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carsSAE2009 - Modeling a Slider-Crank Mechanism With Joint...

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2009-01-0403 Modeling a Slider-Crank Mechanism With Joint Wear Saad Mukras, Nathan A. Mauntler, Nam H. Kim, Tony L. Schmitz and W. Gregory Sawyer University of Florida Copyright © 2008 SAE International ABSTRACT The paper presents a study on the prediction of wear for systems in which progressive wear affects the operating conditions responsible for the wear. A simple slider- crank mechanism with wear occurring at one of the joints is used to facilitate the study. For the mentioned mechanism, the joint reaction force responsible for the wear is, itself, affected by the progression of wear. It is postulated that the system dynamics and the wear are coupled and evolved simultaneously. The study involves integrating a dynamic model of the slider-crank mechanism (with an imperfect joint) into a wear prediction procedure. The prediction procedure builds upon a widely used iterative wear scheme. The accuracy of the predictions is validated using results from an actual slider-crank mechanism. INTRODUCTION Clearances at the joints of multibody systems (usually due to manufacturing tolerance) have been noted to affect the performance and service life of mechanical systems. This may be attributed to the increased vibration, excessive wear and dynamic force amplification as discussed by Dubowsky [1]. Due to the significance of the problem, numerous studies have been conducted with the goal of understanding the dynamic response of these systems in the presence of joint clearances [1-16]. These studies have evolve from the analysis of less complex planar multibody systems [1-3, 5-11, 13,14,16] to more complex spatial systems [4, 15] as well as from rigid multibody analysis [1,2,5- 10,12-16] to flexible multibody analysis [3,4,11]. The studies have demonstrated that the presence of clearances alter the response of the system appreciably. Although these studies will go a long way into allowing designers to take into account joint clearance, the findings may be limited to the idealized case in which wear is assumed to be nonexistent. This is contrary to a realistic scenario in which wear is expected to increase the clearance size and thus further alter the system response. This research seeks to address this issue by allowing the joint clearance to vary as dictated by the wear. As a result, the system dynamics will evolves with the wear and this evolution is captured by an integrated model presented in the article. The effect of the wear on the system dynamics and conversely the effect of the evolving dynamics on the wear can then be studied. In the first part of the paper a wear prediction procedure is presented. The procedure presented is based on a widely used finite-element-based iterative wear prediction procedure. In the next part, modeling of a perfect and imperfect joint is discussed. Two different kinds of imperfect joints are discussed. The first being a general imperfect joint model in which the two components of the joint are allowed to move relative to each other depending on the dynamic behavior of the system. The second model is a simplified and more
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