Analysis of friction influence on material deformation under biaxial compression state T. Fras a,n , A. Rusinek b , R.B. Pęcherski c , R. Bernier b , T. Jankowiak d a French-German Research Institute of Saint-Louis (ISL), 5 rue du Général Cassagnou, 68301 Saint-Louis, France b Laboratory of Mechanics, Biomechanics, Polymers and Structures (LaBPS), National Engineering School of Metz (ENIM), Route d’Ars Laquenexy, 57000 Metz, France c Department of Strength and Fatigue of Materials and Structures, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Cracow, Poland d Institute of Structural Engineering, Poznan University of Technology, Piotrowo 5, 60-965 Poznan, Poland article info Article history: Received 24 March 2014 Received in revised form 11 June 2014 Accepted 24 June 2014 Available online 30 June 2014 Keywords: Biaxial compression Friction modelling OFHC copper abstract The biaxial compression test, based on the concept presented in [1] and on the technique of the channel- die test [2,3], is discussed as an experimental method allowing evolution of the friction conditions from the dry-film lubrication, by using MoS 2 grease, to the dry conditions to be analysed. This article gives an outline of the experimental set-up, its validation and the technique of the test results analysis. The analysis of friction is based on the experimental data coupled with the numerical simulation of the performed tests and on the theoretical approach introduced in [4]. The Oxygen-Free High Conductivity (OFHC) copper in the ‘as-received’ state in contact with the 42CrMo4 steel are chosen as the materials used for the experimental investigation. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction The behaviour of two sliding surfaces in contact with each other has been a matter of interest since, at least, the Renaissance. Indeed, the first written analysis relative to this topic dates back to that time [5] (notebooks and manuscripts by Leonardo da Vinci (1452–1519)). Friction, wear and lubrication (i.e. the general aspects of tribology) were and still are subjects of investigation for ancient and modern engineers, scientists, sportsmen; and are also part of our everyday life. Friction is sometimes of crucial importance (e.g. walking, brakes, materials processing); however, its influence can also have negative effects which can be reduced by the application of lubricants (e.g. metal manufacturing processes). The influence of friction on the deformation of metals is the subject of extensive studies in many scientific topics covering the fields of wear [6,7], tribology [8,9], mechanics of materials [4,10] or metal forming [11,12], including Severe Plastic Deformation (SPD) techniques [13,14], such as Equal Channel Angular Extrusion (ECAE) [15,16] or High-Pressure Tube Twisting [17,18]. In the above-mentioned fields and many other scientific and industrial applications the direct contact between surfaces at high pressure application leads to a considerable increase in the friction force, which may have undesired effects. Therefore, the understanding of friction behaviour is essential for the design of processes and machines. The concept of friction can be defined as the resistance to motion of bodies that are in contact with each other [19–21]. The friction force F μ is a lateral force which must be overcome so that a body in contact with another body can slide over the latter. Coulomb’s friction law is the basis for the formally accepted definition for the friction coefficient [22], given here in Eq. (1) [21]. It is suitable for the two regimes of dry friction, i.e. static friction between non-moving surfaces and kinetic friction between moving surfaces: F μ ¼ μ U F N ð1Þ where F μ is the friction force acting upon the contact surface, μ is the coefficient of friction and F N is the force normal to the interface between the sliding bodies. The dimensionless quantity known as the friction coefficient μ is an empirical property which is material- and system-dependent [23–26]. This statement means the friction coefficient is not only a property of the pair of materials in contact, but that it also depends on the tribological system [24] considered: materials, coating, lubricant, surface roughness, the materials oxidation, relative sliding speed, sliding mode (unidirectional, reciprocating, multidirectional), duty cycle (continuous contact, intermittent contact), environment, temperature, humidity and atmosphere (air, exhaust gases, vacuum) [23–27]. So many factors have an influence on friction in a variety of different, physical situations Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/triboint Tribology International http://dx.doi.org/10.1016/j.triboint.2014.06.019 0301-679X/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: teresa.fras@isl.eu (T. Fras). Tribology International 80 (2014) 14–24