Fracture mechanisms of the SCS-6 fiber-reinforced titanium alloy matrix composites: Jeng, S. Diss. Abstr. Int. June 1992 52, (12), 198 pp

Abstract

A finite element study was performed of driving forces of short cracks at inclusions in bearing steel exposed to rolling contact load. Five inclusion configurations were considered, namely a pore, a manganese sulphide 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. Short cracks were allowed to grow from the inclusions. The inclusions were 20 μm in diameter. The cracks were allowed to grow from 2 μm up to 8 μm, away from the inclusion interface into the matrix. The cracks were oriented 45° to the rolling contact plane in agreement with the experimental observations of so-called butterfly cracks in bearing steels. The inclusions had different coefficients of thermal expansion than the matrix. This generated residual stresses during quenching corresponding to a hardening operation of the steel. Friction was taken into account on the crack faces and on the inclusion interface. The material was modelled as elastic. The driving forces of the cracks were studied in terms of crack-tip displacements and energy release rates. The ranges of energy release rates for the very shortest cracks were highest for the through-cracked alumina inclusion followed by the titanium nitride, the pore and finally the manganese sulphide inclusion and the debonding non-cracked alumina inclusion. If early crack growth controls fatigue life a danger index for these inclusions would fall in that order provided the inclusions all have the same size.