磁気ひずみ材料および電気ひずみ材料の疲れ試験

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The output power of magnetostrictive transducers and electrostrictive transducers in various ultrasonic power applications will be limited by three major factors. They are (1) Saturation of the driving force, (2) Maximum vibrational amplitude not to cause property degradation due to heat generation or temperature rise and (3) Mechanical fatigue limit of transducer meterials. The values of these factors have to be known for the proper design of vibrating systems that are used in high power applications. In this paper the authors measured the mechanical fatigue limit of the materials of ferrite magnetostrictive transducer and lead zirconate titanate electrostrictive transducer that are practically used today in ultrasonic applications. For the measurement of fatigne limit, we used the Improved Staircase Method that has been developed by I. Yosimoto and used in the field of metals. The Improved Staircase Method is a statistical one that comprises two steps of measurement;usual S-log N curve measurement and staircase measurement. A rough value of fatigue limit obtained from the S-log N curve measurement is used as the initial stress of the staircase measurement. By this procedure a sample mean and a sample standard deviation of the fatigue limit can be obtained. Using these values of the sample mean and the sample standared deviation, it is possible to perform Interval Estimation for the population mean of the fatigue limit. Bar-shaped testpieces made of the same materlials as ferrite magnetostrictive transducer and lead zirconate titanate electrostrictive transducer were provided by four factories. The vibrating system driving the testpiece consists of a ferrite magnetostrictive drive transducer, a metal resonance horn and a vibration pick-up. The testpiece was attached to the thin end of the horn, and set into the longitudinal vibration at 28 kHz resonance frequency. At longitudinal resonance the vibration stress in the testpiece become maximum at the center of its length, therefore fracture is supposed to occur at this position when the testpiece is homogeneous, and the fatigue limit of the material will be represented by the stress S_max at this position. When actually fracture did not occur at the center of the testpiece, only the data about the testpieces that broke within λ/36 from the center of the testpiece were adopted, λ being twice the length, of the testpiece, or the wave length, and the stress S at the position of the fracture was considered to represent the fatigue limit. Stress S within λ/36 from the position of stress maximum is as follows. 0. 985 S_max≦S≦S_max. S_max can be calculated from the density ρ, the sound velocity c of the testpiece and the vibrational velocity υ at the testpiece end which is known by the calibrated output voltage of the vibration pick up. As for metals, stress is to be applied as far as 10^7 cycles. But we increased the number of stress repetitions in the staircase measurement as far as 10^8, considering that the materials were ferrite and ceramics. It can be concluded from the results of the S-log N curve measurements that 10^8 stress cycles are sufficient for the staircase measurement of the fatigue limit. In conclusion, the fatigue limit of the ferrite material was estimated above 3 kg/mm^2. The fatigue limit of the lead zirconate titanate material also turned out to be above 3 kg/mm^2
社団法人日本音響学会の論文
1972-05-01

磁気ひずみ材料および電気ひずみ材料の疲れ試験

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