The NAS vibration test is one of the standard methods for evaluating the loosening of threaded fasteners. In our previous study, we conducted tests using our existing vibration testing machine and analyzed the spectrogram of the sound generated during the tests. The results demonstrated that loosening can be evaluated in more detail through this approach. In this study, we investigated the cause of the sound generated during testing by performing a vibration mode analysis of the test fixture using both experimental methods and finite element analysis. It was shown that the natural frequencies of the test fixture coincide with the dominant frequencies of the sound generated during testing. The natural vibration modes of the test fixture provided useful insights for understanding and visualizing the phenomena observed. Furthermore, from a practical perspective, understanding the service life of the test fixture is essential. Therefore, the fixture was subjected to repeated use to evaluate its effect on the test results.
Akira MOMOSE (Wed,) studied this question.