The fiber breakage behavior of unidirectional CF/epoxy composite material was estimated taking into account the stress concentration in the adjacent fibers resulting from the matrix crack around fiber breakages. In behavior analysis of the adjacent fiber breakage in the double-fibers fragmentation tests, the simulation using the spring elements model taking into account the stress concentration in the fiber surface corresponds well with the experimental results. In addition to the introduction of the stress concentration factor, it is essential for employing the bimodal Weibull distribution which is narrow strength distribution in high strength region in order to explain the experimental behavior of the double-fibers fragmentation tests. Furthermore, the predicted tensile strength for the unidirectional CF/epoxy composite material taking into account the stress concentration to the adjacent fibers resulting from the matrix crack around fiber breakages, using the spring elements model agreed well with the experimental results. This suggests that there is considerable contribution for improving tensile strength of composites, for the suppression of stress concentration in the fiber surface.
This paper presents analytical solutions to eddy current distribution in carbon fiber-reinforced plastics induced by line current. Derived solutions show that eddy current distribution in unidirectional carbon fiber composite is dependent only on electrical conductivity in the drive current direction when the drive current is directed in the fiber direction or the transverse direction. Moreover, according to the derived analytical solution, skin depth of eddy current depends not only on frequency of drive current but on lift-off and width of the drive current unlike general expression of skin depth. Finally, we discuss improvement of sensitivity of eddy current conductivity sensor using analytical solutions. It is found that analytical solutions can clearly divide effects of magnetic field from drive current and that from eddy current. Sensitivity of eddy current sensor can be improved by 10 times placing pickup coil at region where the effect of magnetic field from eddy current is large.
For the configuration of the CFRP face plates/foamed plastic core sandwich panel joint, a tapered end-closure type joint is selected and studied. In this type of joint, the sandwich panel is tapered to form the solid laminate of two face plates near the joint portion and two panels to be joined are mechanically fastened at the solid laminate portions with a splice plate. This type of joint could be suitable for the aircraft panel joint configuration, because a flat surface can be obtained at the joint portion, which is advantageous in an aerodynamic point of view. However, in a previous study, it was reported on the results of tensile strength test that the delamination crack initiating from tapered core end and propagating through the interface between two face plates was observed as an initial failure mode at much lower tensile load compared to the final failure load. In this study, the angle of tapered panel portion is focused on and the initial failure suppression effect caused by the change of taper angle is investigated through experiment and numerical analysis. And it is found that the smaller taper angle is preferred to suppress the initial failure.