| Typical friction material is constructed by for parts, the binder, reforcement materials, filler and fricition additive materials, and made use of the advantage of fiber, miner and lubrications.The binders including phenolic (PF), benzoxazine (BZ) and nitrile (NBR) are studied in this paper. The effects of glass-to-rubber transition of resin matrix on the friction and wear characteristics of friction materials is examined, in relation to different types of thermosetting resins and blend resins.Tribological and thermal behavior of both micrometer-sized ceramic fiber and nanometer-sized potassium titanate whisker (PTV) reinforced automotive brake linings were investigated. The glass fiber, copper fiber, mineral fiber, Kevlar, potassium titanate whisker and vermiculite were used to prepare the multi-reinforced non-asbestos organic (NAO) automotive friction materials. The multi-reinforced materials have the various characters of micro and nano sized structures, one and two dimensions, inorganic and organic natures. The mechanical and friction properties of the automotive friction material were investigated to optimize the experimental condition. It is important to emphasize that the friction performances were studied under the application condition. The reinforcing mechanism was discussed based on the environment scanning electron microscopy observation.In the present work, nano ZrO2reinforced polybenzoxazine composites were produced. The friction behaviors of ZrO2-polybenzoxazine nanocomposites were evaluated on a Chase Friction Material Test Machine. An attempt was made to examine the effects of the glass-to-rubber transition on the friction and wear characteristics of ZrO2reinforced polybenzoxazine nanocomposites, in relation to the content of zirconium oxide. The thermal and tribological properties of the nanocomposites were measured by dynamic mechanical thermal analysis (DMA) and friction test, respectively. In addition, the friction mechanism of the nanocomposites were proposed based on the experimental and reference results.A high lever of firciont coefficient of frcion material is perfered. As result, materials such as SiO2, Al2O3, ZrSiO4and MgO were used to improve the firciont coefficient. To further improve the the fricion properties, the friction and wear behavior of friction materials filled with irregular and spherical silica particles is discussed in this paper. In addition, surface treated spherical silica powders were prepared and used as fillers to improve tribological properties of friction materials. Friction coefficient and wear tests in a DSM constant-speed tester were carried out and followed by SEM observations.Using dynamic finite simulations we investigate how the friction coefficient depends on the sliding speed. The load dependent model we developed is corresponds to common friction systems, which is based on the constant load where the friction couples are sliding under fixed load for various speeds. Here we study the effect of the sliding speed on the contact distance between two contacting bodies. By investigating the energy dissipation of the contact bodies during the sliding process, we show how the friction coefficient is affected by the sliding speed.Deatails are given follows:(1) The effects of the glass-to-rubber transition of resin matrices on the friction and wear characteristics of friction materials were investigated. Pure and blend thermosetting resins were examined in the paper. The experimental results revealed that adding PF resin and rubber could lower the curing temperature and improve glass transition temperature of BZ resin. Correspondingly, the increasing temperature and broadening width of tan5peaks for P-B-N resin based friction materials were owing to relatively stronger intermolecular interactions between relatively complete polymer crosslinking network and fibers and other ingredients. P-B-N based friction material occupied relatively higher glass-rubber transition temperature, resulting in better ability to stabilize the friction coefficient and wear rate under relatively higher braking temperature.(2) Multi-reinforced NAO automotive friction material has the various characters of micro and nano sized structures, one and two dimensions, inorganic and organic natures. The multi-reinforced material under the optimized condition possesses higher impact strength, better wear resistance and friction stability, resulting from the mix and synergistic effect of various reinforced materials. The results revealed that combined fiber-reinforced materials had higher impact strength, friction stability, and wear resistance than those with only one type of fiber.(3) Additing small amount of nano ZrO2increase the storage modulus and Tg values of the ZrO2-BZ nanocomposites, due to the exceptional mechanical strength of ZrO2particles and the interfacial adhesion between ZrO2and polymer to restrict the segmental motion of polymer. Comparable to the pure resin, the nanocomposites possessed relatively higher COF values with the increase of applied pressure under varying temperatures, which was resulted from the reinforcement of ZrO2resulting in the increased storage modulus and glass transition temperature. The nanocompistes containing4wt%ZrO2occupied relatively higher modulus and glass-rubber transition temperature, resulting in better capability to stabilize the friction coefficient and wear rate under the applied conditions. The results also revealed that the temperature and load sensitivity of nanocomposites increased with the increasing of load and temperature. This behavior was speculated to be due to the effect of the temperature dependence of modulus in the surface topography and strength. But speed sensitivity varies with the temperature, due to the effect of temperature dependence of viscoelastic response in the energy dissipation.(4) Compared to irregular silica, the spherical silica powders could improve the wear resistance but decrease the friction coefficient. The surface treated spherical silica powder is more effective in the improvement of the wear resistance, fade and recovery properties, but with the similar friction coefficient of irregular silica filled materials. This makes it possible to be used as friction-improving fillers in brake materials. Mechanisms for the improvement are also discussed in this paper.(5) Using dynamic finite simulations, we developed a load dependent model which is corresponds to common friction systems, and based on the constant load where the friction couples are sliding under fixed load for various speeds. The contact distance increased with the sliding speed. An increase of the sliding speed also leads to a decrease in the polymer chains response time to the contact stress and the increase in storage moduli. The dependence of the reaction force on sliding speed can be rationalized by assuming that the frequency dependence of the polymer chains relaxation times is affected by the damping effects of contact stress. The deformation volume and relaxation times decreased with the increase of the sliding speed, which result in the decrease of energy dissipation. |
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