High-power, ultrasonic fatigue testing machine

Abstract

A machine capable of fatigue testing high strength alloys at an ultrasonic frequency (20 kHz), and a range of temperatures likely to be encountered by such materials in aerospace and power generation applications and in basic research, is described. The machine is assembled entirely from commercially available components used in ultrasonic joining processes. Basically, it consists of a power supply module and heavy duty transducer capable of delivering up to 1.2 kW of acoustic energy at peak-to-peak amplitudes ranging from 10 to 20 /-L, which is further amplified by tuned acoustic horns. The machine sets up a 20 kHz standing wave in the resonant test specimen. Peak-to-peak displacement amplitudes in the specimen of up to 300 /-L (typical stress levels up to 1400 MN/m2) can be achieved. Provisions have also been made to accurately monitor the frequency of testing and the displacement amplitude during the test. As an example of the capabilities of the machine, results of high-frequency fatigue tests performed over a range of temperatures are presented. Lastly, it is indicated that ultrasonic fatigue testing, by virtue of its extremely high rate of testing, can be conveniently used for the study of very slow fatigue crack propagation in engineering alloys.

Development of Ultrasonic Fatigue for Rapid, High Temperature Fatigue Studies in Turbine Engine Materials

“…More recently, Mayer has offered a comprehensive review of improvements in the past ten years, especially regarding the use of ultrasonic fatigue for fatigue crack growth threshold studies [20]. In the United States, early work was begun by Tien and coworkers in the late 1970s and early 1980s [21,22] but in recent years, research effort has been concentrated primarily in Japan and Europe, where the technique is enjoying considerable use there as a tool for very long fatigue life prediction [23,24]. The growing interest in ultrasonic fatigue is driven in part by the increased need to predict lifetimes in aging structures and is made possible by dramatic improvements in the accuracy of control instrumentation for ultrasonic fatigue.…”

HIGH CYCLE FATIGUE AND THRESHOLD BEHAVIOUR OF POWDER METALLURGICAL Mo AND Mo-ALLOYS

“…The experimental data were statistically evaluated using various mathematical functions to correlate fracture probability with cyclic stress or loading cycles [14]. As an example, the facture probability is plotted versus cyclic stress in a normal (gaussian) distribution graph, see Fig.…”