炭/炭复合材料飞机刹车盘表面加工质量对其磨合性能的影响

在mm-1000试验机上对炭／炭复合材料（CCC）飞机刹车盘3组表面粗糙度不同的试样进行刹车模拟试验。以摩擦表面相对作动向运动时，摩擦表面微凸体发生弹－塑性变形、发生磨损进入磨合状态。采用Talysurf-4仪测定了CCC刹车盘磨合前后的表面形貌及其粗糙度，用SEM对磨损表面和磨粒形貌进行了研究。当刹车盘表面波度较小而表面微观粗糙度在Ra=12.5μm时，有利于在摩擦面上形成摩擦膜，使刹车副很快进入磨合状态。使用恰当的加工方法和加工精度可以缩短磨合时间的磨合刹车次数。     

C/C复合材料飞机刹车盘的三维温度场

针对C/C复合材料飞机(B757)刹车盘制动过程中温度测量过程复杂和温度场难于表征的问题,采用有限元方法结合惯性台实验对其温度场进行了分析研究。根据刹车盘制动原理和传热原理,确定了温度场有限元分析中的载荷、边界条件和加载过程。通过仿真后处理形象地描述了制动过程中刹车盘温度场的变化,直观地表现了温度场分布状态。结果表明;在正常着陆的能量条件下中间静盘处测温点在46s时达到最高温度659℃;承压盘和压紧盘的测温点则在48.5s时达到最高温度,整个过程各点温度先升高后降低,中间静盘的热负荷最大,温升最快,承压盘次之,压紧盘最小。对比实验测量与仿真结果,两者吻合较好,证实温度场的有效性。     

密度对C/C复合材料热力学性能的影响

采用针刺预制体经化学气相沉积与沥青浸渍-高压碳化致密工艺制备C/C复合材料,通过控制沥青浸渍-高压碳化致密次数,获得了密度分别为1.70g/cm~3、1.82g/cm~3、1.89g/cm~3的三种C/C材料,测试材料的力学、热学性能。结果表明材料拉伸强度随密度升高而降低。当密度较低时,纤维/基体界面结合强度相对较低,可以延缓纤维断裂的发生;拉伸断口显示出假塑性断裂特征,有利于材料拉伸强度的提高。材料的压缩强度与剪切性能密切相关,且均随密度升高表现出先升后降的趋势。材料的热膨胀系数随密度升高而增大,材料中微晶之间的空隙在受热过程中可以吸收一部分膨胀量,因此对于C/C材料,降低密度有利于降低热膨胀系数。材料导热系数随密度升高而明显增大,且随密度升高,微晶尺寸增大,有利于晶格振动的传递,从而使得导热系数增大。热应力因子随密度升高而先升后降,作为热结构件使用时,采用密度为1.82g/cm~3的C/C材料可以获得相对较高的抗热震能力。在C/C材料研究开发中,可以综合对材料力学、热学性能的要求来对C/C材料密度指标进行设计。     

国外C/C复合材料飞机刹车盘的摩擦表面特性和摩擦磨损机理

在MM-1000型摩擦试验机上,对英、法、美三国四大炭盘制造商的五种炭盘小样进行了摩擦磨损性能测试,对摩擦表面进行了宏观和扫描电子显微镜(SEM)微观形貌分析,对各试样的摩擦磨损过程和机理进行了一定的探讨.结果表明:石墨化度决定了膜的完整程度,且成正比关系,坯体结构对摩擦膜有一定的影响;纯树脂炭基体的试样表面膜厚度较小,完整致密性与热解炭基体的试样差别较大,磨损较大;C/C复合材料的机械磨损以粘着、犁沟、磨粒磨损为主,膜越完整的材料呈现出以粘着磨损为主,对于低石墨化度的和纯树脂炭基体的C/C复合材料表现出犁沟、磨粒磨损为主,粘着磨损为辅.     

