高静水圧下のアルミニウム合金の低繰返し数疲れ

Abstract

In order to investigate the effect of hydrostatic pressure on the low-cycle fatigue strength, a push-pull fatigue testing machine under high pressure was developed. Using this machine, strain-controlled low-cycle fatigue tests were carried out on 5005 aluminum alloy specimens under several different pressures.The fatigue test results under high pressures were found to be expressed by linear relations on the log-log scale between the strain range and number of cycles to failure. Increasing the pressure from 0 to 3900 kg/cm2 slightly increased the fatigue life of this material, although this increase of fatigue life was considerably less than that expected from the Manson-Coffin relation through the pressure dependence of fracture ductility. Suppression of the tensile stress component of the applied stress by pressure did not yield any discrete change in fatigue life. This may be interpreted that under high strain amplitude conditions the strain range is a primary factor determining fatigue failure including fatigue crack propagation. Some micrographic studies revealed little effect of pressure on the surface slip process under cyclic strain and also on the appearance of the final fracture surface. Coating of the specimen had little effect on the fatigue life.