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A finite element study was performed on driving forces of short cracks at inclusions in bearing steel exposed to rolling contact load. The inclusions were assumed to be elastic and the steel matrix was elasto-plastic with material parameters from cyclic loading tests. The surface load on the raceway was simulated with a moving Hertzian pressure distribution. An inclusion was situated in the steel below the raceway. Short cracks were allowed to grow from the inclusion between subsequent passages of the contact load. The inclusion had a size of 20νm in diameter. The cracks were oriented 45° to the rolling contact plane. Five inclusion configurations were considered, namely a pore, a manganese sulfide inclusion, a through-cracked alumina inclusion, an alumina inclusion which was uncracked but which could debond from the matrix and finally a titanium nitride inclusion. The driving forces of the cracks were evaluated in terms of energy release rates. The magnitudes of these rates were significantly influenced by inclusion type, crack configuration, crack length, Hertzian loading level and metal plasticity. A ranking list was made of the different inclusions with respect to expected detrimental effect on contact fatigue life.
contact fatigue, steel, inclusion, fracture mechanics, finite element method, plasticity, friction
Professor and Deputy Managing Director, Swedish Institute for Metals Research, Stockholm,