不同C/C复合材料飞机刹车盘基本性能的对比分析

通过对比分析Dunlop、 B.F.Goodrich、Missier、Bendix和中南大学粉末冶金研究所制备的几种炭/炭复合材料的显微组织、石墨化度、导热系数、洛氏硬度、抗压、抗弯、层间剪切强度、摩擦磨损性能后,得出如下结论:C/C复合材料作为一种性能优良的制动材料,必须具有合理的炭纤维骨架结构,一定比例的粗糙层气相沉积炭结构,较高的石墨化度和垂直摩擦面方向上的导热系数;我国具有自己知识产权的C/C复合材料飞机刹车盘的研制工作已取得了较大的进展和突破,其各项性能指标与国外同类产品性能相当。     

飞机炭刹车盘粘接修复技术研究

探讨了适用于Ｃ／Ｃ复合材料粘接的新方法、新工艺,对Ｃ／Ｃ复合材料粘接试样进行了常温性能、抗热冲击性能的测试,采用ＳＥＭ对粘接界面和破坏断面进行了观察和分析。同时,进行了粘接法修复的Ｂ７５７－２００飞机炭盘地面动力模拟试验。说明了 妆修复是一种有效的修复方法。     

飞机炭刹车盘的快速气相沉炭

研制了热梯度定向气流法制备炭／炭复合材料飞机刹车盘的设备,通过对气相沉炭工艺的优化,可以达到快速气相沉炭的目的,设备的能源消耗低,原料气的有效利用率高,材料的热导率高,摩擦性能好,肋的生产成本低。     

C/C刹车盘的结构及断口分析

用腐蚀方法解剖了几种C／C复合材料刹车盘,分析了它们预成型体的结构,用扫描电子显微镜观察了C／C复合材料的刹车盘的平行盘面及垂直盘面的断口,分析了炭纤维与基体之间的界面特征。     

飞机炭刹车盘抗氧化性能的研究

采用Ｓｉ－Ｂ系组分表面涂层对收音机炭刹车盘进行抗氧化处理，涂层中的Ｂ组分在高温下形成的玻璃态Ｂ２Ｏ３能有效地愈合涂层及炭材料本身的缺陷，抑制其氧化活性点，得到的涂层可以满足飞机炭刹车盘抗氧化处理的要求。     

C/C复合材料摩擦磨损性能研究

综述了国内外对C/C复合材料摩擦磨损性能的研究现状.指出C/C复合材料的摩擦磨损机理为机械磨损和氧化磨损,在高温下(500℃以上)C/C复合材料的磨损是机械磨损和氧化磨损共同作用的结果,而氧化是磨损的根本原因;影响C/C复合材料摩擦磨损性能的因素有材料本身的因素,如复合材料的热解炭结构、密度、石墨化度、防氧化涂层等,也有实际操作条件的因素如刹车环境、刹车过程中的刹车速度、刹车能量等.提出对不同工艺制备的C/C复合材料的摩擦磨损性能有待于进一步研究.     

飞机刹车用长寿命高摩擦特性炭/炭复合材料制备技术(英文)

以针刺炭纤维准三向结构整体毡为预制体,经丙烯气体狭缝定向流的"外热内冷"、"内热外冷"径向热梯度CVI工艺致密技术,优化组合的热解炭/树脂炭双元炭基体技术,通过调控高温处理技术等三大关键技术制备了A320系列飞机炭刹车盘材料。与现用的A320系列飞机进口炭刹车盘进行了地面台架对比试验和装机应用。结果表明:自主开发的炭刹车盘其设计着陆能量和超载着陆能量的摩擦特性与国外相当,但在高能载(RTO)刹车时,其摩擦系数提高了21%～48%,静摩擦系数提高了28%;装机应用寿命平均达到2700次以上,比国外产品寿命提高了23%,凸现出长使用寿命和高摩擦特性的特色。     

