Four-axis high-frequcncy structural strength fatigue test system

High cycle fatigue testing to long lives requires high frequency equipment. The working frequency of the conventional electrohydraulic vibration exciters in fatigue test system is limited to fairly narrow range by the frequency response capability of the servo valve. In response to these needs, a four-axis structural strength fatigue test system capable of frequency and amplitude controlled testing at 5~200 Hz has been developed. The four-axis structural strength fatigue test system includes four electrohydraulic vibration exciters mounted in horizontal and vertical structural frame respectively. This electrohydraulic vibration exciters include 2D valve, double acting cylinder and bias control servo valve etc. In the 2D valve, the rotary and sliding motions are independently exploited to control the frequency and the magnitude of the vibration respectively. The frequency of the 2D valve controlled vibration exciter is determined by the rotary speed, number of grooves distributed on a spool land and coupled pattern of the groove's number on the spool land and the window's number on the spool sleeve. By adjusting these factors in the 2D valve design, the proposed scheme of vibration exciter is apt to realize high-frequency vibration and to increase the working frequency of multi-axis structural strength fatigue test system. In this paper, the structure of test system is first described. Then, the principal of the electrohydaulic vibration exciter using 2D valve is discussed, which includes the control method of frequency, amplitude and phase. The dynamic characteristics of electrohydaulic vibration exciter in test system are briefly discussed. Finally, the measured vibration wave is given to validate the theoretical analysis. Four-axis structural strength fatigue test system formed by the electrohydraulic vibration exciter using 2D valve has now been put into practical operation as a standard fatigue testing device. It is classified that the vibration of the tested object can be excited synchronously in four-axis with the frequency 5~200 Hz adjustable or excited with in one-axis solely.