Mixed-Mode Fracture of Hot-Pressed Si3N4 |
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Authors: | JOHN J PETROVIC |
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Affiliation: | Los Alamos National Laboratory, Los Alamos, New Mexico 87545 |
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Abstract: | The mixed-mode fracture of hot-pressed Si3N4 was investigated using inclined indentation surface flaws in bending and large crack geometries in combined tension/torsion. Non-coplanar fracture was observed in all cases. Values of KIc, KIIc, and KIIIc stress intensity factors were obtained, with ratios KIIc/KIc= 0.79 and KIIIc/KIc= 1.55 observed. For large cracks, mode II conditions had more of an effect on mode I fracture than mode III conditions. The mixed-mode I-II fracture of surface flaws was significantly different from that for large cracks, suggesting surface flaw shear resistance effects. A model describing these effects was derived, based on the ratio of the crack-opening displacement to the crack surface asperity height. |
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