Fracture characteristics microcracking

MICROCRACK FORMATION AND FRACTURE CHARACTERISTICS IN GRANITE UNDER SUPERCRITICAL WATER CONDITIONS... 

The trace of the planar central zone of the microcrack-ladder is marked by the presence of negative crystals and inclusions. This characteristic indicates that microcrack-ladders must be related to healed longitudinal fractures. The formation of unhealed microcracks normal to the loading direction (i.e., the rungs of the ladders) can be understood as follows. Undulatory extinction and dislocation microstructures observed within the microcrack-ladders indicate that plasticity is restricted to a narrow zone ( 100 / m wide) within the otherwise-undeformed host crystal. Therefore, the host crystal responded elastically while the load was applied the elastic strain A/// being about 0.5 percent. Now, in the plastic zone of the... 

The mechanical properties of polycrystalline ZnO ceramics are of special importance for their applications as varistors (see Section 1.4.4.1). When a varistor experiences a high-current pulse, the electrical energy is quickly converted to heat. The inertia of the material, which resists its thermal expansion, and the resonances of the resultant elastic waves in the block, may lead to microcracks and finally to mechanical failure [107]. Characteristic values of mechanical properties of ZnO ceramics are 1.2-1.4 MPa m for fracture toughness, and 100-125 MPa for flexural strength. 

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