PSI - Issue 5

G. Lesiuk et al. / Procedia Structural Integrity 5 (2017) 928–934

933

Lesiuk et al./ Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 8. Fatigue lifetime of specimen with and without current pulse (AISI 304 steel)

Tang et al. (2013) demonstrate the similar effect in SUS316 steel (Fig. 9). However, in this paper the S-N curve was obtained using crack initiation as a failure criterion. Based on Tang et al. (2013) it more likely that this effect is strongly dependent from the fatigue micro crack formation phase. As it is noticeable, for low stress amplitudes the differences in fatigue lifetimes are much higher than for high stress level. It means that this effect should be associated not only with the ordinary local heat treatment of the specimen, but it is strongly supported by the microstructure transformation process caused by the high speed heat transfer. In several papers by Song et al. (2008), Wang et al. (2009) the microstructure changes (obtained in Ti-alloys) have been demonstrated. The electro pulsing itself can promote recrystallization. According to Sprecher and Mannan (1986) it is worth to underline that the in a current-carrying metallic material, the possible drift electrons can involve an extra force on dislocations motions. This force is so often called “ after electron wind force ”. Its value is proportional to current density. Due to this possible effect, the mobility of dislocation will be increased during electropulsing treatment. Therefore this effect can be reflected in static properties as well as in fatigue properties of metals.

Fig. 9. S – N curves of stainless steel (SUS316) with and without electropulsing – results obtained by Tang et al. (2013).

4. Conclusions In the work the (first) initial results for the fatigue tests of the selected specimens subjected to the current exposure are presented with the aim of obtaining information on possibilities of increase in the fatigue lifetime caused by the current stimulation. The stimulation was aimed at initiation of the electro plasticity phenomenon. The positive current pulses of different duration and frequency were applied. The tests were performed with the MTS 810 hydraulic pulsator, controlled with constant amplitude of force F max =1100N ( R =0.1, f =25Hz). The recorded