日本複合材料学会誌

To investigate void formation during resin transfer molding (RTM) processes, we developed a numerical code of a multiphase fluid model that employs Navier-Stokes equation including the interfacial tension term and Cahn-Hilliard equation for capturing the resin-air interface. We performed preliminary numerical simulations of microscale resin-air flow around a regular-lattice array of four single filaments. From the analysis, we found that (1) Laplace pressure arisen from the finite curvature of the resin-air interface could drive a capillary-driven flow penetrating into the gap between the two filaments located in longitudinal direction; (2) there was another dual time scale even at the microscale on the determination of flow patters: one was caused by the main flow, and the other by capillary driven transverse flow; (3) voids could be formed when the time scale of the main flow was shorter than that of capillary flow; (4) two modes of void formations were revealed numerically: longitudinal gaps fully capped by the resin-air interface leading to the void formation under a high interfacial tension coefficient; and a small bubble left at the back-step of the filament under a relatively weak interfacial tension coefficient.

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Progressive crushing tests of unidirectionally laminated carbon fiber reinforced plastic (CFRP) rectangular plate were carried out to reveal its continuous fracture behavior and energy absorption. A special test fixture was developed for the test and fracture process of the CFRP was observed from its side section. Three types of trigger geometries, i.e. chamfer, steeple and V-shape trigger, were machined on each specimen. Film embedded V-shape trigger was also prepared to investigate the effect of initial cracks on energy absorption. The initial fracture behavior strongly affected the ensuing stable fracture process. It was clarified that V-shape trigger specimen was robust over the variation of gage length (unsupported length) as compared to chamfer and steeple trigger specimen which showed smaller energy absorption with longer gage length. A column-like part, which was called pillar in this paper, was observed between fronds under crushing. The fracture was much severe at pillar section than fronds section. Fiber fractures were observed periodically at 50-100 μm length in the pillar section, which coincides with the length of kink band in ultimate compressive failures of CFRP. It was revealed that the thickness of pillar was dominant factor on energy absorption of unidirectional CFRP.

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