this invention is an improved system for the vibration - testing of cantilevered non - ferrous articles by inducing eddy currents therein . the principal advantage of the system is that relatively little heat is generated in the article being vibrated . thus , a more accurate measurement of the fatigue characteristics of the article is obtained . furthermore , the generation of relatively little heat in the blade permits tests to be conducted in low - pressure atmospheres simulating certain actual processes environments . heat - generation in the vibrated article is minimized by utilizing eddy currents which are generated by an electromagnet whose magnetic field varies but does not change polarity . the typical winding for the electromagnet is excited with pulsating d . c . that is , the winding is alternately charged by connecting it across a d . c . power supply and then discharged by connecting it across a circuit for receiving current generated in the winding by self - induction . preferably , the discharge circuit is designed so that the waveform of the discharging current approximates that of the charging current .