Fatigue life investigations have been made for cylindrical hollow rollers in pure rolling contact. In addition to normal loading, the rollers have been subjected to tangential loading of 1/3rd the normal load value. Sufficient coefficient of friction has been used to ensure no slipping occurs. Two main models were built with different hollowness percentages to investigate the hollowness percentage that gives the longest fatigue life. The first model consists of two cylindrical rollers of same size, while the second model consists of two rollers of different sizes. Two cases have been studied, when both rollers are hollow and when only one roller is hollow. The stress distribution in the roller body and the resulting deformation has been investigated using the finite element package, ABAQUS. Then the Ioannides-Harris (IH) theory was used to predict the fatigue life of the hollow rollers in pure rolling contact. Investigations have been made for five different materials, CVD 52100, Carburized steel, VIMVAR M50, M50NiL and Induction-hardened steel. It has been found that the optimum hollowness percentage with the longest fatigue life ranges between 50% and 70%. Many factors affect the optimum hollowness percentage, like the kind of the material used for the cylindrical roller, whether the rollers in contact are of the same size or different size and whether the hollow roller is in contact with another hollow roller or in contact with solid roller. At the optimum hollowness percentage, the roller can live hundred times the life of solid roller. So, as the endurance limit of the material increases, as the fatigue life of the rollers increases too. It has been found that cylindrical roller in contact with another identical sized roller has shorter fatigue life than the cylindrical roller in contact with a bigger roller. That might be related to increase the flexibility of the system that acts as a spring mass system and to the increase of the contact surface area. In case of identical sized models, the longest fatigue life achieved was two hollow rollers of 50% percentage of hollowness. When only one roller is hollow, the optimum shifts to 70% percentage of hollowness. For the non identical sized rollers, the optimum is around 50% but when one roller only is hollow, the fatigue life is longer. That might be related to optimum flexibility that gives the longest fatigue life. If the flexibility of the system is very high, the fatigue life of the roller is reduced because of the effect of the bending stresses.
Fatigue life investigations have been made for hollow rollers in pure normal loading. Different hollowness percentages between 20% and 80% have been tested to find the optimum percentage hollowness that gives the longest fatigue life. Two main models were built for this purpose. Model 1 with two identical sized rollers and Model 2 with two non identical sized rollers. In each model, two cases have been studied, when both rollers are hollow and the case when one roller is hollow while the other one is solid. The Ioannides-Harris (IH) theory was used to calculate the relative fatigue life of the hollow rollers with respect to solid rollers under same loading. Investigations have been made for five different materials, CVD 52100, Carburized steel, VIMVAR M50, M50NiL and Induction-hardened steel. The finite element package ABAQUS has been used to study the stress and deformations in the loaded rollers. In general, the optimum hollowness percentage with the longest fatigue life ranges between 60% and 70% based on the kind of the material, whether the rollers are same size or different size and whether both rollers are hollow or only one of them is hollow. Using IH theory for fatigue life calculation resulted in having infinite fatigue life for those rollers made of Induction-hardened steel that relatively has high fatigue limit value. Rollers in the optimum range are flexible enough to get the best redistribution the stress in the contact zone. For models of a hollow cylindrical roller in contact with a solid roller, the optimum hollowness is around 70%. When both cylindrical rollers are hollow, the optimum hollowness decreases to be between 60% and 65%. At the optimum hollowness, small differences in the fatigue life have been found between models of one hollow roller and models of two hollow rollers. Even though, having both rollers hollow means less weight, saving more material and more stability for the system.
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