There are a lot of schemes for predicting long-term durability of composite materials. As the scheme becomes complicated, the prediction would be precise whereas the prediction needs more numbers of constants. If many of parameters are needed, in fact there is a case it is difficult to predict that because the acquaintance of all of them is almost impossible. A numerous number of constant hinders us to apply the scheme ; but when the number of constant is smaller, more of us can apply the model, i.e. easy to use. The simultaneous fiber failure (SFF) model presented by Koyanagi et al only needs small number of constants ; about ten constants are needed for predicting long-term durability precisely. The number might be however still much compared with kinetic crack growth (KCG) theory presented by Christensen, which does not model actual composite failure mechanism. The consistency between SFF and KCG is discussed in this paper. If KCG works well, KCG is better to apply for predicting longterm durability because necessary constants are less. This paper introduces the two models and then compares them.

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In this study, immersion tests on poly (L-lactic acid) (PLLA)and their composite with β-tricalcium phosphate(β-TCP) to phosphate buffered solution(PBS) at 37℃ was carried out to investigate the effect of immersion in PBS on tensile mechanical properties. A simple phenomenological model to predict tensile elastic properties of hydrolyzed biodegradable polymer and their composites was also constructed by assuming voids generation in the hydrolyzed sites of the polymer. The analytical results for number averaged molecular weight are in good agreements with experimental results in any specimens, and it seems to be the evidence of autocatalytic hydrolysis of PLLA. Furthermore, the model shows that the hydrolytic degradation rate constant decreases with β-TCP contents. It means that β-TCP particle has inhibitive effect on hydrolytic degradation of PLLA. Although the predicted value has large error on the later scheme of hydrolysis, the model describes tensile elastic modulus trend of degraded PLLA and β-TCP/PLLA composites reasonably.

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In this study, dispersed carbon nanofibers (CNFs) in an uncured epoxy resin have been aligned by applying traveling electric field in a multiple electrode. In the multiple electrode, two ctenoid-shape electrodes were symmetrically located. The dispersed CNFs in the long and narrow space between the ctenoid-shape electrodes were aligned to the longitudinal direction of the space. Same voltages were applied to opposite electrode pairs. The applied voltages were successively and cyclically switched to the longitudinal direction. In this way, the traveling electric field was applied to the CNFs/uncured epoxy resin suspension. Before the experiment, the shape and arrangement of the electrodes in the multiple electrode and the voltage application schedule to the electrode pairs were designed. Static electric fields at steps in the voltage application schedule were calculated by using 2D FEM. The obtained static electric fields were substituted into the predictive model proposed by one of the authors. The model gives aligned CNFs direction and magnitude of the moment applied to the CNFs by applying traveling electric field. Furthermore, influences on the CNFs alignment of the applied voltages and the arrangement of the electrodes were clarified.

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Carbon fiber reinforced plastic(CFRP)has the superior properties such as specific strength and stiffness compared with conventional metallic materials. CFRP is usually used as a laminated structure, and CFRP has also electric conductivity. When a dielectric layer is inserted between the CFRP plies, we can use the CFRP structure as a capacitor by utilizing CFRP as electrodes. This is a kind of multifunctional composites, and is called CFRP structural capacitor. CFRP structural capacitor has the potential of substituting some batteries or electric double layer capacitors(EDLC).The weight and space of batteries can be reduced and the cost is also reduced because batteries are usually very much expensive. For practical application, we have to study both mechanical and electrical properties. In the present paper, electrical properties of the structural capacitor is investigated. The conductivity of the CFRP is lower compared with conventional metallic materials. This indicates that the internal electrical resistance of the capacitor can be crucial to CFRP structural capacitor. The internal electrical resistance is calculated using electrical current analysis of the CFRP structural capacitor. To reduce the internal resistance by changing many parameters. As a result, CFRP structural capacitors should be connected in parallel, and matrix like electrodes should be used to reduce the internal resistance.

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CFRP is an electrically anisotropic material composed of conductive carbon fibers and insulator resins. In addition, CFRP has various applications such as unidirectional CFRP and woven-fabric CFRP. Although electrical conductivity of typical CFRP laminates of thickness direction has been measured, an interlayer conductivity between unidirectional CFRP and woven-fabric CFRP has not been measured. In the present study, the authors propose an identification method for the contact resistance of an interlayer between thin unidirectional CFRP and thin woven-fabric CFRP experimentally and analytically. In the measurement, electrical current is applied between two electrodes diagonally placed on the surface of unidirectional CFRP so that the bottom woven-fabric CFRP becomes a conducting path. The electrical potential in the middle area of the specimen is measured on the four center-electrodes. In FEM analysis, a virtual layer demonstrating for only contact resistance is inserted between two kinds of carbon fiber laminates and the electrical conductivity of thickness direction δZ that coincides with the measurement result is searched by trial and error. As a result, a contact resistance is measured between two different plies and the study finds that electrical conductivity of thickness direction is 1/10 times as small as one of transverse direction of unidirectional CFRP. Moreover, the authors calculate electrical conductivities of thickness direction of the interlayer between only unidirectional CFRPs or woven-fabric CFRPs analytically and find that contact resistance between unidirectional CFRP and woven-fabric CFRP is almost equal to one of unidirectional CFRPs.

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