Hertzian contact fatigue on alumina/alumina-zirconia laminated composites

The Hertzian contact fatigue of two Al2O3/Al2O3-ZrO2 laminated composites with different layer thickness and, consequently, different residual stress at the surface, was studied both under cyclic loading and under static loading (stress corrosion cracking). The apparition of a superficial ring crack, considered as the first stage of damage, was recorded as a function of time or number of cycles. A monolithic alumina processed in a similar way than the composites and with comparable microstructure was also tested for comparison purposes. Results show that the laminated composites present better resistance to contact fatigue than monolithic alumina. Comparison between static and cyclic loading data reveals that the alumina suffers from fatigue, and not only from stress corrosion cracking under cyclic loading. This fatigue is attributed to grain bridging degradation of alumina. A simple relationship between indentation load and time for apparition of ring crack, based on the Paris law, is derived, yielding values of the exponents similar to values previously reported in the literature.