Porušování jízdní plochy železničních kol

The purpose of the article is to acquaint the technologically oriented public with the causes and laws governing the occurence and development of defects which appear in the form of crumbled spots on the running surface of railway wheels. These defects most likely occur as a result of the existence of initiators in the upper layer of the running surface. The propagation of these defects in the form of oblique cracks in influence especially by the general force effects in the wheel-rail contact area. The slids accompanying this action may be the cause of local martensitic structures (hard spots). Initiators of this type along the circumference of wheel running surface have been metalographically proven. Based upon a numeric calculation, we can presume a strong impact of shear forces in the contact area. As a result of the process of rolling, these forces change the plus-minus sign along contact and cause the asymetric character of radial load related to the contact normal. This proves the incorectness of the idea of so called single zone slid range. Based upon the analysis of stress, provided the formation of plastificated and hardened contact layer, the opinion was uttered on the laws which govern hte considered defect propagation. In the conclusion, the article underlines the necessity of ongoing experiments which have been prepared in the Czech Republic with the help of specifically developed testing equipment