Wear 271 (2011) 2640–2650 Contents lists available at ScienceDirect Wear j o ur nal ho me p age: www.elsevier.com/locate/wear Investigation of the dynamic response in a dry friction process using a rotating stick–slip tester P.D. Neis a,∗ , P. De Baets b , W. Ost b , Y. Perez Delgado b , M. Loccufier c , F. Al-Bender d , N.F. Ferreira a , F.J. Lorini a a Universidade Federal do Rio Grande do Sul, Sarmento Leite 425, Porto Alegre 90050-170, Brazil b University of Ghent, Sint Pieterstnieuwstraat 41, Ghent B9000, Belgium c University of Ghent, Technologuepark 914, Zwijnaarde B9052, Belgium d Catholic University of Leuven, Celestijnenlaan 300b, Heverlee B3001, Belgium a r t i c l e i n f o Article history: Received 1 September 2010 Received in revised form 21 November 2010 Accepted 23 November 2010 Keywords: Brake Computational modelling Stick–slip Vibration a b s t r a c t In this paper, the friction stability of brake materials is investigated by means of a rotating stick–slip tester. Experimental results are compared with a computational model implemented in Simulink. The main goal of this work is to find out how vibrations induced by friction are related to mechanical system parameters such as inertia (mass), stiffness, damping and sliding speed. At the same time, a computa- tional model is developed in order to analyse the dynamic response of a dry friction process at different conditions. A friction sample with nominal contact area of 254 mm 2 was subjected to sliding against a gray cast iron disk. The sliding speed was varied between 0.28 and 10 mm/s, while the normal load was kept constant (400 N, equivalent nominal pressure 1.57 MPa). Moreover, tests were carried out in three different damping values and two different stiffnesses. Experimental results show typical stick–slip behaviour for the lowest speeds while for the highest speeds stick–slip disappears and smooth sliding prevails. The computational model can be used to evaluate the dynamic response in dry friction process, as far as static/dynamic coefficient of friction of the mating materials are known as well as the mechanical characteristics of the system. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Despite the high technology aggregate and technological advances of the recent decades in the automotive industry the design of new friction materials, brake linings and pads, is a con- stant challenge yet. More than 2000 different ingredients and their variants are now used to make a commercial brake component [1]. As a part of a commercial truck or automobile, brake materials have additional requirements, like resistance to corrosion, light weight, long life, low noise, stable friction, low wear rate, and acceptable cost vs. performance [1,2]. A good friction material for use in auto- motive brakes must have a stable coefficient of friction over time under a wide range of temperature, contact pressure and velocity [3]. Thus, friction-induced vibration, such as stick–slip or harmonic oscillations [4,5] must be avoided during braking. Furthermore, recent studies show that high levels of vibration cause acoustic and vibrational discomfort to the drivers and besides ruins the service life of many vehicle components [6,7]. ∗ Corresponding author. Tel.: +55 513308 3567; fax: +55 513308 3355. E-mail address: engmecpatric@yahoo.com.br (P.D. Neis). Stick–slip is a process where both stick and slip episodes alter- nate during the friction process between two materials and as a result the coefficient of friction continuously varies between a static (stick phase) and a dynamic (slip phase) value. During the stick phase relative velocity between the slider(s) and disk is null [7,8]. During the slip phase, both relative velocity and friction force vary in a relatively short period of time. Two different shapes for the fric- tion force vs. relative velocity curves (Fig. 1) can commonly occur, namely loops clockwise and counter-clockwise loops [9]. A critical sliding speed exists above which the stick–slip ceases [10]. Sliding oscillations (also called harmonic oscillations) occur when the relative velocity V rel between the friction pair varies between positive and negative values or only between positive values and there is no sticking period (V rel = 0) during the friction process. Static coefficient of friction does not occur during har- monic oscillations. The main vibration frequency is very close to the damped natural frequency of the mechanical system during sliding oscillations and it does not depend on the applied sliding speed. In addition, variations in the coefficient of friction are less significant during sliding oscillations than in stick–slip motion [8]. The occurrence of friction instabilities, such as stick–slip or harmonic sliding, depends on the sliding speed, contact pres- sure, mechanical system characteristics (inertia, stiffness and 0043-1648/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2010.11.022