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首页> 外文学位 >Effect of relative humidity and kinetic energy on frictional performance of carbon-carbon composite materials (disc-on-disc configuration).
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Effect of relative humidity and kinetic energy on frictional performance of carbon-carbon composite materials (disc-on-disc configuration).

机译：相对湿度和动能对碳-碳复合材料摩擦性能的影响（盘对盘结构）。

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摘要

Carbon/carbon composites are used as frictional components in braking systems because of their unique properties, high melting temperature, excellent thermal conductivity, high thermal capacity, low density and their ability to be used as both frictional and structural materials. However, the sensitivity of carbon/carbon brake materials to the environment, which has been attributed to moisture adsorbtion/desorption on the brake's surface, is known to be a significant factor influencing frictional performance [1]. In particular, the decrease in braking capacity ("morning sickness") and transition phenomenon (sudden increase in friction) has been attributed to moisture adsorption/desorption process [1]. In this work, the impact of kinetic energy dissipated during friction process and the impact of different environmental conditions on the frictional performance of selected carbon/carbon composite materials was studied.; The average coefficient of friction at landing energies of 2/D, carbon-carbon composite, composed of randomly chopped pitch fibers with smooth laminar CVI and charred resin matrix material (HWCCA) was found to be very sensitive to the energy level applied during braking, but it is less sensitive to humidity. At all humidity levels, the average CoF drastically decreased when the amount of kinetic energy dissipated in friction process increased. The average coefficient of friction at landing energies of 3/D, carbon-carbon composite composed of non-woven needled felt PAN fiber with a rough laminar CVI matrix material (HWCCD) was found to have modest sensitivity to the landing energy and humidity level. Slightly lower values of average CoF were detected at lower energies and higher humidity levels. Values of the average CoF were significantly influenced by the development of the transition phenomenon.; For HWCCA material, transients developed at all energy levels. At the 100% normal energy level, two transients were detected. Increases in energy level shorten the time for onset of the transient. At 50% NLE, the CoF is high from the beginning of the stop. Increase of the humidity level in the environment decreased oscillations of the friction coefficient and noise at all energy levels. For HWCCD material, the coefficient of friction was relatively stable at lower energy conditions (12.5 and 25% NLE). Drastic changes in the coefficient of friction occurred the when energy dissipated during the stop reached the 50% NLE. Two transients were observed when the energy dissipated during the stop increased to the level of 100% NLE. The kinetic energy dissipated during landing stops had no significant influence on the oscillation and noise level. Relative humidity level did not have a significant influence on the landing stops as far as oscillation and noise are concerned.; The time dependence of the CoF was shown to be closely correlated with the increase of temperature on the friction surfaces, in particular the occurrence of the transients. It was shown that the beginning and the end of the first transients occurred at the similar friction surface temperatures for both investigated materials. It was shown that oxygen (in dry air) slightly postponed the development of the transient, while the water vapor had significant influence. Water vapor also caused a decrease in the CoF at the very end of the stop, while no drop in the CoF was detected when tests were performed in dry nitrogen and dry air. It is therefore, reasonable to conclude that re-adsorption of water vapor on the friction surface is responsible for such behavior.; Comparison of the friction surface microstructures at two different transients of the CoF, of very similar values showed the microstructure of the friction surface was turbostratic at the first and highly ordered at the second transient. Therefore, no direct relationship between microstructure of the friction surface itself and frictional performance for investigated materials and simulated conditions c
机译：碳/碳复合材料因其独特的性能，高熔化温度，出色的导热性，高热容量，低密度以及可用作摩擦材料和结构材料的能力而被用作制动系统中的摩擦部件。然而，已知碳/碳制刹车材料对环境的敏感性（归因于制动器表面上的水分吸附/解吸）是影响摩擦性能的重要因素[1]。尤其是，制动能力的下降（“晨吐”）和过渡现象（摩擦突然增加）已归因于水分吸附/解吸过程[1]。在这项工作中，研究了摩擦过程中耗散的动能以及不同环境条件对所选碳/碳复合材料摩擦性能的影响。研究发现，由碳纤维/碳纤维复合材料组成的2 / D着陆能量的平均摩擦系数由具有光滑层状CVI的短切沥青纤维和炭化树脂基质材料（HWCCA）组成，对制动过程中施加的能级非常敏感，但是它对湿度不太敏感。在所有湿度水平下，当摩擦过程中消耗的动能增加时，平均CoF急剧下降。发现由无纺针刺毡PAN纤维和粗糙的层状CVI基质材料（HWCCD）组成的3 / D碳-碳复合材料在着陆能量上的平均摩擦系数对着陆能量和湿度水平具有中等敏感性。在较低的能量和较高的湿度下，检测到的平均CoF值略低。平均CoF值受过渡现象发展的显着影响。对于HWCCA材料，在所有能级上都会产生瞬变。在正常能量水平为100％时，检测到两个瞬变。能量水平的提高缩短了瞬变发生的时间。在NLE为50％时，CoF从停止位置开始就很高。环境中湿度水平的增加降低了所有能量水平下的摩擦系数和噪声的振荡。对于HWCCD材料，在较低的能量条件下（NLE为12.5和25％），摩擦系数相对稳定。当停止过程中耗散的能量达到NLE的50％时，发生了摩擦系数的急剧变化。当停止期间耗散的能量增加到100％NLE的水平时，观察到两个瞬变。着陆停止过程中耗散的动能对振动和噪声水平没有显着影响。就振动和噪声而言，相对湿度对降落站没有重大影响。结果表明，CoF的时间依赖性与摩擦表面温度的升高（特别是瞬变的发生）密切相关。结果表明，两种材料的第一次瞬变的开始和结束都发生在相似的摩擦表面温度下。结果表明，氧气（在干燥的空气中）略微延迟了瞬态的发展，而水蒸气具有显着影响。在停止的最后，水蒸气还会导致CoF降低，而在干燥氮气和干燥空气中进行测试时，CoF却没有下降。因此，可以合理地得出结论，水蒸气在摩擦表面上的重新吸附是造成这种行为的原因。比较CoF的两个不同瞬态下的摩擦表面微观结构，其值非常相似，表明摩擦表面的微观结构在第一个瞬态处是涡轮层，在第二个瞬态处是高度有序的。因此，对于所研究的材料和模拟条件，摩擦表面本身的微观结构与摩擦性能之间没有直接关系。

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  • 作者

    Krkoska, Milan.;

  • 作者单位

    Southern Illinois University at Carbondale.$bMechanical Engineering.;

  • 授予单位 Southern Illinois University at Carbondale.$bMechanical Engineering.;
  • 学科 Engineering Mechanical.
  • 学位 M.S.
  • 年度 2007
  • 页码 139 p.
  • 总页数 139
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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