Effect Of Fiber Type Research Articles

Effect of fiber-types on the braking performances of carbon/carbon composites

The braking performance of carbon/carbon composites prepared from carbonized oxidized polyacrylonitrile fiber (OPF) and from carbon fiber (CF) felts were investigated using a friction performance tester to simulate the normal landing and rejected take-off conditions of an aircraft. The microstructures, worn surfaces and hardness of the composites were characterized by Raman spectrometry, scanning electron microscope and nanoindentation. Results showed that the OPF-derived composites have stable friction coefficients, friction curves and acceptable wear loss at two braking levels, while the friction coefficients of the CF-derived composites present a relatively obvious performance degradation. An increase in braking energy not only reduces the friction coefficient of both composites, but also significantly increases their wear. Due to the higher hardness of CFs that makes them harder to deform and crush, their debris may experience rolling friction and abrade the friction film, resulting in a lower friction coefficient and a higher wear loss, especially under rejected take-off conditions. However, outstanding braking performance is obtained for the OPF-derived composites under both braking conditions, because the softer fibers in the matrix and the loose OPF debris are easier to crush and to form beneficial friction films.

섬유 종류가 도로포장용 콘크리트의 기초적 특성에 미치는 영향

Korea Institute of Construction Technology, Goyang 411-712, KoreaABSTRACT The objective of the paper is to experimentally investigate the effect of commercially avaliable fiber types such aspolypropylene (PP), nylon (NY), polyvinyl alcohol (PVA) and cellulose (CL) on the engineering properties of concrete for pavementapplication. The results, showed the fluidity tends to decrease with fibers addition compared to that of plain concrete. As for the effectof fiber types on fluidity loss, use of NY appear to give the most favorable results among all of the fiber types investigated in thisstudy while the effect of the fibers on air content was negligible. For the properties of hardened concrete, compressive and flexuralstrengths increased with fibers compared to plain concrete. The contribution of NY fibers to strength was the highest followed in theorder by NY, PVA, PP, and CL. However, in the case of the splitting tensile strength, its values were increased with NY and PP only.For porosity based on MIP(mercury intrusion penetration) method, the number of around 1 was observed when NY was mixed result-ing in increased cumulated amounts of porosity compared with that of plain mix. Thus, based on the consideration of fluidity andstrength it was found that the addition of NY fiber showed the optimal results under the conditions applied in this study.Keywords

Effects of fiber-types on braking behavior of carbon–carbon composites

The effects of fiber-types (PAN-T300 (CF), PAN-oxidized fiber (OF)) on the friction and wear behavior of C/C composites were investigated. The C/C composites were fabricated by densifying porous needle-punched felts with isothermal chemical vapor infiltration to 1.40 g/cm 3 followed by phenolic resin impregnation and carbonization till the ultimate density of about 1.75 g/cm 3. Carbon fiber/pyrocarbon interfacial strength was measured by single fiber push-out test. And the flexural strength compressive strength of the composites was tested. The braking behavior was investigated by modeling normal braking conditions of aircraft. The fiber/matrix interfacial strength of the OF-derived composite is higher and the flexural strength and compressive strength is lower than that of the CF-derived composite. The needle-punched felt made from OF, result in C/C composite with higher and much more stable friction coefficient, but higher mass wear, than the composites with the porous preform made from CF. Combining fracture of composite and carbon fiber/matrix interface, a modified friction mechanism is suggested that a suitable flexural strength of the composite and carbon fiber/matrix interfacial strength favors formation of friction films. The friction film can result in higher and more friction coefficient.