The surface and subsurface region of the head of railroad rails are subjected to extremely high and complex loads, leading to large shear strains within some 100 microns near the surface of a rail. The local state in this surface region is strongly influenced by the surface roughness of the rail and wheel, which must be included in the calculation of the local deformation and stress state. This influence is investigated by a two dimensional finite element study. A small part (micro-region) of a wheel is pressed onto a rail. The wheel and the rail are given a measured surface roughness. The wheel is loaded according to the average value of the contact pressure calculated by a three-dimensional finite element model and is made to slide along the rail. Furthermore, metallurgical scanning electron microscope investigations are presented, which characterize this local deformation state in the rail. These results show shear strains of 5 and higher Also cracks along the deformation lines are detected. The large shear strains found by these investigations compare very well to those calculated by the finite element model. Both the metallurgical investigations and the numerical calculations show impressively that the extremely high shear strains near the surface of a rail have to be considered and included in all investigations and models of wear and damage at a rail surface. The main progress applying the finite element model lies in the fact that the development of these extremely high shear strains can be modeled straightforward using very common assumptions about loading, creepage, material and friction coefficient. These results are obtained due to the introduction of an elasto-plastic rough surface contact into the finite element model which is a main improvement in calculating wheel-rail contacts.
Modeling and characterization of large shear strains at a rail surface
Simulation und mikroskopische Untersuchung großer Tangentialverformungen auf der Oberfläche einer Eisenbahnschiene
2003
9 Seiten, 8 Bilder, 31 Quellen
Conference paper
English
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