Instumentation of Ultrasonic High-Frequency Machine to Estimate Applied Stress in Middle Section of Specimen

The objective of this paper is to describe the instrumentation of a new developed ultrasonic fatigue testing machine at 20 kHz working frequency and compare the possible solutions to estimate the stress applied in the middle section of the specimen. Stress is estimated by measuring the displacement on bottom of the specimen and their strain on middle section. The monitoring of the displacement, considered here in the bottom face of the specimen, is carried out using a high resolution laser, the strain using a strain gauge in middle of specimen and field temperature using a pyrometer and thermographic camera. A LabVIEW routine is used to control the initial parameters of the transducer, such as the frequency reset, the frequency seek, the load amplitude and to record data of all sensors. To manage and process the data, a data acquisition device working at 400 kHz from National Instruments is used.