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Stress Measurement by Spectrum Analyses for Round Bar Subjected to Time-Varying Load

In this research, a feasibility study to measure the magnitude and cycle of the time-varying stress of a specimen using the natural frequency was carried out. An experiment was conducted. We used a round bar with 8 mm diameter and 290 mm span length as a specimen, which was fixed at both ends. A sinusoidal axial stress was applied to the bar. The deflection of the bar in free vibration was measured using a laser beam displacement device. To collect more information on the deflection, a device was made, which hit the bar periodically. The fast Fourier transform method, short-time Fourier transform method and wavelet analysis were applied to the deflection. The methods gave us relations among time, frequency and magnitude of the signal, with complicated representations. Applying the analyses to the experimental data, we tried to evaluate the magnitude and cycle of a time-varying load.