Measurement of Coefficient of Thermal Expansion by Digital Image Correlation

• Main Authors: Jing-Jhih Fang, 枋靚
• Other Authors: Shun-Fa Hwung
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/n4t5a8

碩士 === 國立雲林科技大學 === 機械工程系碩士班 === 101 === The aims of this paper which divided a digital image correlation (DIC) into a two-step DIC and three-dimensional digital image correlation (3D-DIC) are to measure the coefficient of thermal expansion (CTE) of materials. First, a two-step DIC is applied to measure the CTE of three kinds of materials, aluminum, composite material, and polydimethylsiloxane (PDMS), respectively. Under temperature increments several images of deformed specimens are taken to search the displacement and strain, and then the CTE of the specimens could be calculated. In the two-step DIC, in addition to that strains are superimposed from the comparison of neighboring images, strains obtained from double regions are also used and compared. The measured CTE for aluminum specimen verifies the feasibility of this two-step DIC and the reliability of the strains obtained from either neighboring images or double regions. The measured CTE of carbon fiber reinforced composite material is close to zero or even a negative, and the change of the constituent fraction of PDMS specimens could vary their CTE. Second, 3D-DIC is used to measure the radius of a bottle with fixed curvature to verify this method. Moreover, three kinds of speckle patterns are investigated to compare their effects on the results of radius. The results indicate that the speckle patterns that are directly sprayed on the bottle have nice results on the obtained curvatures with the error of 0.372%. After the verification, the curvature of double materials is measured, and the CTE of the target material can be calculated. The double materials consisting of brass and resin are combined in a plate form in high temperature and then cooling to room temperature. Because of the difference on the CTE of these two materials, the fabricated double materials will produce curvature. 3D-DIC is applied to measure the radius of double materials and Stoney formula is used to calculate the CTE of resin, and the measured CTE of resin used in this paper is about 93~96×10^-6 m/℃.