Optimization of fatigue life of hollow rollers under pure normal loading

Abstract

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.