Surface Breaking Crack Influence on Contact Conditions. Role of Interfacial Crack Friction. Theoretical And Experimental Analysis

Abstract

Numerous studies are devoted to the determination of two body contact conditions, i.e the contact area, the stick and slip zone repartition, the normal and tangential pressure distributions. Interfacial roughness, friction, worn profiles for instance are taking into account as they disturb the hertzian stress field, but no specific attention is paid to the influence of surface breaking cracks. The mutual influence of surface breaking cracks on two body rolling contact conditions was studied theoreticalyy in a previous paper by Dubourg and Kalker [1]. Significative overpressure relatively to the classical maximum hertzian pressure and split up of the contact area were obtained numerically. An original experimental simulation is undertaken to validate these results. The theoretical model is the combination of a two body rolling contact model and a fatigue crack model. The steady rolling contact between the wheel and the rail is solved as a unilateral contact problem with friction. Displacement and stress expressions derive from Boussinesq and Cerruti potentials. The fatigue crack model is based on distributions of dislocations for crack modelling and unilateral contact analysis with friction for the contact solution between crack faces. These two problems are solved in turn as displacements generated by cracks modify the two body surface geometry. This process goes on until convergence is reached, i.e when the two body contact conditions are stabilised from one iteration to the next. The experimental work is based on photoelastic technique. Birefringent slabs for both wheel and the cracked rail are employed. Isochromatic fields, normal and tangential loads and global displacements are recorded continuously during the loading. Visualization and calculation of pressure peaks in the wheel and extent of the contact area are performed.