Methodology for the determination of wheel-roller friction coefficient on 1/5 scaled test rig

Railway technology is strongly influenced by the friction coefficient between wheel and rail. Friction plays a key role in many aspects of railway dynamic such as derailment, wear, noise, stability and is the most important factor to be considered in traction and braking problems. The existing methods for the estimation of maximum adhesion between wheels and rails have some limits due to complexity of adhesion phenomena. Usually, those methods use a criterion such as “adhesion coefficient” to investigate the behavior of the mechanical system for the tractive and braking modes of rail vehicle dynamics. This coefficient also can be connected with slip-friction coefficient because both tractive and braking modes of railway vehicles are modeled as the rolling mode with a slip. It is necessary to say that the maximum value of slip-friction coefficient is higher than adhesion coefficient for the same contact conditions, because the slip-friction coefficient only depends on the physical state of surfaces, while the adhesion coefficient depends also on construction characteristics of rail tracks and railway vehicles. As well-known, to model static friction in the equation giving the condition necessary to initiate slip at a contact, friction force should be less than the coefficient of static friction multiplied by wheel load. In the present work, starting from these mathematical models [1,2,3,4,5], a laboratory methodology for the estimation ofthe value of static friction coefficient by means of experimental investigation is proposed.