No abstract

Contact stresses are one of the most important parameters in the analysis of a contact problem found for instance, in the design of gears and roller bearings. In this work the influence of geometrical surface imperfections on the normal pressure distribution in the contact is studied. A variational formulation based on the principle of complementary virtual work is used to solve the normal contact problem. The normal contact between two elastic half-spaces is considered, as the contact surface is small when compared to the dimensions of the contacting bodies. Results are presented to determine the influence of surface roughness, wavelength, and amplitude on the normal pressure distribution.

The late Proterozoic rocks of Central Brittany, represented essentially by Upper Brioverian sediments, are considered to be a late to post-tectonic molasse to the Cadomian chain. The poly-orogenic character (Cadomian and Hercynian) of the deformation structures affecting these rocks is noted from the Baie de Douarnenez to the Rennes region. However, the main syn-metamorphic deformation event is clearly of Hercynian age. Furthermore, we show that this event and the associated metamorphism are directly related to the emplacement of the Hercynian leucogranites. The syntectonic nature of the leucogranites, with respect to the deformation of their envelope, is therefore affirmed and the concept of a 'Brioverian basement', in the mechanical sense of the term and contrasted with a 'Palaeozoic cover', must be abandoned.The greater part of Central Brittany (Fig.

Traction in lubricated elliptical Hertzian contacts with colinear speeds is studied. A method is described to calculate the stresses, temperatures and shear strain rates distribution along and across the film. Visco elasto-plastic behavior of the lubricant, convection, and conduction effects and pressure distributions are taken into account in this method. Elastic energy release is discussed. Shear modulus and limiting shear stresses are determined from experiment by curve fitting. Correlation between theory and experiment is analyzed.

This paper shows that both micropits and spalls occur near pure rolling conditions. The first are initiated at the surface and are related to asperity interaction. The second are well described in the literature and will not be discussed here. A model capable of predicting the mechanical conditions under which micropits are generated is presented. In this model the pressures on asperities are analyzed for given separations of the surfaces; elastic, elasto-plastic, or plastic deformations are deduced. Master curves can be obtained if a pressure index is used, the model requires a comprehensive description of the surface as it calls for the distributions of both profiles height and asperity tip radii of curvature. A new approach was proposed to define the peaks which carries the load in the contact. In this model a peak is defined with respect to the separation of the surfaces. Good correlation between theory and experiment was obtained for materials as different as mild and case hardened steels and with ground and “as received” treated specimen surfaces. The rate of micropit formation which depends necessarily on running-in cannot be predicted at this time. Results however clearly show that when running-in takes place, i.e. when the pressure on asperity tips decreases to a value compatible with elastic deformation, the rate of formation of micropits with time tends to zero and of course fatigue life is increased.