Carbon fiber tows are generally used for the reinforcement of plastics. Recently, we have developed a method in which tow can be efficiently spread without causing any fiber damage (FUKUI method). By using this method, we prepared thin laminas about 0.05 mm in thickness, and produced quasi-isotropic laminates by stacking these laminas. Furthermore, we obtained the laminas having an arbitrary thickness by stacking the laminas with the same unidirectional prepregs. In this work, the effects of the lamina thickness on the first ply failure occurred in multidirectionally laminated composites have been studied. Tensile tests were performed on the samples and also acoustic emission was monitored during the tests. It is found that the initial failure stress increases with decreasing lamina thickness. This result can be predicted by Kageyama's study.
