抄録
The natural frequencies of the beam subjected to tensile or compression stress vary in proportion to the magnitude of the loading stress. A round bar with both rigid ends was subjected to the stress and impacted by a small ball. By FFT analyzer, natural frequencies of the bar were measured using the impact sound, and working stress in the bar was measured by strain gauges. Vibration equation for a bar with both rigid ends and subjected to an axial stress was analyzed and theoretical relation between applied stress and natural frequencies was obtained. The relation between applied stress and natural frequencies of the round bar by the experiment and by the theory was compared. They agreed with about 5% difference. Impact sound may be one of effective methods to measure working stress in a bar subjected to an axial stress.
