Degradation of functional properties of pseudoelastic NiTi alloy under cyclic loading: an experimental study

Abstract

The influence of the cyclic loading on the functional properties of NiTi was studied. Cylindrical specimens with adiameter of 4 mm and a gage length of 12.5 mm were tested under uniaxial cyclic loading with control crosshead displacement ata temperatureof 0°С. The dependences of the stress and strain range as well as dissipation energy on the number of loading cycles at different initialstress rangewereanalysed. During the first10loading cycles,arapid decrease inthe strainrange and energy dissipation wasobserved.Dissipation energy wasinvariant to the loading cycles’number at N > 20 cyclesand to the stressrange thatdidnot exceed the martensite finish stress level, waswithin the same scatter band and can be described by the single dependence. With the stress range growth at N < 20 cycles from 509 to 740MPa,the value of dissipation energy increases and thatof relative dissipation energy decreases.Loss coefficient,which characterises material damping ability,significantly decreases during the first 10 loading cycles and remains practically unchanged up to the failure of the specimens. At the stabilisation area,the loss coefficient is almost non-sensitive towards the stressrange.