The mechanochemical reactions of three kinds of FRP (Fiber Reinforced Plastic) were investigated at room temperature up to 50kbar static pressure by using a self-made high pressure apparatus capable of simultaneous shear deformation. All shearing curves showed such a characteristic variation that the shear-strength smoothly decreased after the gradual increase of it, and the higher the static pressure was applied, the clearer the tendency was observed. Although FRP is one of the most stable organic composite materials under these conditions, such a variation of the shear-strength is probably the demerit for practical use. The results of ESR studies together with the above shearing experiment suggest that the mechanochemical reaction of FRP proceeds mainly in the matrix area, and the fracture of the filament fiber itself scarcely occurs.
