박판의 포아송의 비 측정을 위한 길이 결정

Abstract

The Poisson's ratio is one of the important factors which uses in the whole field of the stress analysis and the structure dynamics. However, the material properties of sheet material may not be the same as those of the bulk one. Moreover, the process by which the sheet material is deposited affects the material properties. Thus, it is important that determine the mechanical properties of micro material in order to predict the performances of micro structure devices. Because sheet material have thickness of the order of microns, the measurement methods used for bulk materials are no longer appropriate. Various testing technique to determine the properties of thin film have been investigated such as Nano indentation test, Bulge test, Micro tensile test and so on. They each have strength and weakness in the preparation of test specimen and the analysis of experimental result. Recently, optical techniques have been developed for measuring mechanical properties. Among these methods, an effective technique is the use of a cantilever beam load by various means. In order to find out the Poisson's ratio, in this research the Time-averaged Electronic Speckle Pattern Interferometry (TA-ESPI) is used. The proposed technique for measuring the Poisson's ratio of sheet materials whose thickness is 50um is expected to be used as an advanced non-destructive testing method with some merits, such as time-saving and non-contacting, in the MEMS field. TA-ESPI is one of laser speckle interferometry with the advantage of non-contact, non-destructive, high-resolution and whole-field measurement. The technique has been developed as a common method for visualizing vibration mode shape and measuring surface displacement. This research uses Euler-Bernoulli equation for a cantilever beam and fundamental torsion equation for a rectangular bar because of the dynamic Young's modulus and the dynamic shear modulus. A harmonically vibrating object has the maximum out-of-plane displacement at a resonance frequency. The resonance frequency depends on the material, the size, and the thickness of a specimen and the boundary condition. With the results, the Poisson's ratio can be determined accurately when the aspect ratio is more than decuple. And it is possible to reduce an error when the resonance frequency over the 3rd is used.