Nonlinear numerical model for predicting charge conditions on rolling bearings submitted to environmental vibrations

During, last decades the power increasing of mechanical systems and the request for increasing service life leads mechanical components of a system to work in extreme conditions. In particular actual mechanical systems include surfaces in sliding contact that are subjected to wear if exposed to high vibration. In fact, the vibration of components in contact results ill large oscillations of the local contact stresses, due to the local deformation of the components at the contact interfaces. Thus the necessity to approach an interdisciplinary problem dealing with dynamics (system vibrations) and tribology (contact behavior). This paper presents an analysis concerning the influence of the vibrations induced by aircraft engines oil the wear of contact surfaces of rolling bearings of the bleed system valves. The study is developed on the framework of an European project. To study the wear. resulting of fretting and false Brinelling known to occur in quasi-static assemblies in vibratory environment, at the contact surfaces between balls and rings of the valve bearings it is then necessary to achieve the forces dues to the system vibrations and acting at the bearings connections with the structure. In order to perform a numerical transient analysis of the system dynamics a nonlinear simplified model of the valve is developed. The model includes the stiffness of the preloading springs, the nonlinearity of the bearings stiffness and the nonlinearity due to the possible detachments and impacts between the bearings and the frame of the valve. The input of the models is the induced vibrations by the aircraft engine. The outputs are the relative vibration between the frame of the valve and the shaft charring the butterfly, which corresponds to the relative displacements between the outer and the inner rings of the bearings (the bearings are sited between these two components) and the time behaviour of the forces between the bearings and the frame of the valve.. The model is validated by comparing the numerical results of the relative displacement with experimental results from vibration tests carried out on valve assembly. The time behaviour of the forces and the respective displacements between the contact surfaces, achieved with the presented analysis, will be the inputs for a Finite Element Model developed to reproduce and analyze the local contact constraints