On the effect of stress intensity factor in evaluating the fatigue crack growth rate of aluminum alloy under the influence of compressive stress cycles

To date, most of the studies conducted on fatigue life estimation of structural components have focused on the Constant Amplitude Loading (CAL) scenarios. However, very few structures in the real world experience such a loading condition, and most structural components undergo a Variable Amplitude Loading (VAL) during their service life. It is also observed that most of the available fatigue crack growth (FCG) models ignore the influence of the compressive stresses, despite the fact that recent studies have highlighted the detrimental effect of compressive stress cycles (CSCs) on the FCG of materials. In this paper, a VAL stress–time history is used to study the fatigue response of 6061-T651 aluminum alloy, with a focus on the compressive portion of the stress time history. An experimental investigation is conducted to assess the influence VAL, in particular, the influence of the CSC on FCG of the material. In the tests, the tensile portion of the stress–time history was kept unchanged, while the compressive portion of the stress–time history were varied by various scaling factors. The experimental results demonstrate that the compressive stress portion of the applied load has a significant influence on the overall fatigue life of the material. It is observed that even introducing a few number of small CSC into the stress–time history can significantly decrease the fatigue life of the material. In addition, the influence of the CSC is also examined by means of a microscopic evaluation of crack surfaces’ roughness.