When an amplitude of a vibrator changes its frequency also changes. This phenomenon is called non-linearity of the vibrator. In this study, a tuning fork vibrator and a canti-lever vibrator is dealt. Non-linearity of the vibrator consists of geometrical non-linearity and material non-linearity. As shown in (Lit. 1), the frequency deviation of an ordinary beam vibrator owing to geometrical non-linearity is very small. Thematerial non-linearity means that the relation between stress σ and strain ε_s is not linear. In this study, two different relations(Eq. 1, 13) are assumed, and the frequency deviation due to them is calculated and compared with experiments. The results are as follows. (1) When the amplitude of stress of a beam vibrator( made of metal ) is small, the frequency deviation Δω/ω_0 is proportional to the amplitude Uo, as shown in Fig. 7.When the amplitude becones Large, the frequency decoes small. (2) When hysteresis is negligible, the relation between stress and strain can by shown (Eq.13 ),and the frequncy deviation is shown by (Eq.60).C_2 is shown in (Tad. 2) and ( Fig. 4) . According to experiments, E_1 /E_0 is 10〜100 for metals.
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