Ultrasonic reflection characteristics that vary with wrinkling enable the detection of wrinkles during press forming. In this study, we investigated the influence of wrinkles on ultrasonic reflection characteristics by Finite-Difference Time-Domain (FDTD) analysis and experiments with model specimens. The wrinkle shape on the model specimen was made into a trapezoid by electric discharge machining. FDTD analysis was performed using the analysis model that reproduces experimental situations. The first reflection wave occurring at the lower surface of the upper die affected the ultrasonic characteristics, which changed with wrinkle wavelength. The effective diameter of the ultrasonic probe and the irradiation diameter of the ultrasonic wave also affected the ultrasonic reflection characteristics. In the region where the ratio of the irradiation diameter of the ultrasonic wave to the wrinkle wavelength is 0.3 or more, the reflection intensity depends on the irradiation position of the ultrasonic wave. The irradiation position at the maximum reflection intensity varies depending on the fraction of the effective diameter of the ultrasonic probe and the wrinkle wavelength.
This study suggests a novel method to detect wrinkles using the frequency characteristic of reflected ultrasonic wave. The experimental apparatus was manufactured to simulate the press forming. A plate specimen possessing periodic wrinkles in a trapezoidal shape was also prepared to simulate actual wrinkles during the press forming process. These wrinkles affected the reflected wave of ultrasonic wave. The power spectrum of reflected wave at a frequency of 0.8 MHz was changed by the occurrence of wrinkles. The comparison of the frequency characteristics provided obvious difference between wrinkled and flat specimens. As a result, the present work confirmed that the frequency characteristic of reflected wave would detect the formation of wrinkles.
In this article, the investigation of the use of a rolling particle damper under sinusoidal excitation is described. A rolling particle damper is a type of ball vibration absorber and consists of a rotating cylinder placed on a curved track mounted on a primary system. The rotating cylinder is partially filled with granular materials. When the rotating cylinder rolls inside the curved track, the granular materials also move. The friction between the granular materials and the inside wall of the rotating cylinder results in some energy dissipation. A rolling particle damper can be adopted in a harsh environment because it can be operated in a wide temperature range. The effects of the mass ratio, the particle material, and the particle diameter on the damping performance were examined experimentally. To elucidate the behavior of the entire system in detail, a numerical solution using the discrete element method was established. The predicted damping results were compared with experimental results for various mass ratios. In addition, the effect of the frequency ratio on the highest displacement amplitude of the primary system was examined referring to the numerical results.
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