Vibration characteristics of NiTi-Al MMC beam fabricated with ultrasonic welding

摘要

A free-vibration differential equation of the compound beam of NiTi-Al MMC (metal matrix composite) is built considering the recovery stress of NiTi foil and based on Timoshenko beam theory to predict the frequency tuning characteristics of the compound beam. The clamped-free (CF) beam is under compressive stress state due to the recovery stress in the NiTi foil, which may cause a reduction in its natural frequency. For an 80 mm CF beam with 8% NiTi (prestrain 3%) embedded in Al matrix, the natural frequency decreases by 52.1% when temperature is up to 70 degrees C. However the stress state of clamped-clamped (CC) beam depends on the combined effect of recovery stress and thermal expansion of NiTi. At least 20% NiTi should be embedded in Al matrix to increase the natural frequency of CC beam. Finally, the NiTi-Al MMC beam is prepared by ultrasonic welding process. A thermal modal experiment is conducted to study the vibration characteristics of the compound beam. The results show that the natural frequency of the compound beam could be tuned effectively by volume fraction of the NiTi embedded in Al foil, which is consistent with theoretical calculations.