Study on Fatigue of Metals by Measurements of Internal Friction

Abstract

Changes in internal friction during the course of fatigue and by annealing after fatigue were measured at the same amplitudes as in the fatigue tests in mild steel, electrolytic iron and OFHC copper. The main cause of the measured internal friction was the static hysteresis loss. The losses generally increased with increasing number of fatigue cycles except in the early stage of fatigue. The increasing losses began to recover by annealing at 215°C for more than 45 min both in mild steel and electrolytic iron and by annealing at about 15°C for more than 1 min in copper. The decreases of the losses in mild steel and electrolytic iron by annealing were probably due to the precipitation of cementite and in copper probably due to the clustering or the formation of secondary defects of vacancies produced by fatigue which must impede the motion of dislocations. It was also estimated that in fatigue tests at 2000 c/min the effects of the precipitation of cementite and of the clustering of vacancies on fatigue strength would become noticeable at about 350°C in mild steel and iron and at about 90°C in copper respectively.