DESIGN AND INSTRUMENTATION OF AN ULTRASONIC FATIGUE TESTING MACHINE

摘要

Ultrasonic fatigue testing machine are being used to perform materials testing in the range of 10~7 to 10~(10) fatigue cycles. The so-called very high cycle fatigue regime is now an established technology in which concerns the lay-out of ultrasonic fatigue machines, but the accurate measurement of the parameters that influence fatigue life (load, 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 a fully instrumented 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. The cooling of the specimen is achieved with cooled dry air. To manage and process the data a data acquisition device working at 400 kHz from National Instruments is used. The software was developed in house using the LabView package.