In ceramics matrix composites (CMCs), the fiber/matrix interfacial sliding is the main toughening mechanism. In the present study, the interfacial sliding problem was formulated by the constraint conditional finite element method (CC-FEM). In this formulation, the equality of nodal displacements at the interface and the equilibrium of contact forces are assumed as constraint conditions, in which Coulomb’s law of friction is taken into account. As a distinguished advantage, the numerical solutions can be obtained by only one calculation without iterative algorism. In the previous papers, we treated the case such that the fiber in a CMC was oriented along the loading direction. But, in actual CMCs, the fibers are not necessarily oriented along the loading direction, and the fiber diameter also fluctuates along the axis. In this study, thus, the off-axial interfacial sliding problem was formulated, and the validity of CC-FEM was discussed by comparing with ANSYS. The results show that, in the both cases of on- and off-axial interfacial sliding, the resultant stress distributions of the fiber and matrix agreed well with those of ANSYS. As compared to the case of on-axial interfacial sliding, the matrix stress recovered more steeply because of the higher equivalent frictional coefficient.
One of authors in this paper developed glass fabrics reinforced thermoplastics (GFRTP) and carbon fabrics reinforced thermoplastics (CFRTP) using in-situ polymerizable ε-caprolactam as matrix. They had no voids and unfilled resin parts because the ε-caprolactam had very low viscosity before polymerization. Furthermore, their FRTPs not only exhibited superior mechanical properties, but also were suitable for high-speed molding, namely within a few minute process time because they could be released from the mold without a cooling process. In this paper, in order to apply the FRTPs for the wider area, the carbon/glass hybrid fabrics reinforced thermoplastics (HFRTP) using the in-situ polymerizable polyamide 6 as matrix was fabricated, and their mechanical properties were evaluated by bending test, izod impact, static compressive and tensile tests. Moreover, hybrid fabrics reinforced plastics (HFRP) was fabricated using same carbon/glass hybrid fabrics as the HFRTP and fast curable epoxy resin.
Carbon fiber reinforced thermoplastics (CFRTP) have great potential about high-cycle molding in one minute. However, the relationship between cost reduction and well-impregnated composite materials for automotive parts is trade-off because thermoplastic resins have high viscosity and difficulty for impregnation into reinforcement fibers. So an effective quantification on impregnation of CFRTP is required for mass production of automotive parts. Non-destructive quantification of void fraction of CFRTP with soft X-ray transmittance were investigated. We measured X-ray transmittance of CF/PP plate with 3 different void content. As a result, the attenuation coefficient of X-ray had highly linear correlation with the density, which can be used to calculate void fraction of composite. In conclusion, non-destructive measurement by soft X-ray can be applied for the quality management of mass production of automotive parts because the distribution of void content in parts can be measured.
A new technique using Lamb wave is proposed to detect uncured region in GFRP laminates nondestructively. Polymer based composites play an increasingly important role in the field of civil engineering in recent years. For example, laminated sheets consisting of thermoplastic layer, organic fabric sheets and SMC (sheet molding compound) are used to rehabilitate aged sewerage pipes. The cylindrical laminate is inserted in the pipe, and is inflated and cured by steam blowing to create close-fit pipe. This CIPP (cured in place pipe) is one of several trenchless rehabilitation methods to repair aged pipes. In this study, ultrasonic Lamb wave is applied to the detection of uncured region in a laminated composite plate. Oblique incidence method in which ultrasonic waves are launched by the transducer inclined at a selected angle is applied to excite specific mode of Lamb waves in the laminate. Wheel type probes are used to improve inspection efficiency. Beside wave attenuation, AU parameters which are derived from power spectrum of a broadband signal are introduced. It is found that application of AU parameters leads to the improvement of the detectability of uncured region.