• Kalyani Vijayan

      Articles written in Bulletin of Materials Science

    • X-ray analysis of polycrystalline aluminium subjected to fatigue cycling

      Kalyani Vijayan A Mani C Balasingh A K Singh

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      Variations in the halfwidth values of X-ray reflections from fatigue-cycled, polycrystalline aluminium samples have been analysed. An oscillatory variation of the halfwidths with fatigue cycling has been observed. Analysis of the diffraction line profiles indicates that broadening arises mainly because of the build-up of microstrains during fatigue cycling. The present data indicate that (i) broadening due to fatigue cycling increases with glancing angle; (ii) changes in halfwidth and integral widths, due to fatigue cycling, are comparable and (iii) (b/b0) versusN curves for fatigue cycling under constant stress amplitude and flight loading conditions are comparable.

    • Crystallographic data on axially compressed Kevlar 49 fibres

      R V Iyer Kalyani Vijayan K Sooryanarayana T N Guru Row

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      Axially compressed Kevlar 49 fibres have been examined by X-ray diffraction methods. The most prominent effect of axial compression is the anisotropic deformation of the unit cell. Whereas thec-axial length, which corresponds to the chain axis, undergoes contraction, the basal plane dimensions manifest enlargement. The deformations increase with the extent of axial compression. The half-widths and the azimuthal spread of reflections also exhibit changes. The compression induced structural changes provide qualitative support to the experimentally observed reduction in tensile strength and modulus.

    • Decomposition behaviour of Kevlar 49 fibres: Part I. AtTTd

      R V Iyer Kalyani Vijayan

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      The structural changes which accompany decomposition of Kevlar 49 fibres atT=500°C and 550°C, respectively, have been elucidated. At both these temperatures, cumulative thermal exposures of specific durations,tcum(T), are required to result in decomposition. The conspicuous features which characterize isothermal decomposition of the fibres are: (i) progressive reduction and an eventual total loss in fibre crystallinity, (ii) progressive loss in weight, (iii) introduction of surface damages, (iv) introduction of hollowness, and (v) deterioration in tensile properties.

    • Effect of penetrants on the aramid Nomex

      Anjana Jain Kalyani Vijayan

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      The response of Nomex sheets to some penetrants has been analyzed. The process of moisture uptake depends on the relative humidity (RH) of the ambient atmosphere and the initial characteristics of the polymer. In the case of common laboratory solvents,the uptake by the polymer shows an inverse dependence on the molar volume of the former. Although the calendered and the uncalendered Nomex sheets exhibit an overall similarity in their response to various penetrants,quantitative comparison reveals distinct differences.

    • Thermally induced structural changes in Nomex fibres

      Anjana Jain Kalyani Vijayan

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      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.

    • Forbidden reflections from the aramid PPTA—A novel correlation with stacking faults

      Anjana Jain Kalyani Vijayan

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      The occurrence of space group forbidden reflections in the X-ray diffraction patterns from the aramid PPTA has been correlated with the presence of stacking faults. The fraction of sample affected by the presence of such faults has also been estimated.

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      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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