On the Change of the Internal Friction Due to the Repeated Stresses

Abstract

During the rotating-bending fatigue tests, the logarithmic decrements of 0.1% carbon steel (cold drawn wire rod, 3.25 mm in diameter) are measured by the damping method in a frequency range from 56 to 2 250 cps., and the mechanism of fatigue fracture is studied from the change of the internal frictions. It is concluded that the intercrystalline strain gradient induced within the material as a result of repeated stresses plays an important role and the imperfection of the structure plays the secondary role in the fatigue failure, which sets in as microscopical cracks within the crystals in the earlier stage of the repetition of stresses and propagates itself to cause the fracture of the whole material.