| Summary: | 碩士 === 國立成功大學 === 土木工程學系碩博士班 === 95 === Non-Destructive Testing (NDT) is a testing method for detecting and measuring the qualities or defects of objects, such as thermography, ground penetrating radar, etc. Thermography, one of the NDT methods, evaluates the subject according to the surface temperature of the subject. As the object has a void inside, the surface temperature of the void will differ from the solid area at the same specimen. The void can be distinguished by the surface temperature difference. Although thermogrophy is convenient for detecting the inner void of the material, it is not easy to detect the exact size and depth of the void. The information of the surface temperature variation associated with the size and depth of the void and the environment conditions, such as the heat source and the environmental temperature, is deficient in the evaluation process. By using the numerical simulations to obtain the information of exact qualities and quantities that can make the results of detection clearly.
Therefore, this thesis tried to find the way that can detect the subsurface void of the concrete plate exactly through the lab experiments and the numerical simulations. The sand box full of sands with a surface covered by the concrete plate was used in the lab experiment. The void behind the concrete cover was simulated by polystyrene cube. The heating time and the depth of the simulating void were varied in the experiments, meanwhile, the numerical model was created and revised to fit the results of the experiments in different conditions. Then, the revised numerical model was applied to simulate the surface temperature of the concrete plate under different materials, sizes and depths of the void, and different heating time and heating sources. Finally, this thesis tried to create the process of evaluating the size of the void based on the results of the numerical simulations.
After a series lab experiments and numerical simulations, some conclusions could be made as follows:
1.The temperature of the void has the high correlation with the thermal property of the sands around the void. When the thermal conductivity of the void is higher than the sands, the surface temperature of the concrete plate over the void would be high. On the other hand, the surface temperature of the concrete plate over the void would be low as the thermal conductivity of the void is lower than the sands.
2.As the sandbox was heated for three hours, the |△T| of the voids simulated by polystyrene will increase until eighty minutes, and then decrease. But, the |△T| of the voids built by cement mortar will decrease after one hundred to two hundred minutes in the same heating time.
3.The absolute temperature difference was directly proportional to the surface of the void, but inversely proportional to the depth of the void.
4.If the size of the void is fixed, the temperature difference would not be influenced by the variation of the size of the sand box
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