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Effect of brass in brake pad composites on mechanical, thermal properties and tribo-performance

type de publication      communication nationale avec actes publiés
date de publication 2013
auteur(s) Eddoumy Fatima; Kasem Haytam; Dufrenoy Philippe; Celis Jean-Pierre; Desplanques Yannick
  
conférence 25e Journées Internationales Francophones de Tribologie, JIFT2013
     dates de 29-05-2013 à 31-05-2013
     lieu Lyon, France
     nom des actes JIFT 2013
  
résumé Brake pad materials for automobile applications are basically polymer matrix composites. Various reinforcing constituents used in brake pads are organic, metallic and ceramic fillers which play among others an important role on the mechanical and thermal properties, and the wear resistance at high temperature. Friction and wear depend on various parameters such as the micro-chemical structure of the pad and of the metallic counter-face, the rotation speed, the pressure, and the contact surface temperature [1]. This latter parameter can be locally as high as 600 up to 1,500 °C depending on the brake type [1, 2]. Thermal models have been developed to study interface effects at contacting surfaces [3]. Frictional energy can be dissipated through different mechanisms such as oxidation, rise in temperature, formation of wear particles, entropy changes associated to viscoelastic and viscoplastic deformation, and noise generation [4]. Studies of friction brake show that more than 95 % of the dissipated energy is transformed into heat [3, 5]. Thermal analysis is therefore a primordial step in the study of brake systems since it provides thermo-mechanical properties [3]. The influence of the addition of metallic fibers on the performance of organic friction composites has been investigated using friction tests [6]. Benefits or limitations of the different fibers have been reported, however the issues of thermo-mechanical properties or effect of temperature on friction and wear behavior were not yet investigated [7]. No effort was done to correlate the thermo-mechanical and thermal properties with the friction and wear behavior. An important prerequisite is to get a good understanding on how brake materials behave. However, a link between thermal transitions and tribological behavior occurring at different temperatures is still missing. This investigation is focused on the effect of thermal properties of brass-free and brass containing brake pad composites on their friction and wear behavior to analyze the benefit of brass addition. Hereto, the impact of the incorporation of brass into the composites on their degradation was determined from TGA measurements. In a second step, heat transfer and thermal diffusivity were determined with hot disk to study the effect of brass on the thermal transport properties of brake pad composites. Friction and wear behavior were investigated under reciprocating sliding performed at room temperature (RT) up to 400 °C. The coefficient of friction and the dissipated energy were analyzed for both brass-free and brass containing composites. The observation of the wear track enabled us to suggest a possible relationship between the thermal and mechanical properties on one side, and the friction and wear behavior on the other side. TGA results indicate that thermal decomposition pathway of the brass-free composite and one containing brass are quite similar. Hot disk measurements showed that the heat transfer significantly improved in the presence of brass. However, the presence of brass induces a significant decrease of the storage modulus of the composite. Experimental results obtained show that brass particles decrease the wear resistance of the composite at room temperature. In an attempt to establish how the brass acts positively on the friction and wear performance of brake pad materials, the microstructure before, during and after sliding tests was investigated. A poor interaction was observed between brass and matrix what probably leads to a reduction of friction and wear resistance at room temperature. At higher temperature, brass containing composite exhibits a lower wear track depth. The enhancement of wear resistance of the brass containing composite was attributed to the better heat transfer in comparison with a brass-free composite.
mots clés Sliding wear, polymer-matrix composite, brake materials
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