Two types of tensile specimens of short-glass-fiber reinforced PPS (polyphenylene sulfide) (SGFRP) were cut from the surface layer of injection molded plates. They were 0° specimens with fibers predominantly oriented in the loading direction and 90° specimens with fibers perpendicular to the loading direction. During loading and unloading, the change of the matrix phase stress in SGFRP measured by the synchrotron X-ray method showed a good agreement to the value computed by micromechanics considering fiber orientation distribution. The matrix phase stress in the loading direction at tensile fracture of 0° and 90° specimens were about the same, although the tensile strength of the former is much higher than the latter. The matrix phase stress of SGFRP at fracture was nearly half of the fracture stress of PPS specimens without reinforcement. The reduction of fracture stress of PPS matrix comes from the stress concentration due to fibers. The fatigue life of smooth specimens of SGFRP was also controlled by the matrix stress increased by an amount of stress concentration factor. When the fatigue life is correlated to the matrix equivalent stress, S-N diagrams of 0° and 90° specimens including PPS specimens showed an almost identical relationship. The same factor of stress concentration applicable to tensile and to fatigue fracture may provide a physical basis for good correlation between the fatigue strength and the tensile strength of SGFRP.
