The Inelastic Deformation of Tetragonal Zirconia Polycrystals Subjected to High Compressive Stress

• Main Authors: Wen-chu Liao, 廖文助
• Other Authors: Chien-hsien Liu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/4837k5

碩士 === 國立臺灣科技大學 === 機械工程系 === 95 === Specimens of 3Y-zirconia tetragonal polycrystals, doped with various concentrations of YNbO4, were subjected to high compressive stress cyclic loading. Creeping at the upper and lower ends of some cyclic loading was also performed. The specimens are in the form of a thin plate to ensure a plane stress loading in the central portion where the longitudinal and transverse gages are bonded. The instantaneous Young’s modulus, instantaneous Poisson’s ratio and instantaneous bulk modulus, along with the stress-strain curves and stress-volume dilatation curves, were analyzed to reveal the occurring intensity of various toughening mechanisms, such as domain reorientation and phase transformation, at different stress levels. An abrupt increase of the fluctuation of the instantaneous Young’s modulus, instantaneous Poisson’s ratio and instantaneous bulk modulus was perceived when the compressive stress reaches some high level, such as –1625 and –1629 MPas for 2 and 4 mol% specimens, respectively. Before these critical levels, these three instantaneous mechanical properties increase gradually, but stay close to their corresponding elastic values. Intriguingly, in the beginning of loading, these instantaneous mechanical properties also fluctuate in a much more moderate extent than after the critical stress levels. It’s been found that some volume-dilatational phase transformation takes place massively after the critical values, producing substantial inelastic deformation to offset the elastic one. At some stress point, the material exhibits incompressibility with an instantaneous Poisson’s ratio of 0.5. The phase transformation appears to be undone by its reverse transformation during unloading. It’s noteworthy that the phase transformation seems to occur significantly right in the beginning of loading.