For many years, bearing suppliers have been using the specific pressure to evaluate the fatigue risk of conrod bearings. However, modern engines have made the bearing more sensitive to various phenomena such as the thermal expansion or the elasticity of the conrod housing. These effects modify the stresses in the bearing layers and consequently fatigue risk. In this paper, we propose a new way to determine the bearing fatigue resistance. To achieve that, we analyze the elastic and plastic behavior of the bearing along the engine life. We detail and provide the analytical relationships which determine stresses in the overlay and in the substrate of the bearing in order to analyze their fatigue resistance. Various physical loads are taken into account such as the thermal load, the hydrodynamic pressure field, the fitting load, the free spread load.
A good knowledge of the relationships between those physical phenomena helps to understand the mechanical behavior of the bearing. In particular it allows demonstrating that plastic flow occurs in the substrate and in the overlay during the first combustion cycles and the first thermal cycles. These plastic flows create residual stresses and modify the stress tensor in the different layers. As a consequence, the overlay and substrate layers are subject to high cycle fatigue (H.C.F.) function of engine cycles and low cycle fatigue (L.C.F.) function of thermal loadings. The high cycle fatigue analysis is performed using multiaxial criteria.