Strain-controlled tests for determining the changes in the fatigue parameters of materials

We present the results of fatigue testing of cyclically hardened 2017(A)-T4 aluminum alloy (AlCu4 Mg Si) for five levels of cyclic strains. The cyclic instability of this material hardened under variable cyclic loads leads to the variations of the coefficients of fatigue characteristics of the Manson-Coffin-Basquin curve. The analysis of these changes in the process of evaluation of the fatigue strength of materials enables us to improve the values of this quantity for cyclically unstable materials. We propose a model for the evaluation of the fatigue strength of materials under random loading and, in particular, for the variable characteristics and coefficients of fatigue strength and plasticity.