Effect of Environmental Exposures on the Aramid Fibre Kevlar

The effects of exposure of Kevlar 49 fibres to thermal, ultrasonic and chemical environments have been analysed. Both the tensile strength and the tensile modulus deteriorate with thermal exposures . However, the former is more sensitive than the latter. The prominent crystal structural changes induced by thermal exposures are reduction in crystallinity, molecular misalignment about the fibre axis, increase in the inter layer distance, changes in crystallite size and/or microstrain. Thermally induced macro changes include introduction of surface holes, partial hollowness near the core, localised thinning, material loss in the vicinity of surface impurities etc . The structural changes could be satisfactorily correlated with the corresponding changes in tensile properties . All the thermally induced effects are controlled by two parameters, viz ., the temperature (T) and the duration of the cumulative exposure to T, te,,,,,(T). The T-tcam(T) effect leads to the observation of isothermal decomposition of Kevlar over a range of temperatures which include T's, far below the reported decomposition temperature of 500/550 °C. A hitherto unknown direct correlation between X-ray diffraction peak positions and the tensile strength has also been identified . Exposure to ultrasonic waves introduces axial compression, evinced by the formation of kink bands, fibrillation and macro buckling . The unit cell of axially compressed fibres manifests an anisotropic deformation. The process of moisture uptake by Kevlar 49 fibres is controlled by the relative humidity (RH) of ambient atmosphere . The saturation moisture content is, however, determined by structural characteristics such as the degree of crystallinity, molecular alignment etc . The uptake of common organic solvents by Kevlar is dependent on the molar volume of the former

Women in Aerospace in India: Aerowoman

The main objective of the seminar was to bring together the Indian women in the field of aerospace and identify their scientific and technical contributions. In this context, the seminar was perhaps the first of its kind held in India. It was also aptly conducted in the x2018;Womenx2019;s Empowerment Year x2013; 2001x2019; declared by the Govt. of India.13

Effect of thermal aging on the crystal structural characteristics of poly(tetra fluoro ethylene)

The residual effects of cumulative thermal aging on the crystal structural characteristics of the fluoro carbon poly(tetra fluoro ethylene) (PTFE) have been studied by X-ray diffraction methods. The initial hexagonal arrangement of the PTFE chains in a 157 helical conformation is left unaffected by the exposures to temperatures (T), up to and beyond its melting point, Tm. The unit cell registers a residual anisotropic volume expansion. The anisotropy arises from the enhanced enlargement of the basal plane dimension a compared with the axial dimension c. Conformational changes contributing to the observed increase in the chain length have been examined. Enhancement of residual crystallinity of samples aged at T's lt; Tm suggests that the selective thermal aging could be used as an effective tool to improve the initial crystallinity of commercially available PTFE. The activation energy for 50% enhancement in initial crystallinity has been estimated as 53.9 kJ mol-1. Aging at 400xB0;C, a temperature above Tm, is accompanied by markedly different features viz., deterioration in crystallinity and other structural characteristics. The overall behavior of thermally aged PTFE bears a marked similarity to many polyamides. POLYM. ENG. SCI., 47:1724-1729, 2007. xA9; 2007 Society of Plastics Engineer

Thermally induced structural changes in Nomex fibres

Thermally aged Nomex fibres manifest several residual effects viz. reduction in X-ray crystallinity, weight loss and deterioration in tensile characteristics. Surface damages in the form of longitudinal openings, holes, material deposits etc have also been observed. Based on the data from thermally exposed fibres, the time needed for states of zero tensile strength and modulus have been predicted

Investigations on the Problem of Moisture Absorption13; by Kevlar Fibres

Kevlar fibres are know, to have affinity for moisture. We have investigated (i) the effect of relative humidity (RH) of ambient atmosphere and ( ii ) the effect of crystallinity of fibres on the process of moisture uptake.13; For RH values ranging fran 3 to 80% variation of moisture content of initially dry fibres with time has been measured. It is found that saturation moisture content varies with RH value. Specimens in which crystallinity has been reduced by apropriate treatmrent exhibit a marked increase in moisture content.Experiments on the effect of soaking the fibres in water at 26xB0;C and 98xB0;C have also been carried out. The site of ITOisture absorption has been studied using X-ray of dry Kevlar 49 fibres and those with clifferent levels13; of misture content. The results suggest that water molecules do not enter the unit cell

Conservation and management of marine fishery resources of Kerala State, India

The highly productive fisheries of Kerala, India, are suffering from overexploitation. Use of unsuitable fishing gears that result in a high level of wasteful bycatch and destruction of egg bearing and juvenile fish should be controlled. This paper makes some suggestions for monitoring and conservation of the fisheries in Kerala

Comment: Monitoring Networked Applications With Incremental Quantile Estimation

Our comments are in two parts. First, we make some observations regarding the methodology in Chambers et al. [arXiv:0708.0302]. Second, we briefly describe another interesting network monitoring problem that arises in the context of assessing quality of service, such as loss rates and delay distributions, in packet-switched networks.Comment: Published at http://dx.doi.org/10.1214/088342306000000600 in the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org