I. Demirci

The Scale Effect of Roughness on Hydrodynamic Contact Friction

Multistage abrasive finishing processes (grinding, polishing, honing, etc.) are commonly used to produce the geometrical properties of a surface to meet its technical functionalities in the operating characteristics of contacting parts in friction, relating to their durability and reliability (running-in performance, wear resistance, load-carrying capacity, etc.). Coarse abrasive grits followed progressively finer ones are used, which leads to a multiscale stratified surface texture. In this article, a numerical model of elastohydrodynamic (EHD) contact coupled to a multiscale surface texture model was developed that allows tracking the scale effect of surface features and their interactions on friction performance and lubricant flow under hydrodynamic lubrication conditions. Because the simulation model has as an input the surface topography and to overcome the variability in surface finish formation, textured surfaces at different stages of the finishing process were simulated (virtual texturing method). Surface topography can be decomposed into two principal components: superficial roughness and valleys. Superficial roughness was modeled using a fractal model and a scaling factor was introduced to model valley patterns. The results show the relationship between friction and surface scales.

Multiscale Analysis of the Roughness Effect on Lubricated Rough Contact

Determining friction is as equally essential as determining the film thickness in the lubricated contact, and is an important research subject. Indeed, reduction of friction in the automotive industry is important for both the minimization of fuel consumption as well as the decrease in the emissions of greenhouse gases. However, the progress in friction reduction has been limited by the difficulty in understanding the mechanism of roughness effects on friction. It was observed that micro-surface geometry or roughness was one of the major factors that affected the friction coefficient. In the present study, a new methodology coupling the multiscale decomposition of the surface and the prediction of the friction coefficient by numerical simulation was developed to understand the influence of the scale of roughness in the friction coefficient. In particular, the real surface decomposed in different roughness scale by multiscale decomposition, based on ridgelets transform, was used as input into the model. This model predicts the effect of scale on mixed elastohydroynamic point contact. The results indicate a good influence of the fine scale of surface roughness on the friction coefficient for full-film lubrication as well as a beginning of improvement for mixed lubrication.

Study on the relevance of some of the description methods for plateau-honed surfaces

Much work has been undertaken in recent years into the determination of a complete parametric description of plateau-honed surfaces with the intention of making a link between the process conditions, the surface topography and the required functional performances. Different advanced techniques (plateau/valleys decomposition using the normalized Abbott–Firestone curve or morphological operators, multiscale decomposition using continuous wavelets transform, etc) were proposed and applied in different studies. This paper re-examines the current state of developments and addresses a discussion on the relevance of the different proposed parameters and characterization methods for plateau-honed surfaces by considering the control loop manufacturing-characterization-function. The relevance of appropriate characterization is demonstrated through two experimental studies. They consider the effect of the most plateau honing process variables (the abrasive grit size and abrasive indentation velocity in finish-honing and the plateau-honing stage duration and pressure) on cylinder liner surface textures and hydrodynamic friction of the ring-pack system.

A pure thermal model to evaluate heat-affected zone when milling E-glass fiber-reinforced polyester composites

This paper aims at investigating the resistance-to-vitrification of glass fiber-reinforced plastics when milling. A three-dimensional thermal model using volumetric heat source with Gaussian distributed cylindrical flux was developed as DFLUX subroutine and implemented into Abaqus/Standard code. The wheel feed was simulated by the source motion at 250 mm min−1 with spindle speeds of 11,460, 15,280, and 19,100 rpm. Milling tests using abrasive wheel with 10 mm in diameter were conducted on the composite specimens of dimensions 100 × 25 × 4 mm3 with fibers oriented both parallel and perpendicular to the milling direction. Four equidistant thermocouples were embedded within the medium plane of the specimen in order to measure the temperature histories. Each series of tests was repeated four times under identical conditions. Predictions confronted to measurements demonstrated the validity of the proposed model. Cutting perpendicular to fibers was found favoring in-depth heat dissipation. However, the fibers a...

Impact of superficial surface texture anisotropy in helical slide and plateau honing on ring-pack performance

The improvement of environment efficiency of automotive internal combustion engine becomes a fundamental objective. The cylinder engine surface texture considerably influences the functional performances of the ring-pack tribo-system. These surfaces are obtained by honing process that was pioneered in the last decade. Several innovative honing techniques were developed resulting in new surface textures with different cross-hatch angle obtained after several stages: the rough and finish honing and final stage. The aim of this study is to investigate the effect of variable cross-hatch angle generated at a final stage. These measured obtained surfaces are measured by a 3D white light interferometer and used as input data of the numerical model to estimate the friction. The results show the importance of this ‘residual’ angle.