations. As a result, CFRP/polymer laminates were found to exhibit a high damping property by placing the 90 ° layers in the vicinity of core layer. A new approach of cutting part of damping sheet was proposed and both modulus and damping property could be obtained by adjusting the ratio of cutting part, which is effective way in designing optimum damping materials. It was found for CFRP materials RKU formula should be modified with the consideration of value of tan δ in CFRP layer, which will provide a better prediction for damping property.
In this study, we propose a FE model for dry fabric forming simulation that can express the tension dependent shear behavior in order to predict the wrinkles, one of the major forming defects. Automakers are gradually using more carbon fiber reinforced plastic (CFRP) in mass production cars, because the development of resin transfer molding (RTM) have reduced its cycle time to less than 10 minutes. Finite element analysis (FEA) is essential to the vehicle design process, so numerical simulation of CFRP is strongly desired today. Forming simulation is especially important, because the performance of the final composite part strongly depends on changes in fiber orientation during the preforming. Moreover wrinkle is one of the major defects in preforming. RTM usually involves fabric reinforcement. During forming of fabric, large in-plane shear deformations typically occur. The reason for this is that the shear resistance is very low at the initial stage, because the deformation is governed by yarn contact friction at the cross-sections. Accurately expressing the in-plane shear behavior of fabric is very important for accurate forming simulation. In most simulation models the shear resistance of fabric is assumed to be independent from the tension along the yarn. However, meso-model predictions of the picture frame and bias-extension tests suggest this to be an invalid assumption. In this study, a micromechanical model that introduces the stress component due to the yarn rotational friction is adapted to the dry fabric forming simulation. In other words, this can express the shear behavior that depends on the tensions in the yarns. The results using this micromechanical model are in good agreement with the meso-model results in the various boundary conditions.
Estimation method of fatigue life for textile composites was proposed. Because textile composites have a many design parameters such as fiber type, resin type, architecture of reinforced fibers, volume fraction of fiber and fiber orientation, etc., it is difficult to obtain enough fatigue test data for all combinations by experimental procedures. In the proposed method, textile composites were treated as heterogeneous bodies with anisotropy for fiber bundles and isotropy for matrix, respectively. The stress distribution under cyclic loading was evaluated by FEM. On the other hand, each element of FE model was considered as unidirectional materials and their properties under cyclic loading are estimated from fatigue test. The proposed method was applied to plain woven CFRP. It was confirmed that the proposed method is applicable to estimation of fatigue life of textile composites.
This study proposes an effective technique to improve the flexural strength and flexural modulus of the stampable sheet fabricated with bamboo fibers. Non-woven cloth fabricated with bamboo fibers and PP (polypropylene) slivers were prepared by conventional carding method. The non-woven cloth was pressed on a heat press machine to make the stampable sheet after soaking in a PVA(Poly Vinyl Alcohol) water solution and then they were dried in an electric oven (PVA treatment). Specific bending strength and specific elastic modulus of the stampable sheets were determined by three point bending tests. The interfacial strength between treated bamboo fiber and PP were also measured by the pull-out test, after the tensile property of treated bamboo fiber was investigated.Results of three point bending tests showed, at first, that 80.1% of improvement in specific strength of was observed, when the stampable sheet was fabricated with the modified bamboo fibers appropriately treated by the PVA solution. It was suggested that the PVA worked as the adhesive between bamboo fibers and PP, in which interfacial failure was prevented by the PVA treatment, while debonding was observed in original stampable sheet with untreated bamboo fibers in this study. By the PVA treatment, 55.6% of improvement in specific flexural modulus of the stampable sheet was also obtained. It was also suggested that the enhancement of flexural modulus was explained by the improvement of observed elastic modulus around the connected bamboo fibers so that elastic deformation of adhesive connections constructing bamboo fibers network was prevented, if the bamboo fibers were treated with PVA solution.
Cu-2.0wt%Ni-0.5wt%Si, Cu-1.4wt%Ni-0.6wt%Co-0.5wt%Si (0.6%Co) and Cu-1.0wt%Ni-1.0wt%Co-0.5wt%Si (1.0%Co) alloys produced by combining cold rolling to a 25% and a 90% reduction with aging treatment are employed to investigate the effects of Co on the strength and microstructure of Cu-Ni-Co-Si alloys. Aging the 0.6%Co and 1.0%Co alloys at 525, 425 and 325℃ produces orthorhombic (Ni, Co)2Si precipitates that have the same crystal system as Ni2Si precipitates formed in the 0%Co alloy. The larger the amount of Co in the three alloys is, the higher the dislocation density in the alloys peak-aged and rolled to a 25% and a 90% reduction is. The amounts of deformation twins observed in the 0.6%Co and 1.0%Co alloys peak-aged at 525℃ and rolled to a 90% reduction are much larger than that observed in the 0%Co alloy peak-aged at 525℃ and rolled to a 90% reduction. The strength and electrical conductivity of the three alloys initially aged at 525℃, rolled to a 25% reduction and re-aged at 425℃ (A25RA), or aged at 525℃, rolled to a 90% reduction and re-aged at 325℃ (A90RA) becomes higher as the Co content increases. The increase in strength with increasing the Co content is attributed to decrease in the inter-precipitate spacing and increase in the dislocation density for the A25RA alloys, and increase in the amount of deformation twins in addition to decrease in the inter-precipitate spacing and increase in the dislocation density for the A90RA alloys.
As known as typical texture material with coarse grain, weld metal or its vicinity meets difficulties in residual stress measurement especially using sin2ψ method with conventional zero or one-dimensional X-ray diffraction. In this study a two-dimensional X-ray diffraction system based on cosa method is developed for in-service residual stress measurement of weld metal in structural components. Validity of residual stress measurement using this system is verified by several confirming tests including nickel-based weld metal. Positioning jig is designed and fabricated for welds on the shroud support plate of boiling water reactor (BWR). Setup test on the mock-up of BWR bottom area shows the possibility of in-service measurement using this system.