Page 42 - Міністерство освіти і науки України

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of block II, and decreases at the start and end of block I at the stress ratio R = 0.09 – 0.13.
In contrast to this, the dissipation energy is proportional to the number of loading cycles at
the start and end of block I at stress ratio R = 0.33–0.51.
The elastic strain energy density, as a criterion of pseudoelastic nitinol fatigue failure
under low-cycle loading is substantiated. It is shown that, unlike traditional structural
materials, the dissipated energy does not affect the fatigue life of pseudoelastic SMA.
A method for predicting the durability of a pseudoelastic SMA under low-cycle fatigue
with constant amplitude taking into account the stress ratio and the variable amplitude is
developed. This method is based on the fatigue fracture criterion, total elastic energy density
determined under constant amplitude. The relative error between calculated and
experimental data does not exceed 30.1% and all calculated durability values are within the
2.5 predicted range. The method for quick determination of parameters in the fatigue
fracture model based on the criterion of total elastic energy density according to the test
results under quasi-static uniaxial tensile loading at constant amplitude.
Keywords: pseudoelastic NiTi alloy; functional fatigue, structural fatigue, dissipation
energy, total elastic energy density, hydrogen embrittlement, stress ratio, variable amplitude,
fatigue crack growth, damper device