Pitting of Steel Under Varying Speeds and Combined Stresses

A new loader is described for pitting research. It consists of a ball in a cylinder. Behind the ball is high-pressure oil which forces it against the moving counterface, which in its turn causes the ball to spin, and so remain centered in the cylinder. In the first part of the paper the effect of speed on pitting is studied using this loader. The results are correlated by a mathematical treatment of Way’s hydraulic crack-propagation hypothesis. The theory shows that high viscosity and compressibility and short transit times increase pitting life. Semiquantitative agreement is found between the new pitting theory and experiment. In the second part the action of combined stresses on pitting is investigated. The ball is loaded against a shaft mounted in a rotating-bending fatigue machine. It is found that a relatively small tensile bending stress reduces pitting life dramatically, whereas a small compressive bending stress completely inhibits pitting.