| According to their tribological load collective, both the train wheel steel/rail steel system which has been studied through mechano-rolling fatigue damage tests and the metallic rubbing pairs which have been studied through mechano-sliding fatigue damage tests under the condition of static load with accompanying cyclic impacting load together should belong among "active systems", namely, "mechanical system in which any form of friction process is realized and alternative load is taken up and transmitted through simultaneously". In this case, wear-fatigue is the dominating type of damage in these systems. Their problems are categorized in study of tribo-fatigue which is a "science concerned with wear-fatigue damage and failure of active systems of machines and equipments"The dissertation aims to investigating the interaction between friction phenomena (including rolling friction and sliding friction phenomena) and mechanical fatigue in active systems. Clarifying the rule of such interaction should be helpful for seeking the critical condition of the active systems and the technique for foreseeing the life of the active systems. And as a result, we could develop the theory and method to control and prevent the failure of the active systems running in complex and important machines and equipments.During the study on mechano-rolling fatigue damage of the train wheel steel/rail steel system, the following work were finished and correlative results were got:(1) Three kinds of specimens were made from real train wheel steel and rail steel. The fatigue limit tr.iof the rail steel, the critic contact fatigue pressure Pf of the wheel steel/rail steel system and the mechano-rolling fatigue limit Pfa of the wheel steel/rail steel system were determined respectively by using the were-fatigue test machine. The Pfa of the train wheel steel/rail steel system was measured for the first time in the world. And three fatigue curves were plotted accordingly.(2) It is discovered that when optimum cyclic bending load acts on a rolling rubbing pair, its mechano-rolling fatigue Pfa increases obviously because of the interaction between the cyclic bending stress and the contact stress.(3) Based on the mechano-rolling fatigue damage action, the inferences of the cyclic bending stress on the wear behavior of rolling rubbing pairs were investigated and the mechanism of improving contact fatigue limit of rolling pairs by the optimum cyclic bending stress were discussed preparatively. The microtopography of the surface damage in rolling friction tests and during wear-fatigue tests observed by an atom forcemicroscopy show that in case of pure rolling friction any higher contact pressure intensifies plastic deformation and hence fragmentation of grains, it initiates the appearance of discrete pores and cracks followed by their coalescence into chains. The system of deformed grains, chains of pores and cracks is unidirectional and it is oriented in the direction of rolling. This process produces relatively large discrete pitting. Two types of wear, vis. delaminating and pitting, come to dominate. Similar fragmentation of grains and origination of pores and cracks are observed during wear-fatigue tests. As the amplitude of cyclic stresses increases, the processes of origination of the second system of cracks accelerate and these cracks arrange transverse to the rolling direction. Hence, damage becomes dissipated and an almost regular grid of intersecting cracks and pores appears around finely dispersed particles (fragments of grains) of the material. The stronger the cyclic stresses the denser is the grid of cracks and pores, the finer and thinner the separating particles become. It prevents the appearance of larger pitting and no pits are observed under these conditions. Surface chipping is the dominating wear process in this case. It is characterized by the separation of fine dispersed particles from the working surface.During the study on mechano-sliding fatigue damage of metallic sliding rubbing pairs under the conditi...
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