インパルス応答法による構造物の非線形性の推定法

抄録

In this paper, an estimation method of nonlinearities in mechanical structures is proposed with impulsive response methods, which are conventionally applied to the linear structures. Their efficiency is verified experimentally on the model structures with nonlinear spring characteristics, which are a bearing supported shaft and a bolted beam. The following results are obtained. In the time domain, the relationship between the average amplitude (AA) and the equivalent logarithmic decrement (ELD) as well as the relationship between AA and the equivalent natural frequency (ENF) can show qualitatively the existence, the intensity and the type of nonlinearity. In the frequency domain, the transfer functions such as Bode plots, Nyquist loci and their dependencies on exciting forces can show clearly the existence of nonlinearity in the structures. For instances, the structures have the characteristics of hardening springs, if ELD increases and ENF decreases as AA becomes smaller and the center of Nyquist loci rotates to the counter clockwise. And if these behaviour has opposite tendencies, the structures have the characteristics of softening springs. The experimental results show good agreements with the results from the theoretically proposed methods.