Particle Impact Damage in Silicon Nitride.
Annual rept. - Part 3,
SRI INTERNATIONAL MENLO PARK CA
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In the study of fracture in thick silicon nitride plates by particle impact and quasi-static indentation, we used three types of silicon nitride hot pressed, reaction bonded. and oxidized hot pressed. The fracture damage occurred in well-defined progressive stages. For impact loads or quasi-static indentation loads that do not appreciably exceed the flow stress in the silicon nitride, the elastic radial tensile stresses cause ring and Hertzian cone cracks to form. In the dynamic case, the short duration of the tensile pulse restricts the formation of the ring cracks to the vicinity of the maximum contact radius of the impacting particle. In the quasi-static case, the ring cracks form well outside the maximum contact radius, suggesting that the fracture nucleation and growth kinetics play a significant role in determining the extent of damage. For dynamic loads that exceed the flow stress of the silicon nitride, the plastic flow reduces the tensile radial stress and produces tensile hoop stresses, which in turn, cause radial cracks to form and propagate. At still higher dynamic loads, lateral cracks form. The intersection of these later-stage cracks with the free surface causes material removal erosion.
- Ceramics, Refractories and Glass