ABSTRACT
Up to now, there have been no standards for testing procedures and testing machines of ultrasonic fatigue, although efforts are in progress within ASTM to provide a recommended practice and ultimately a testing standard (Bathias, 1998). Because of this, laboratories must develop their own machines and design practical test procedures. The laboratories of Willertz in the United States, Stanzl in Austria, Bathias in France, Ni in China, Ishii in Japan, and Puskar in Slovakia are among the leading laboratories in this field. Although ultrasonic fatigue test machines in these laboratories are not the same, some components are common to all machines. The three most important are: (1) a high frequency generator that generates 20kHz sinusoidal electrical signal, (2) a transducer that transforms the electrical signal into mechanical vibration, and (3) a control unit. Early ultrasonic fatigue machines performed only uni-axial
(one-dimensional) and constant amplitude tests, so the control unit and other parts were not very complicated. In the last two decades, progress has been made to extend the ultrasonic fatigue technique to variable amplitude loading conditions, low or high temperature environments, torsional or multi axial tests, and so on. Thus, designing a modern ultrasonic fatigue test machine may involve mechanical, electrical, optical, magnetic, and thermal considerations. In France, Bathias used a first ultrasonic fatigue test machine in 1967 on the principle used by Mason (Bathias, 1998). As indicated in an early review paper (Stanzl, 1996), the rather restrictive uses of the ultrasonic fatigue test method appeared to be partly due to the lack of commercially available test equipment, forcing the individual investigators to work with improvized facilities not readily amenable to standardized experimental conditions.
