Ceramic contact failure

An interesting variant of contact failure occurs if the contact is near an edge, as the crack may not stop there and an edge flake may break out [33-36]. Such edge flaking can often be observed in ceramic components used, for example, in classical ceramic... 

Ceramics cannot be bolted or riveted the contact stresses would cause brittle failure. Instead, ceramic components are bonded to other ceramic or metal parts by techniques which avoid or minimise stress concentrations. 

The introduction of surface compressive layers can strengthen ceramics and is a well-established technique for glasses (see Sec. 13.5 for more details). The underlying principle is to introduce a state of compressive surface residual stress, the presence of which would inhibit failure from surface flaws since these compressive stresses would have to be overcome before a surface crack could propagate. These compressive stresses have also been shown to enhance thermal shock resistance and contact damage resistance. 

Low resistive cell failure mode. Ceramic is a brittle material and may have a small crack or may break. In this case the liquid salt NaAlCU gets into contact with the liquid sodium (the melting point of sodium is 90 °C) and reacts to salt and aluminum ... 

The failure map for the natural surface cracks was created. The results indicate that it is hard to get failure for ceramics balls when the contact stress is less than a certain value. For example, when the maximum contact stress is less than 5.0 GPa for the turbine oil, and 4.0 GPa for the traction oil, there will be no failure for the natural surface ring cracks in 10 x lO stress cycles. 

The SIF values along the crack front can provide the necessary information to determine whether the ceramic ball would survive or fail. Rolling contact fatigue failure of silicon nitride bearing elements with surface cracks can be predicted using the numerical fracture mechanics analysis. 

M. Hadfield, T. A. Stolarski, R. T. Cundill, and S. Horton, Failure modes of pre-cracked ceramic elements under rolling-contact. Wear, 169 (1993) 69-75. 

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