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.

Some aspects of high-speed blunt body flow computations with Roe scheme

Abstract: This paper discusses some aspects of three-dimensional supersonic and hypersonic inviscid blunt body flow computations. The method used is based on the solution of the Euler equations employing an explicit, upwind total variation diminishing formulation of the Roe Riemann solver within the cell-centered finite volume approach. A comparative study of various total variation diminishing limiters and entropy fixes is carried out to identify the most appropriate combination. The effect of using cell spacing in the total variation diminishing extrapolations is highlighted. Furthermore, a Mach number dependence and grid sensitivity study is carried out on various total variation diminishing limiters scaled with mesh spacing. Local time stepping and code parallelization has been employed to accelerate convergence in terms of effective wall clock times.

Effect of atmospheric pressure plasma treatment for repair of polymer matrix composite for aerospace applications

Abstract: This paper investigates the repair of polymer matrix composites and validates the repair by static testing. Scarf repair is carried out on the laminates and cured under vacuum. It is observed that ...

A two-step approach for synthesis, characterization and analysis of dicyclopentadiene–urea formaldehyde–siloxane-based double-walled microcapsules used in self-healing composites

Abstract: Microencapsulation is a widely used method for making healing agents used in self-healing composites. In this study, a novel two-stage process was used to make double-walled microcapsules. Dicyclopentadiene–urea formaldehyde (DCPD–UF) microcapsules were synthesized by in situ polymerization of oil-in-water emulsion followed by siloxane coating through ‘sol–gel process’ (DCPD–UF–siloxane microcapsules). Average diameter of microcapsules, UF shell thickness and siloxane coating thickness were found to be 300, 1.4 and 16 µm, respectively. The effect of addition of microcapsules on rheological properties of epoxy was studied. Breaking pattern of single-walled and double-walled microcapsules immersed in epoxy was analyzed by continuous monitoring of the deformation behavior through a rheometer–microscope arrangement, confirming improved mechanical properties of the double-walled microcapsules. In this study, epoxy resin cast specimens with and without microcapsules were prepared and the effect of microcapsules on mechanical properties was examined. Epoxy specimens with double-walled microcapsules were found to be having improved mechanical properties compared to those with single-walled microcapsules. Finally, healing efficiency of DCPD–UF–siloxane microcapsules in epoxy was observed to be marginally higher, and therefore, this double-walled microcapsule system is shown to be a promising candidate for further self-healing composite investigations.

Mechanical behavior and void coalescence analysis of cryorolled AA8090 alloy

Abstract: Aluminum lithium alloy was rolled at two different temperatures, viz., 28 °C (301 K) and −196 °C (77 K). The thickness of the alloy was reduced by 75 % from its initial thickness (6 mm) in each condition. X-ray diffraction analysis was carried out on all samples to determine the grain size and dislocation density. The cryorolled sample exhibited a finer grain size with higher dislocation density, which was evidenced from micrographs obtained with transmission electron microscopy. Electron backscattered diffraction images revealed the presence of bimodal grain distribution in the rolled samples, in which the cryorolled sample exhibited a larger amount of ultrafine grains. Both tensile and hardness tests were performed on rolled samples. Cryorolled samples showed superior properties when comparing with room temperature rolled sample. Scanning electron microscopic images of fractured samples were used to analyze the void coalescence behavior. The various void coalescence parameters like void size, void area, length to width ratio of void, and ligament thickness were analyzed, and these results were correlated with microstructure, mechanical properties, crystallite size, and dislocation density in all conditions.