Issue 50

V. Iasnii et alii, Frattura ed Integrità Strutturale, 50 (2019) 310-318; DOI: 10.3221/IGF-ESIS.50.26 315 Figure 4 : Dependence of the dissipated energy on the number of loading cycles in ice water at 0°С and at 20°С in the air. The constant values   W and   W of the Eqn. (10) were determined by the approximation of the experimental data using the least squares method are presented in Tab. 2. T, °С   W   W R 2 A W B W R 2 Eq. (10) Eq. (13) 0 9.974 ±1.604 0.3537 ±0.0351 0.950 142.6 0.663 0.709 20 2.478 ±1.253 0.3148 ±0.092 0.949 148.4 0.0925 0.924 Table 2 : Equations parameters for Ni55.8Ti44.2 alloy. In the Eqn. (10), the energy of dissipation was determined in the same way as in the previous cases at the number of half- cycles to failure. The fatigue life of the NiTi alloy increases with the decrease in test temperature when using the strain range (Fig. 2), as well as dissipated energy (Fig.4). The influence of testing temperature on accumulated dissipation energy before failure was analysed. The accumulated dissipation energy was determined by formula 1 , f N dis i i W W     (11) where  W i is the dissipated energy for i -th loading cycle. As the first approximation, the change in the area of hysteresis loop during first cycles could be neglected. In this case, the formula (11) can be rewritten as follows: , dis f dis N W W    (12) where  W dis is the dissipated energy at mean lifetime N f . As in the case with Odqvist's parameter, the experimental values of total dissipated energy could be described by a linearly proportional dependence on cycles to failure