Abstract
Ultrasonic fatigue testing machine are being used to perform materials testing in the range of 10E9 to 10E10 fatigue
cycles. The so-called very high cycle fatigue regime is now under intense studies in which concerns the lay-out of
ultrasonic fatigue testing machines. Nevertheless, the accurate measurement of the parameters that influence fatigue life
(stress, strain, displacement …) at ultrasonic frequencies still is a matter of concern and continuous development. The
objective of this paper is to describe the design and construction of an ultrasonic fatigue testing machine at 20 kHz
working frequency. In order to achieve fully automated tests, a closed loop control system was developed to use
monitored temperature and displacement to set the power and the cooling periods of the machine. The monitoring of the
displacement, considered here in the bottom face of the specimen, is carried out using a high resolution laser. The
specimen´s temperature is monitored online through a pyrometer. To manage and process, a data acquisition device
working at 400 kHz from National Instruments is used. The software was developed in house using the LabView
package. The present paper describes the advantages and drawbacks of metal fatigue testing at very high frequencies.