Development of Thermoplastic Press Sheet with In-Plane Randomly Oriented and Dispersed Carbon Mono-Fibers and Evaluation of the Mechanical Property

We have developed a novel stampable sheet composed of discontinuous carbon mono-fibers and thermoplastic resin for press molding of composite materials. This sheet enables in-plane random orientation and dispersion of carbon fibers in composites. Therefore, complexly shaped products, such as rib structures, are easily fabricated. Moreover, composites having superior mechanical properties can be obtained because the fiber length in composite is easily controlled to be long. This study addressed the effect of fiber length on strength and fracture modes of composites made of the sheet, using tensile tests and micromechanical analyses. To investigate the influential damage for the fracture mode, our analysis utilized Duva-Curtin model for fiber breakage. We incorporated this damage model into an equivalent inclusion model combined with the Mori-Tanaka theory to predict the tensile strength of the composites. The predicted results agreed well with those of the experiments when the fiber length and orientation in the composites were appropriately considered. Our analyses also indicated that 3 mm as the lower-limit fiber length in the composite, below which the damage mode is no longer dominated by fiber breakage and superior strength of the composites cannot be obtained.