CFRP composite plate structures have been generally known as that those have high specific mechanical properties. The CFRP composite plate, therefore, has been widely applied to many kinds of aircraft structures. The composite plate structures, however, have a week point at interlamina strength. Since a delamination resistance of its plate is very low, delaminations easily yield by a low velocity impact loading or fatigue loading. For this reason, a smart structure to detect a delamination is desired now. In this study, therefore, an applicability of an electrical potential method to detect a delamination was examined experimentally from a stand point of a sensor for a smart structure. Effects of prepreg thickness, kind of electric current of electrical resistance bridge, loading mode and stacking sequence were all experimentally researched by using T 300/Epoxy. Mode I and II types of tests were conducted and the electrical resistance changes were measured by the electrical resistance bridge circuit. As a result, the followings were obtained. (1) In the case that there are many interlaminae by using thin prepreg sheet, the electrical resistance change is smaller than that of thick one because the electrical resistance to the plate thickness becomes large. (2) The AC is better for an electrical resistance bridge circuit than DC because it gave more stable results than those by DC. (3) Though the delamination crack surfaces contact with each other in the mode II tests. The electrical resistance change could be measured by the AC electrical resistance bridge method. (4) In the actual composite, plates, the nonlinear relations between the delamination crack growth and the electrical resistance of the specimen were obtained due to the delamination crack plane transition.

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Internal stresses in three-dimensional fabric composites are reported to be remarkably higher than those in usual laminate composites. Therefore three-dimensional fabric resin matrix composites produced by general forming method have many cracks in the matrix and along the interface between reinforcement and matrix. In this paper, the effect of mixing fillers in the matrix resin on the internal stress in the three-dimensional fabric composites was examined aiming to develop prevention method of the cracks along the interface and in the matrix. Among commercially available particulates, quarts, glassy carbon, and silicone rubber were chosen as the filler for the matrix resin. The internal normal stress on the interface was calculated from the experimentally obtained values of thermal expansion coefficient and Young's modulus of the filler-mixed resin. It was found that quartz and glassy carbon particulates were of little effects but dispersing silicone rubber particulate was quite effective to lower the internal stress in three-dimensional composites. It was also found that the silicone rubber particulates were turned into microvoids in this composite. Thus the effect of mixing silicone rubber particulates is actually equal to that of the microvoids.

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Fracture toughness of polypropylene (PP) and its composites has been investigated in relations to the crystallinity of PP, to the glass bead filling and to the surface treatment of glass bead. Raw materials used for the matrix were the high crystalline PP and the general purpose PP. The crystallinity of PP was controlled by the cooling conditions after the hot press molding of PP. The glass beads were treated with various silane coupling agents. The fracture toughness of PP and its composites, measured by the compact tension type test pieces, has decreased remarkably with the increase of the crystallinity of PP. In the case where the crystallinity of PP is low (<49%), the fracture toughness has increased by the filling of the glass beads, and it has further increased by the surface treatment of glass beads. The wettability (the critical surface tension) of the glass plates treated with various coupling agents has shown good correlation with the fracture toughness for the low crystalline composites.

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In the previous papers, the authors have studied strength deterioration of injection-molded short glass fiber reinforced polyamide 6 due to the addition of a slight amount of titanium dioxide on the basis of micromechanics. This paper is concerned with the influences of quantities and kinds of inorganic addition agents on the strength deterioration. It was found that the strength deterioration depends on the hardness of inorganic addition agent and scarcely depends on the amount. The strength reduces as the hardness of inorganic addition agent becomes higher. Finally the strength deterioration of unnotched composites and maximum load of the notched ones were numerically predicted. Good agreement was found between the predicted and experimental results.

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