| Summary: | 碩士 === 國立雲林科技大學 === 機械工程系 === 104 === The advantage of digital Image Correlation method (DIC) is the ability to measure the displacement without contacting the object. By taking the images of object before and after machining, the displacement occurring to the surface of object can be calculated. Before calculating displacement, an appropriate size has to be set for the reference subset. Reference subset size is an important parameter for DIC. If the subset size is too small, analytical failure is likely to occur. If the subset size is too big, it is difficult to acquire accurate displacement in a small area. Therefore, the first goal of this paper is to investigate the size of reference subset. The feature points within the subset were searched initially by using image morphology, then calculated displacement using different sizes of reference subset, and finally transformed displacement into strain data. According to the experiment results, strain data tended to be more stable if the size of reference subset was larger than the largest size of feature point. Therefore, it is essential to acquire the proper size of feature point for determining the size of reference subset before calculating DIC.
The second goal of this paper is to investigate a drilled square slot in a four-point bended aluminum alloy specimen by using wire electrical discharge machining method (w-EDM), then the displacement on the surface of square slot was observed, and transformed the displacement into strain data. Six specimens with different bending degrees were employed for the experiment. Experiment results indicated that the larger the bending degree, the larger the deformation. The displacement on a plane was measured by using DIC. The experiment results indicate the good correlation between the bending degree and measured displacement. However, the accuracy is limited due to the out-of-plane deformation was not considered in this paper.
The third goal of this paper is to investigate the drilled holes in aluminum alloy specimens were drilled by using laser machining equipment, then observed the deformations around the holes using various auxiliary mechanisms. According to the experiment results, laser machining produced high temperature and large thermal gradient that yields thermal stress for the specimens. Thermal stress causes the thermal deformation. By employing jet auxiliary mechanism and thermal grease to increase thermal gradient, larger thermal stress was produced for the specimen, and consequently yields larger thermal deformation. When specimen was preheated to a temperature approximately 150℃, the larger thermal deformation was observed because of the thermal expansion effect of the metal material.
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