Die cushion motion has been applied to the forming of ribs of discontinuous carbon-fiber composites with panel forming of continuous carbon fiber composites during press forming. This method has the advantage that only a small die cushion load is necessary to form ribs and the length of discontinuous carbon fiber is not damaged during forming. Basic equipment to form a 100-mm-square and 20-mm-high cup with 4-mm-thick cross ribs was designed and fabricated. As the billet material, a flat plate made of randomly oriented thermoplastic discontinuous carbon fiber tapes of 30 mm length and 10 mm width was prepared. Extrusion of the billet to the rib made the fibers flow in the longitudinal rib direction. By using a billet push pin, whose head has a groove for the rib, strong bending strength of the panel was achieved. By pushing the billet material to the rear surface of the panel, fiber flow from the rib to the panel rear surface was formed at the junction, and strong joining strength between the rib and the panel was obtained.
In this study, the degradation of the strength of press-formed hemispheres of thermoplastic matrix composite (CFRTP) was investigated considering the residual stress in fibers generated during the forming process. CFRTP sheets reinforced with woven carbon fiber fabric were stamped into hemispheres under various conditions of die temperature and blank holding force. The strength of formed hemispheres was evaluated by the internal pressure test. Residual stress in fibers around the fracture origin was directly measured by the micro-Raman spectroscopy and then its relation with the internal pressure strength was examined. As a result, die temperature was found to have negligible effect on the fracture pressure. On the other hand, blank holding force strongly influenced the internal pressure strength. The variation in strength was well correlated with fiber residual stress, which varied little with die temperature but changed significantly with blank holding force. It was well explained that the decrease in strength could be mostly due to fiber residual stress. Fiber residual stress differed with location, resulting in a local distribution of strength in the press-formed composites.
The purpose of this study was to investigate the usefulness of dissimilar joining utilizing the property of expansion of the carbon fiber-reinforced thermo plastics (CFRTP) plate near the melting temperature of the matrix resin in the thickness direction. We developed a method to obtain joining strength by generating a force to push an Al piece from out of a groove potion by heating it provided with straight and tapered groove to an arbitrary temperature and then inserting CFRTP and expanding it. Experimental results and joining strength were evaluated. In addition, to confirm the relationship between the thermal expansion of CFRTP and the joining strength, the increase in plate thickness was examined when a CFRTP plate was sandwiched between two previously heated Al plates. Furthermore, to compare joining strength, the same test piece was adhered to the Al piece with epoxy adhesive and the joining strength was evaluated. As a result, a relationship between expansion due to the heating of CFRTP and joining strength was confirmed. Furthermore, by tapering the groove portion of the Al piece, almost the same joining strength as that when using adhesive was obtained.