【作者】 叶伟；

【导师】 马云海；

【作者基本信息】 吉林大学 ， 农业机械化工程， 2011， 硕士

【摘要】 本研究瞄准汽车摩擦制动材料的现状和发展趋势,考虑到黄麻纤维、竹纤维和羊毛纤维性能各有其优点,并兼顾到材料的性能和经济性,采用纤维表面改性方法,开发一种绿色、节能的天然生物纤维增强摩擦材料,为高性能汽车制动摩擦材料制品研制奠定技术基础。本文对黄麻纤维、竹纤维和羊毛的表面进行了改性处理。利用单因素试验设计方法,对天然生物纤维增强摩擦材料进行摩擦磨损试验,得到了摩擦材料的摩擦因数和磨损率的变化规律,并对摩擦材料的磨损形貌进行了观察分析。通过对黄麻纤维、竹纤维和羊毛纤维结构观察分析发现,黄麻纤维具有内层中空结构,可以减低摩擦材料表面的磨粒磨损。在抱合力的作用下,竹纤维集合体中纤维相互纠缠、粘结、钩挂而抱成一团,不易松散。羊毛纤维具有天然卷曲,整体外观为覆盖有鳞片状结构的圆柱体。这种特殊结构使得羊毛纤维可以和其他的填料充分混合。对天然生物纤维增强摩擦材料进行摩擦磨损试验。结果表明,在升温条件下,不同含量的黄麻纤维和羊毛纤维增强摩擦材料摩擦因数均高于无黄麻纤维和羊毛纤维增强摩擦材料的摩擦因数。不同含量的竹纤维增强摩擦材料摩擦因数均低于无竹纤维增强摩擦材料的摩擦因数。在降温条件下,黄麻纤维、竹纤维和羊毛纤维增强摩擦材料的摩擦因数是随着温度降低而呈下降趋势。在250℃左右,三种纤维增强摩擦材料的摩擦因数均出现不同程度的波动,12wt.%黄麻纤维增强摩擦材料,12wt.%竹纤维,0wt.%和4wt.%的羊毛纤维增强摩擦材料的磨损率最大。对三种天然生物增强摩擦材料的磨损率和摩擦因数进行对比,结果表明在350℃条件下,9wt.%黄麻纤维增强摩擦材料、3wt.%竹纤维增强摩擦材料和3wt.%羊毛纤维增强摩擦材料均具有相对较好的摩擦性能,3wt.%羊毛纤维增强摩擦材料的磨损率最低为0.4938331×10-7cm3N-1m-1。对上述三种天然生物纤维增强摩擦材料的表面形貌和磨损机理进行了分析后发现,天然生物纤维增强摩擦材料的磨损形式主要是黏着磨损和磨粒磨损。在天然生物纤维增强摩擦材料的磨损表面存在着孔隙,表面孔隙使摩擦表面材料与空气中的氧气接触较多,碳质材料与氧气发生固-气相反应。孔隙越多,氧气分子越容易扩散进去,产生的磨粒更容易被氧化。同时减小了摩擦表面的磨粒数量,降低了磨损率。对盘式制动摩擦材料制动过程进行了温度场模拟分析。结果表明,汽车制动过程是将动能与势能转化为热能而耗散的过程,对偶件接触面的热应力分布不均,在滑动摩擦过程中,接触面相当于接受定热源作用,接触区温度逐渐上升,最高温度在接触面中线附近并向外扩展,温度从接触面向四周呈递减趋势,且温度梯度越来越小。而且接触压力分布和温度分布是相互耦合的。压力分布影响对偶件的温度分布,而对偶件的温度分布的局部特征又反过来影响到界面的压力分布。这是导致制动器的磨损以及产生摩擦噪声的主要原因。如果由于制动器的设计不合理,使得热应力无法均匀作用在摩擦块上,严重时很容易导致摩擦块磨损和断裂。更多还原

【Abstract】 According to the situation and development trend of friction materials, taking into account properties, merits and the economy of the jute fiber, bamboo fiber and wool fiber of the material, a green, energy-efficient natural biological fibers reinforced friction materials for automotive brake friction materials was investigated by fibers’surface modification in order to establish technological foundation of high-performance products.Friction and wear tests of the natural bio-fiber reinforced friction materials were carried out by using single-factor experiment design friction coefficient and wear rate were measured. The worn morphology of the friction materials were observed and analyzed by scanning electron microscope.The structures of jute fibers, bamboo fibers and wool fibers were observed. Jute fibers with the inner hollow structure can improve the abrasive wear on the surface of the friction materials. Bamboo fibers assembly are entangled, adhesive, hook and hold together and not easy to loose for the role of the cohesion. Wool fibers have a natural curl and are cylinder covered by scales. This made that the process of mixing with other fillers can be fully mixed and entangled and wool fibers are difficult to pull the wool fibers in the friction and wear. The surface layer of the wool fiber is consist of keratinocytes scale-like cell. The wool fibers were evenly distributed among the friction materials and are very good for the combination of fillers and resin.Friction and wear test were done on the samples with natural biological fibers reinforced friction materials. The results showed that the friction coefficients of friction materials reinforced by jute fibers were higher than those of friction materials with free-reinforced by jute fibers during the temperature increase. Jute fiber reinforced friction coefficient of friction material was lower than non-Ma fiber reinforced friction material when the temperature decrease. In the cooling conditions, friction coefficients of friction materials reinforced by the jute fibers, bamboo fibers or wool fibers reduced as the temperature decreased. At about 250℃, the friction coefficients are different degrees of volatility. The wear rates of reinforced friction materials containg 12wt.% jute fibers, 12wt.% bamboo fiber, 0wt.% or 4wt.% the wool fibers were the highest.Wear rate and friction coefficient of friction are compared. under the conditions of 350℃,the results showed that 9wt.% jute fiber reinforced friction material, 3wt.% bamboo fiber reinforced friction materials and 3wt.% wool fiber reinforced friction materials are relatively good friction properties, wear rate of 3wt.% wool fiber reinforced friction material as low as 0.4938331×10-7cm3N-1m-1.Wear mechanism of natural biological fibers reinforced friction materials was analyzed by surface worn morphology obtained by scanning electron microscopy. For the natural biological fiber reinforced friction materials the main wear mechanism is adhesive wear and abrasive wear. Porosity presented in the natural biological fiber-reinforced wear surface of friction materials and pore surface can make the friction surface material contact with more oxygen in the air. Carbon materials act with oxygen in the form of solid-gas phase reaction. The more pores, the easier diffusion of oxygen into the molecule, produced grain more easily oxidized. While the amount of friction abrasive surface reduces, so do the wear rate.The temperature field simulation was carried out by ANSYS finite element for disc brake friction materials during braking. Brake is the process of changing kinetic and potential energy into heat and consumption. Thermal stress on the contact surface of the dual pieces is uneven distribution during the sliding friction process, the contact surface is equivalent to accept the role given heat source, the temperature gradually increased contact area. The highest temperature in the vicinity of the contact surface and the outward expansion of the center line, the temperature for four weeks from exposure showed a decreasing trend, and the temperature gradient smaller and smaller. And the contact pressure distribution and temperature distribution is coupled with each other under. Dual pieces of the pressure distribution of the temperature distribution, and even parts of the local characteristics of temperature distribution in turn affect the interface pressure distribution. This is the result of wear and friction brake vibration and noise of the important reasons. If the brake design is unreasonable, not even making the role of thermal stress on the friction block, severe heat can easily lead to severe wear and fracture of friction block phenomenon.更多还原