ULTRASONIC FATIGUE ANALYSIS ON STEEL SPECIMEN WITH TEMPERATURE CONTROL: EVALUATION OF VARIABLE TEMPERATURE EFFECT

Ultrasonic fatigue testing machine are being used t o perform materials testing in the range of 10E9 to 10E10 fatigue cycles. The so-called very high cycle fatigue regim e is now under intense studies in which concerns th e lay-out of ultrasonic fatigue testing machines. Nevertheless, the accurate measurement of the parameters that inf luence fatigue life (stress, strain, displacement …) at ultrasonic freq uencies still is a matter of concern and continuous development. The objective of this paper is to describe the design a nd construction of an ultrasonic fatigue testing ma chine at 20 kHz working frequency. In order to achieve fully automa ted tests, a closed loop control system was develop ed to use monitored temperature and displacement to set the p ower 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 resoluti on laser. The