Residual Stresses in Rotating Steel Cylinders with Composite Surface Layers

After undergoing a manufacturing process, materials may exhibit internal stresses referred to as residual stresses. In steel-composite hybrid structures, residual stresses are typically formed due to the unequal thermal behaviour of the steel and composite. Thus, knowledge of the residual stress state is important in the assessment of the external-internal loading in steel-composite hybrid structures. This thesis primarily focuses on estimating the criticality of the residual stress state in a paper machine roll structure consisting of a steel cylinder and glass fibre reinforced epoxy composite surface layers. Of special interest is evaluating the bond between the cylinder and surface layers with different surface layer edge geometries by studying stress and crack tip loading levels. A secondary aim is to provide an extensive overview of the physical background of residual stress formation and special characteristics of residual stress numerical simulations and related material modelling. Numerical simulation models introduced in this study were employed to evaluate the residual stress state and its effects in the roll structure. The scope of the simulations was limited to thermal residual stresses during the cool-down phase. The emerging stress state was not found to be critical as regards the cohesive strength of surface layers. However, the bond between the cylinder and associated surface layer was evaluated as being critical in the event of an initial flaw. Thus, a crack in the bond edge may grow due to the loading induced by the residual stresses. Cylinder rotation was found to have no significant effect on the crack tip loading and a nip effect was shown not to increase the crack tip loading criticality near the nip contact area. Experimental methods could prove useful in creating more precise material models and improving simulation accuracy. In addition, the obtained simulation results for residual stress levels and crack tip loading could be validated experimentally.