Effects of Surface and Internal Structure Changes on Fatigue Properties of Copper : Experiments on Fatigue Mechanism, 1st Report

Abstract

Two effects acting on fatigue properties of copper were investigated; the surface damage such as intrusion-extrusion and the internal structure induced. The former effect was examined by repetition of electro-polishing the surface layer and cyclic stressing. The fatigue life can be prolonged unexpectedly by such processes, but the damaged layer increases in thickness at the later stages of operation and eventually a fracture occurs. If the amount of polish is increased at these stages so as to remove perfectly this layer, an infinite extension of the life seems to be expected. In specimens fractured, the more cells and dipoles were observed than in the ordinary fatigued specimens. These structures seem to play a part in increasing the crack growth rate. An attempt has been made to present a dislocation model for the crack growth at the 1st stage of fatigue, in which dipole dislocations play an important role.