Microstructural influences on fatigue crack initiation and early growth behaviour in plain bearing Al-based linings

Fatigue initiation and subsequent short and long crack growth has been investigated in an typical automotive bearing system, focussing on the behaviour of the aluminium-tin-silicon lining material. Crack initiation appears to be associated with decohesion of the interface between the primary, globular silicon and the aluminium matrix. Short crack growth, and crack growth at low Delta K levels in the long crack case, appears to be tortuous and highly microstructurally dependent, deviating towards secondary phase/matrix interfaces. At higher Delta K levels crack growth occurs principally through the aluminium matrix, and classical striations are seen. Multiple crack initiation is seen in the multiphase bearing lining material and crack coalescence gives rise to the dominant crack. Uncoalesced cracks appear to arrest at a "critical" surface crack length, whose dimension has been linked to sub-surface crack deflection within the lining material once the crack reaches the steel backing