1996 年 45 巻 1 号 p. 48-54
Crack initiation and growth in polycarbonate specimens under lubricated rolling contact loading were observed with a monitor microscope, and their failure mechanisms were investigated. When a fatigue crack initiated at the contact surface, the crack tip lay in the plane of the maximum shear stress in the first stage of crack growth. Next it turned the direction perpendicular to the maximum principal stress direction. In this case, pitting type failure occurred due to the crack extension. Butterfly type failure occurred after secondary crack extension due to the concentration of shear stress around the cracked region. The shear mode growth of cracks was observed when the cracks initiated at the side surface of the specimen. In this case, flaking type failure occurred. It was found that the failure mechanism of the present specimen correlated well with the crack extension mode and different mechanisms were observed in the formation of pitting, flaking and butterfly patterns.