| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 93 === Specimens of 3Y-TZP doped with various concentrations of YNbO4 were employed to perform cyclic tension-compression loading, interlaced with creeping at diverse stress levels. The specimens are in the form of thin plate, hence ensuring uniformity of stress distribution across the thickness. The occurring intensity and type of toughening mechanisms and the interactions among them are identified at different stress levels. The effect of YNbO4 on toughening mechanisms was detected by differentiating its concentration in the specimens.
The fluctuation of Poisson’s ratio is flabbergastingly huge, say, from –3.87 to 6 for some specimen, when subjected to tensile stress, attributed to intense occurring of phase transformation. Some of the corresponding stress-strain loops in the tensile portion even appear counterclockwise, indicating that energy is released from specimen, contrasting most engineering materials. The stress-strain loops in the tensile portion also exhibit substantial vacillation, implying that tensile stress is prone to trigger phase transformation. The intensity of phase transformation subsides as the cycle number increases. While subjected to compressive stress, the Poisson’s ratio basically stays very close to the elastic Poisson’s ratio, showing that no significant phase transformation takes place. Raising the concentration of YNbO4 facilitates phase transformation, but curbs it when the concentration is beyond a certain value.
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