National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Progressive damage analysis of adhesively bonded patch repaired carbon fibre–reinforced polymer specimen under compression involving cohesive zone model

Abstract: In this paper, the in-plane compression behaviour of open-hole carbon fibre composite specimens adhesively bonded with the external carbon fibre composite patches on the single- and double side are...

Synthesis, characterization, and thermo-mechanical properties of poly(acrylonitrile-co-2,3-dimethyl-1,3-butadiene-co-itaconic acid) as carbon fibre polymer precursors

Abstract: Novel carbon fibre polymer precursor (CFP), viz., poly(acrylonitrile-co-2,3-dimethyl-1,3-butadiene-co-itaconic acid) was synthesized using solution polymerization process. Structural identification, bonding network were established using infrared, and nuclear magnetic resonance spectroscopic techniques. Molecular characteristics, such as different kinds of average molecular weights were estimated applying solution viscometry and size exclusion chromatography. The char yield of the polymers were found to be 45% wt through thermal gravimetry. The thermomechanical behaviour of novel carbon fibre polymers were investigated employing several thermal techniques. Thermomechanical data confirm that newly synthesized copolymers exhibit higher coefficient of linear thermal expansion in the range 74–1716 °C−1, softening temperature at 51 °C in contrast to the conventionally used (37–810 °C−1). Differential scanning calorimetry results show a distinct bimodal curves with a wider thermal exotherm starting from 220 °C with two peaks at a temperature difference of 25 °C and an slower energy release rate 2.5–5.0 J g−1 s−1, thereby releasing the heat over a extended period of time than a sudden release of heat (14.75 J g−1 s−1) as sharp peak as observed in the conventional precursors. The above facts indicate that new polymers can be used as polymer precursor for high tensile carbon fibres.

Novel optically active lead-free relaxor ferroelectric (Ba0.6Bi0.2Li0.2)TiO3

Abstract: We discovered a near room temperature lead-free relaxor-ferroelectric (Ba0.6Bi0.2Li0.2)TiO3 (BBLT) having A-site compositional disordered ABO3 perovskite structure. Microstructure-property relations revealed that the chemical inhomogeneities and development of local polar nano regions (PNRs) are responsible for dielectric dispersion as a function of probe frequencies and temperatures. Rietveld analysis indicates mixed crystal structure with 80% tetragonal structure (space group P4mm) and 20% orthorhombic structure (space group Amm2) which is confirmed by the high resolution transmission electron diffraction pattern. Dielectric constant and tangent loss dispersion with and without illumination of light obey nonlinear Vogel-Fulture relation. It shows slim polarization-hysteresis (P-E) loops and excellent displacement coefficients (d33 ~ 233 pm/V) near room temperature, which gradually diminish near the maximum dielectric dispersion temperature (Tm). The underlying physics for light-sensitive dielectric dispersion was probed by X-ray photon spectroscopy (XPS) which strongly suggests that mixed valence of bismuth ions, especially Bi5+ ions, are responsible for most of the optically active centers. Ultraviolet photoemission measurements showed most of the Ti ions are in 4+ states and sit at the centers of the TiO6 octahedra, which along with asymmetric hybridization between O 2p and Bi 6s orbitals appears to be the main driving force for net polarization. This BBLT material may open a new path for environmental friendly lead-free relaxor-ferroelectric research.