Ultrasonic fatigue system Ultrafast-WKK

Ultrasonic fatigue system Ultrafast-WKK

In order to be able to carry out tests with more than 10⁸ cycles in a reasonable time, an ultrasonic fatigue system “Ultrafast-WKK” was purchased within the context of the Cluster of Excellence “Engineering of Advanced Materials”. In this system, a piezo crystal is excited to a high-frequency oscillation, which is transmitted to a specimen via an amplifier system. The resulting frequency corresponds to the natural frequency of the sample and is typically around 20 kHz. A standing wave is formed in the specimen, resulting in a strain maximum in the center of the specimen. This can be determined by means of strain gauges and subsequently correlated with the total displacement of the specimen. The total displacement is determined at the freely vibrating end of the specimen using a laser interferometer. Thus, after some calibration tests, it is possible to determine the specimen strain during fatigue without contact.

However, the high operating frequencies (20 kHz) lead to significant specimen heating during loading. Which is why ultrasonic fatigue experiments are performed in a pulse-pause mode. Typically, the loading times are in the range of 250 – 500 ms, and the corresponding pause times can be 500 ms to several seconds. This results in effective fatigue frequencies of more than 2500 Hz.

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