Sound and Vibration Measurements of Metal Plates

University essay from Blekinge Tekniska Högskola/Sektionen för ingenjörsvetenskap

Abstract:

Abstract The purpose in this project is to classify different metal plates according to their size and material. The plates which are studied are small plates with the maximum size of: radius=25.75 mm and thickness=2.20 mm. The quantities of interest are the natural frequencies of the plate which may be estimated experimentally based on the plate's frequency response function (FRF) estimate produced using the measured input force signal applied to the plate which had been recorded simultaneously with the output vibrations of the plate. The small size of the studied plates makes the measurements different from the rdinary sound and vibration measurements. The difference was basically in the sensor size and excitation method due to the small size of the studied objects. As in the case of small plates, it was necessary to find a suitable excitation method which could excite the natural frequencies of the plates. Plates different in geometrical dimensions as well as having different material properties are likely to be distinguished by their natural frequencies. Plate vibrations were excited using two methods: impact excitation by means of an impulse hammer and shaker excitation. In the studied structures in this project, the plate is excited by a random or transient input signal. The vibrations of the plate are measured using an accelerometer or a laser vibrometer. Repeatability of the measurements was one of the important interests which we tried to fulfill. But the first and most important goal was exciting and measuring the natural frequencies of the plate apart from the natural frequencies of the other components of the system. In most of the structures it was difficult to excite the natural frequencies of the plates due to the small size of them. To solve this problem, different boundary conditions of the plates are studied.

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