GIANT-MAGNETOSTRICTIVE VIBRATOR SYSTEM FOR FRETTING TESTING AT LOW AMPLITUDES

In fretting testing, measurements of frequency and applied forces can be made with good accuracy. For small displacements (less than 2 mum), however, the uncertainty of measured displacement or slip in the fret ting contact is substantial. This is because of the fact that most exp eriments are designed simply to measure the displacement of the specim en to which the vibrations are fed. In practice, however, the vibratio ns also propagate through other parts of the machine and through the f retting contact surface to the ''stationary'' specimen. The result is that the relative displacement will be overestimated, particularly for low amplitudes. In order to overcome this problem, a machine has been built with the following design principles. Tangential vibrations are applied to one specimen, while damping characteristics of the major p arts of the testing machine are chosen so as to minimize induced machi ne vibrations of the mating specimen. In addition, displacement measur ements are performed by optical methods, on both specimens, thereby se curing the possibility of representing the results in terms of the rel ative displacement. A giant-magnetostrictive actuator has been develop ed, which generates extremely well-controlled vibrations. Experiments, data acquisition and post experiment data treatment are fully compute rized. The final results are enhanced by off-line digital noise reduct ion. The paper gives a description of the complete system, and some re sults of an evaluation test series.