Sustematization Study of Toughening Mechanism in Ceramic-based Composites for Structural Use

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Main perpose of this project is to establish the universal standerd for evaluation and to systematize the toughening mechanism for structural ceramics and ceramic based composites. As the result of this project, ceramic-based materials can be classified the following three categories : (1) Brittle ceramics ( K_<IC> values of them are less than 5 MPa m^<1/2> ) (2) Toughened ceramics ( K_<IC> values of them are 5-10 MPa m^<1/2> in a general sense, and they almostly shows the some toughening-enhancement mechanisms during the crack extesion ) (3) Fever-reinforced ceramics ( They have microfracture processes accompanied by the main crack extension of fiber-reinforced brittle matrix composites with "weak" interface bonding ) and the following conclusions were presented from our fracture mechanics studies of some ceramics and ceramic-based composites.The general low of linear-fracture mechanics was applicable for matreials (1) if only the special attention should be paid to the testing. Because the resistance ageinst crack extension in materials (2) is affected by the stress-shielding due to the process zone formed at the crack tip, due to the wake formed along the fracture surface, accurate analysis by non-linear fracture mechanics based on the damage-free crack or notch will be required. For the precise evaluation of mechanical properties for matreials (3), pluralistic analysis under tiesile, compression and shear mode will be indispensable.