Effect of Large Hydrostatic Pressures on the Torsional Fatigue Strength of two Steels

This paper describes tests in which two alloy steels were subjected to reversed torsion at atmospheric or high ambient pressure. It is shown that if the specimens are protected, superimposed fluid pressures increase the fatigue limits of both steels. For instance a pressure of 25 ton/in² raises the nominal fatigue limit of a 2 1/2 per cent nickel-chromiummolybdenum (En 25) steel by about 46 per cent. It is concluded tentatively that a superimposed hydrostatic pressure improves fatigue strength by introducing a compressive stress on planes of maximum alternating shear stress.