Analysis of contact and bending stiffness for Curvic couplings considering contact angle and surface roughness

This paper develops a method for calculating the contact and bending stiffness of a Curvic coupling, and investigates stiffness changes according to the coupling shape and surface roughness characteristics. The surface of the on-site Curvic coupling is chosen as reference for a most accurate simulation. The three parameters representing the surface roughness characteristics—the standard deviation of the asperity height distribution, the average radius of asperities, and the density of asperity on the nominal contact area—are calculated with a profile of the coupling surface through a random process: the contact problem between rough surfaces is tackled using the Greenwood-Williamson model, the Curvic coupling is modeled assuming that it has as many teeth as possible within the machining limits depending on the contact angle, and the tangential stiffness resulting from the contact angle is calculated by dividing into the stick and slip regions, and is taken into account in terms of total stiffness. With this, results showed that using Curvic couplings reduces stiffness than using flat disc couplings because of the contact angle, and that the standard deviation of rough surface height is the most crucial surface parameter affecting stiffness.

Modeling and prediction of the running-in behavior of the piston ring pack system based on the stochastic surface roughness

This paper proposes an efficient numerical approach to predict the initial running-in process of piston ring pack/cylinder liner system. A combined mixed lubrication and wear model coupled with an oil transport model was developed. In order to predict the hydrodynamic pressure efficiently, two improved methodologies, including the Fischer-Burmsister-Newton-Schur (FBNS) approach and the Grid Refinement (GR) strategy, were adopted. Meanwhile, in order to take into account the effect of skewness, Weibull distribution function was adopted to characterize the asperity height distribution. Predicting the wear of cylinder liner was based on the Archard's wear law. The influences of asperity plastic deformation and wear on asperity height distribution were considered. The results show that the developed model can well predict the initial running-in behavior of piston ring pack/cylinder liner system under an engine-like condition.

Studies of Low-loading Micro-slip Contacts on Rough Surfaces with GW Model

Lateral loading and interfacial slip of multi-asperity (i.e., rough) elastic contacts are studied for micro-slip contact conditions. The Mindlin micro-slip model for smooth surfaces is generalized to rough surface contacts using the Greenwood–Williamson (GW) approach, and the general relations of lateral contact force and related stiffness are obtained. The method extends previous approaches by incorporating micro-slip, allowing application to rough surfaces and providing simple expressions for experimental analysis by use of the Greenwood–Williams roughness parameters. As applications, the numerical results of micro-slip contacts on rough surfaces for Gaussian and exponential asperity height distributions, respectively, are obtained based on the general relations of the extended model, and are compared and discussed for low load cases.