Test method A novel method for contact analysis of rubber and various surfaces using micro-computerized-tomography Andr  as Kriston a, b , Tibor Fül € op a , Nihat Ali Isitman a, * , Ond  rej Kotecký a , Ari J. Tuononen b a Goodyear S.A. Colmar-Berg, L-7750, Luxembourg b Department of Mechanical Engineering, Aalto University, Espoo, 00076, Finland article info Article history: Received 5 April 2016 Accepted 21 May 2016 Available online 24 May 2016 Keywords: Contact Micro-computerized-tomography Rubber Image analysis abstract The experimental analysis of the contact state in a tribosystem is of great importance in the study of contact mechanics. In order to make a realistic analysis on the micro scale, it is desirable to keep the tribosystem unperturbed, i.e., without any surface treatment or incorporation of a third body to facilitate the analysis. This study presents the use of a novel technique, micro-computerized tomography (micro- CT), in the investigation of contact between rubber compounds and various counter-surfaces. The goal of this study was to further advance the use of micro-CT in contact mechanics. Specific image analysis techniques were developed in order to process micro-CT images of contact pairs formed by rubber compounds of different hardness levels against counter-surfaces with varying surface roughness and mechanical properties. The micro-CT method has been shown to allow the direct visualization and precise quantification of the real area of contact without altering the original characteristics of the contact pair. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction The Real Area of Contact (RAC) is a widely used characteristic in tribology. Although other, more readily accessible measures such as the nominal or apparent contact area are also popular, they are often not sufficient to fully describe real tribosystems. Practically, all tribological phenomena occur where the tribo-pairs are truly in contact. This area is generally only a fraction of the nominal contact area and its quantification is essential for the correct understanding of the physics of contact. This also holds for the different rubber- counter-surface contact problems. Knowledge of the RAC be- tween the rubber and the road surface is essential for the under- standing of processes such as friction or wear [1,2]. Knowledge of the micro-roughness of rubber seals has a similar importance in the determination of their leak rate [3]. Unfortunately, the precise quantification of the number and size of real contact points is usually not straightforward. The current standard industrial and academic practice for measuring RAC is mostly based on the use of pressure-sensitive films [4e7]. Their principal drawback, besides some limitation in terms of resolution, is that they introduce an additional component into the tribosys- tem. It is highly likely that the presence of the pressure-sensitive film has an undesired impact on the contact conditions. Several efforts have been reported in the literature that attempted to develop alternative methods which are able to bypass the restrictions linked to the use of pressure-sensitive films. Sharma and Pandey gave a comprehensive summary of earlier at- tempts, such as imprinting and painting [8]. Another important family of methods relies on the use of at least one transparent contacting body. Dietrich and Kilgore reported microscope-based methods to study frictional contacts through transparent counter- surfaces [9]. More recently, Lorenz [10] used transparent rubber to observe the changes in the RAC with applied normal pressure, a method which can be considered practical for qualitative contact visualization but less effective for quantitative estimation. An experimental investigation that was more suited to quantifying the RAC was reported by Matsuda et al. [11] who used a digital camera to study a rubber block with a wavy surface pressed against a flat transparent counter-surface. In the work of Eguchi et al. [12] the stick-slip regions between rough rubber hemispheres and glass plates were studied by means of white light interferometry. Larger systems have also been evaluated. Castillo et al. [13] investigated the shape of the contact patch and pressure distribu- tion of a tire on transparent glass using an optical system in which * Corresponding author. E-mail address: nihat_isitman@goodyear.com (N.A. Isitman). Contents lists available at ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest http://dx.doi.org/10.1016/j.polymertesting.2016.05.019 0142-9418/© 2016 Elsevier Ltd. All rights reserved. Polymer Testing 53 (2016) 132e142