NIMS fatigue data sheet on low- and high-cycle fatigue properties of A2017-T4 (Al-4.0Cu-0.6Mg) aluminium alloy

The new fatigue data sheet, No. 133, discloses low- and high-cycle fatigue properties of A2017-T4 aluminium alloys. Two types of low-cycle fatigue tests were conducted under strain-controlled conditions. One comprised incremental step tests to clarify cyclic stress-strain curves. The other comprised constant- strain amplitude tests to clarify the fatigue lives. The aluminium alloys revealed strong cyclic hardening that resulted in very high cycle yield stresses. The cyclic yield stresses were higher than those of titanium alloys and steels. Constant-strain amplitude tests showed plastic strain amplitudes to be smaller in most cases than elastic strain amplitudes. These appeared to be attributable to the small elongation, low elastic modulus and strong cyclic hardening of the aluminium alloys. Three heats of A2017-T4 revealed equivalent fatigue lives when their fatigue strengths were evaluated by strain amplitude. Evaluation by stress amplitude, in contrast, resulted in differences between heats, likely caused by the effects of cyclic yield stress. The high-cycle fatigue tests up to 108 cycles were uniaxial and carried out under load-controlled conditions. Many specimens fractured at over 107 cycles, so fatigue limits were not confirmed. The high-cycle fatigue strengths were proportional to the tensile strengths. The 107-cycle fatigue strengths were close to those of austenitic stainless steels and normalized carbon steels, while the 108-cycle fatigue strengths were lower. In short, the fatigue strengths deceased at over 107 cycles, showing the need for gigacycle fatigue tests. These will be described in the next issue.