Fatigue of aluminum by uniaxially repeated tensile load

Abstract

Measurements of deformation and internal friction and optical microscopic observation were made on commercial pure aluminum specimens when they were under various uniaxially repeated tensile loads.The uniaxially repeated tensile load was cyclically given by a loading machine with an eccentric cam. It was given by pulling the spring to the stroke of 10mm and various loads were given by the exchange of the spring.The relation between amplitude and repeated number to rupture was nearly identical with the S-N relation in ordinary push-pull fatigue test. Two types of rupture were observed under the uniaxial repeated tensile stress conditions. One was a ductile rupture which gave a large local contraction, but the other would be a fatigue rupture which did not give a so large local contraction. The former ductile rupture occurred under the conditions of higher stress and its total elongation attained to about 5060%. Whereas, the latter fatigue rupture occurred under the conditions of lower stress and its total elongation attained to about 20%. Slip band striations were sharpl yproduced under lower stress conditions and clear caterpillar patterns to be characterized by fatigue rupture also appeared on the fracture. They were much different from those produced in the structure under the conditions of higher stress or tensile test.The change in amplitude-independent internal friction with total plastic strain under various stress conditions was plainly increased with the increase of total plastic strain.