| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 91 === There are three major toughening mechanisms in zirconia: ferro-elastic domain reorientation, martensitic phase transformation and micro-crack toughening. Specimens of 3Y-Zirconia doped with various amounts of were utilized to perform an extensive uni-axial compressive loading program. The occurring intensity and interaction of these toughening mechanisms at different stress levels were investigated.
It was further confirmed that domain reorientation is fully reversible. There exists a static stress-strain loop. The stress-strain curves of various stress rates deviate from the static stress-strain loop, but always approach to it when creeping at some stress level. It is very intriguing to notice that when loading from the stress-free state without residual domain reorientation and creeping at some stress level, domain reorientation keeps activating until axial strain reaches a certain value; while reverse domain reorientation keeps operating until axial strain approaches in the reverse direction to the same value if with residual domain reorientation from previous loading. Resuming loading after creeping at certain stress level, the stress-strain curve approaches to and then coincides with the one obtained without creeping at the stress level. Those inelastic deformations attributed to domain reorientation are fully recoverable and will reach the same state at a certain stress level regardless of loading history.
It is quite likely that tetragonal-to-monoclinic phase transformation is also fully reversible. However, more evidence is needed since the occurring occasion of intense phase transformation is unpredictable. For this purpose, a novel fixture, able to carry out a combined loading of tension, compression and torsion, is proposed for further experiments.
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