C/C刹车盘快速致密化工艺及其性能

为了缩短C/C刹车盘制备周期并提高其性能,介绍了一种制备C/C飞机刹车盘的快速致密化工艺,即采用天然气与丙烷气的混合气体为炭源气体的等温压差CVI法。与常规致密化工艺（丙烯气为炭源气体的等温压差CVI法）相比,C/C刹车盘的CVI(Chemical vapor infiltration) 时间缩短了一半,其导热性能提高5%以上,拉伸、压缩、弯曲与剪切性能提高10%以上,摩擦磨损性能提高20%以上。      

Effect of braking pressure and braking speed on the tribological properties of C/SiC aircraft brake materials

Effects of braking pressure and braking speed on the tribological properties of C/SiC aircraft brake materials has been studied using a disk-on-disk type laboratory scale dynamometer. The braking temperature increased with increasing braking speed and was less affected by changes in braking pressure. The friction coefficient increased to the maximum value at 10 m/s and then fell with the increase of braking speed at the same braking pressure. The friction coefficient decreased with the increase of braking pressure at the same braking speed. The wear rate increased with braking speed increasing at the same braking pressure. The wear rate was little at braking speed below 20 m/s, and rapidly increased when the braking speed exceeded 20 m/s.     

Effect of isotropic interlayers on the mechanical and thermal properties of carbon/carbon composites

Multilayer which consists of isotropic (ISO) interlayer and rough laminar (RL) and single RL structure carbon/carbon (C/C) composites have been prepared by isothermal chemical vapor infiltration at 5 and 1 kPa. Mechanical and thermal properties of both composites have also been studied. Experimental results indicate that ISO interlayer between fiber and matrix plays an important role on fracture behavior and strength of the composites. Comparing with single RL structure composites, the strength decrease of composites with ISO interlayers is about 28-40%. ISO interlayer is the main source of fracture due to its low density and micropores between crystallites. The low thermal conductivity of ISO interlayers also results in the thermal property degradation of obtained C/C composites. By reducing infiltration pressure, the ISO interlayers are substituted by compact RL matrix which improves the general properties of C/C composites.     

等离子处理碳纤维织物复合材料的摩擦学性能

将碳纤维织物浸渍-涂层酚醛-缩醛粘结剂树脂,加压固化后制备出碳纤维织物复合材料.分析了摩擦磨损表面和经等离子体处理后碳纤维织物化学组成的变化,研究了摩擦磨损性能、拉伸性能和粘结性能.结果表明,碳纤维织物的磨损分为严重磨损和稳定磨损两个阶段,其中严重磨损阶段的磨损量占了总磨损量的87%.经过等离子体处理后,在碳纤维织物的表面产生了许多活性基团如羰基、羧基、酯基,表面活性元素的含量明显增多;碳纤维织物的浸润性增大,提高了其与粘结剂的结合强度和结合量,增强了织物纤维束间的结合力;固化后与粘结剂构成很好的整体材料,增强了纤维束抗变形和抗断裂能力,使载荷和摩擦力可以平均的分配在纤维上,避免应力集中,从而提高了碳纤维织物复合材料的摩擦学性能和力学性能.     

Friction and wear behavior of carbon fiber reinforced brake materials

A new composite brake material was fabricated with metallic powders, barium sulphate and modified phenolic resin as the matrix and carbon fiber as the reinforced material. The friction, wear and fade characteristics of this composite were determined using a D-MS friction material testing machine. The surface structure of carbon fiber reinforced friction materials was analyzed by scanning electronic microscopy (SEM). Glass fiberreinforced and asbestos fiber-reinforced composites with the same matrix were also fabricated for comparison. The carbon fiber-reinforced friction materials (CFRFM) shows lower wear rate than those of glass fiber- and asbestos fiber-reinforced composites in the temperature range of 100°C-300°C. It is interesting that the frictional coefficient of the carbon fiber-reinforced friction materials increases as frictional temperature increases from 100°C to 300°C, while the frictional coefficients of the other two composites decrease during the increasing temperatures. Based on the SEM observation, the wear mechanism of CFRFM at low temperatures included fiber thinning and pull-out. At high temperature, the phenolic matrix was degraded and more pull-out enhanced fiber was demonstrated. The properties of carbon fiber may be the main reason that the CFRFM possess excellent tribological performances.     

