Abstract
NAS vibration testing is one of the typical methods to evaluate loosening threaded fasteners. Using a jig based on NAS3350 and a commonly used vibration exciter, loosening tests can be performed without a specialized tester for the evaluation. Basically, the only result obtained from the NAS test is the time from the test start until the fastener is disassembled. It has been difficult to understand how fasteners would loosen during the test. The purpose of this study was to investigate its behavior on the test. The tests were conducted for M8 bolt (strain gauge is embedded axially) and nut fasteners using existing vibration testing machine. Time history of the strain that is related to bolt axial force was obtained during testing. The sound pressure induced during the vibration testing was also measured at the same time. Time-frequency analysis of these measured data was performed using the short-time Fourier transform to obtain the distribution of the sound spectrogram. From these results, it has been achieved to determine when the fastener is completely loosened by measuring sound pressure.
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