PSI - Issue 5

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

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

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mechanical effect in the form of the reverse magnetostriction phenomenon use (Zimniak and Hankiewicz, 2006) Such use of magnetic field and mechanical response of a material enables obtaining a series of interesting applications of this issue in the engineering practice – e.g. in a form of magnetovision camera described by Kaleta et al. (2009a, 2009b). Relatively little known the cross phenomenon is the effect of the impact of external electrical field on mechanical properties of the tested material. The phenomenon is called the electroplasticity and already in 1954, Cohen and Barrett (1954) observed the influence of electrical field on grain boundaries of the metallic material. Another group of Authors of works Machlin (1959), Troitskii and Likhtman (1963) documented the impact of that phenomenon on ductility of a material and its ability to deform. At that background the evaluation of the phenomenon impact on fatigue properties seems to be interesting. An interesting application of this phenomenon is the possibility of „curing the cracks” in the steel structural components (Song and Wang, 2008). However, little space is devoted in literature on use of this phenomenon in the fatigue research, and therefore this work presents the initial results of the tests by the Authors in this field. In the technological context the products obtained by means of different methods of plastic working and the tools used in these processes are very frequently exposed to fatigue loads. Increasing the fatigue durability becomes the key issue e.g. in the aviation industry or the operation of forging tools.

2. Experimental procedure

2.1. Material and specimen The object of the research were flat specimens with notch made of the AISI 304 austenitic stainless steel (0.04%C, 1.1%Mn, 0.41%Si, 0.0437%P, 0.0044%S, 18.16%Cr, 8%Ni, 0.0335%Mo, 0.1%V, 0.32%Cu) presented in Fig. 1.

Fig.1. Flat specimen scheme used in the experiments

The specimens with a lateral stress concentrator (k t =5.88) calculated in accordance with the work of Pilkey (1997) were prepared for the tests. In the research the specially developed generator of high-current pulses working with application of a supercapacitor was applied. Supercapacitors operate at the principle of using the phenomenon of the double layer of Helmholtz, which constitutes the area at the boundary of two phases with a statistically uneven distribution of electrons or ions in both phases. The great capacities are obtained by means of using very large contact surface of the carbon electrodes material (the capacities are about 10 000 times higher than in traditional capacitors). The biggest advantages of supercapacitors are: high impulse power, high density of energy, life time, and high efficiency (from 84 to 95%). Advantage of the supercapacitors is also a high number of work cycles, which may amount to even over a million. The most important parameters of the current generator are: maximum working voltage 2,7 V, capacity of a bank of capacitors 14 000 F, impedance of a single capacitor < 200μΩ, maximum value of the pulse current 15 kA. The