改性酚醛树脂陶瓷摩擦材料的摩擦磨损性能

以普通酚醛树脂、硼改性酚醛树脂、三聚氰胺改性酚醛树脂为黏结剂,以陶瓷纤维为增强纤维,制备了3种酚醛树脂陶瓷摩擦材料。对其冲击韧性和硬度进行实验测试,采用摩擦磨损试验机考察其摩擦磨损性能,采用扫描电子显微镜(SEM)和X射线能谱仪分析其磨损表面形貌及其成分,并探讨其磨损机制。结果表明:硼改性酚醛树脂黏结剂能够提高摩擦材料的硬度,三聚氰胺改性酚醛树脂黏结剂能够提高摩擦材料的冲击韧性,降低摩擦材料硬度;在摩擦过程中三聚氰胺改性酚醛树脂在高温下炭化,在摩擦材料表面形成一层致密的摩擦层,摩擦层的存在使摩擦材料的摩擦因数相对比较稳定,降低了摩擦材料的磨损率。     

Elevated temperature low cycle fatigue of grey cast iron used for automotive brake discs

This paper evaluates the fatigue life properties of low carbon grey cast iron (EN-GJL-250), which is widely used for automotive brake discs. Although several authors have examined mechanical and fatigue properties at room temperatures, there has been a lack of such data regarding brake discs operating temperatures. The tension, compression and low cycle fatigue properties were examined at room temperature (RT) and at brake discs’ working temperatures: 500 °C, 600 °C and 700 °C. The microstructure of the material was documented and analysed. Tensile stress–strain curves, cyclic hardening/softening curves, stress–strain hysteresis loops, and fatigue life curves were obtained for all the above-mentioned temperatures. It was concluded, that Young’s modulus is comparable with both tension and compression, but yield its strength and ultimate strength are approximately twice as great in compression than in tension. All the mechanical properties remained quite stable until 500 °C, where at 700 °C all deteriorated drastically. During fatigue testing, the samples endured at 500 °C on average at around 50% of cycles at room temperature. Similar to other materials’ properties, the cycles to failure have dropped significantly at 700 °C.     

In-plane shear strength of a carbon/carbon composite at different loading rates and temperatures

The in-plane shear strength (IPSS) of a carbon/carbon composite (C/C) was measured at different loading rates and temperatures by compressing the double-notched specimen (DNS). The fracture surfaces were examined by scanning electron microscopy. The results indicate that IPSS measured by loading in compressing DNS is very close to that determined by the Iosipescu method at room temperature. There is a linear relationship between IPSS and the loading rate on the log-log coordinate, as the loading rate increases from 0.005 to 2 mm/min. IPSS at 1873 K is about two times of that at room temperature. The results were caused by the degassing effect of the absorbed water, release of the thermal stress and enhancement of the fiber strength.     

碳纳米管/碳纤维/环氧树脂复合材料研究

制备了碳纳米管(CNTs)/碳纤维(CF)/环氧树脂(EP)三元复合材料。研究了CNTs含量对复合材料层间剪切强度、弯曲强度和弯曲模量的影响,并采用场发射扫描电镜分析了CNTs在基体树脂中的分散情况。结果表明:复合材料性能的变化源自于CNTs在基体树脂中的分散状态。当CNTs含量为0.2%(wt,下同)时,复合材料剪切强度和弯曲强度达到最大值,分别为99.2MPa和1811.4MPa,但其弯曲模量下降了8.7GPa。当CNTs添加量达到1%时,其弯曲模量达到135.9GPa,较未加入CNTs时提高了11.1%,层间剪切强度和弯曲强度分别降低了5.5MPa和359.5MPa。