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.

Stationary crack tip fields in elastic–plastic solids: an overview of recent numerical simulations

Abstract: In this paper, an overview of some recent numerical simulations of stationary crack tip fields in elastic-plastic solids is presented. First, asymptotic analyses carried out within the framework of 2D plane strain or plane stress conditions in both pressure insensitive and pressure sensitive plastic solids are reviewed. This is followed by discussion of salient results obtained from recent computational studies. These pertain to 3D characteristics of elastic-plastic near-front fields under mixed mode loading, mechanics of fracture and simulation of near-tip shear banding process of amorphous alloys and influence of crack tip constraint on the structure of near-tip fields in ductile single crystals. These results serve to illustrate several important features associated with stress and strain distributions near the crack tip and provide the foundation for understanding the operative failure mechanisms. The paper concludes by highlighting some of the future prospects for this field of study.

A comparative study of the preparation and characterization of aromatic and aliphatic bismaleimides to produce modified siliconized epoxy intercrosslinked matrices for engineering applications

Abstract: A novel hybrid intercrosslinked network of hydroxyl-terminated polydimethylsiloxane modified epoxy and bismaleimides [N,N′-bismaleimido-4,4′-diphenylmethane and 1,6-bis(maleimido)hexane] matrix systems were developed. Epoxy resin was modified with 5, 10, and 15% (wt%) of hydroxyl-terminated polydimethylsiloxane using γ-aminopropyltriethoxysilane as crosslinking agent and dibutyltindilaurate as catalyst. The reaction between hydroxyl-terminated polydimethylsiloxane and epoxy resin was confirmed by IR spectral studies. The siliconized epoxy systems were further modified with 5, 10, and 15% (wt%) of both aromatic and aliphatic bismaleimides separately. The castings and E-glass fiber-reinforced composites prepared were characterized for their mechanical properties. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of the matrix samples were also performed to determine the glass transition temperature (T g) and thermal degradation temperature of the hybrid intercrosslinked systems. D...

In-Vitro Biocompatibility Studies of Plasma-Nitrided Titanium Alloy β-21S Using Fibroblast Cells

Abstract: In the present work, titanium alloy β-21S was nitrided in a low-pressure RF plasma with 100% nitrogen and 20% hydrogen-diluted nitrogen at 800 °C for 4 h and the samples were evaluated for in-vitro biocompatibility by using NIH 3T3 fibroblast cell line. Cellular behavior was evaluated in terms of cell morphology and its viability. FESEM was exploited to observe the morphology of the cells fixed over the surface of the implant. Fibroblasts were seemed to be well distributed over the surface with its characteristic spindle-like shape. Over all, the results indicate that nitriding provided a compatible surface for cell attachment and cell growth. Cell viability and proliferation was assessed by using standard MTT assay. Compared with substrate, the nitrided samples exhibited high-percentage cell viability demonstrating their increased biocompatibility. In addition, the nitrided samples facilitate bone-like apatite formation and exhibited a gradual increase of apatite formation after immersion in Hanks’ solution.

The key role of thread and needle selection towards ‘through-thickness reinforcement’ in tufted carbon fiber-epoxy laminates

Abstract: Tufting of dry preforms is one of the means of accomplishing through-thickness reinforcement (TTR) in a liquid composite molding process. Herein, once a preform is laid up, an automated robotic tufting setup is used to introduce the TTR. The selection of thread and needle for tufting process go hand-in-hand as tufting operation involves the act of penetrating preform by the needle as well as the trauma thread has to endure during this act. This paper explores the methodology of thread and needle selection through studies at different levels right from tufting of preforms to testing of tufted laminates. Glass, carbon and Kevlar threads in combination with a tufting needle and two different sewing needles are explored in this study. The effect of tufting speed on the quality of tuft is analyzed in terms of damage of fabric yarn, thread, and needle breakage. Layer-wise analysis of damage due to needle penetration in fabric yarns is carried out. Key mechanical properties of tufted composite samples are evaluated to determine the effect of tufting on the in-plane and out-of-plane properties.

Nose Blowing for Side Force Control on Slender Cones at High Incidence

Abstract: Vortex asymmetry on axisymmetric pointed forebodies at high angles of incidence results in side forces and adverse yawing moments even in symmetric flight. An experimental investigation has been carried out at low speeds to study the effectiveness of axial nose blowing against the oncoming flow for side force control on two slender cones. Tests were made on the 8 and 12 deg cone models with (circular)jet flow over a Reynolds number range of $0.4\times10^6$ to $5.4\times10^6$. Jet-to-freestream velocity ratio was varied up to 2.0, and the blowing diameter was varied as well. Force measurements were carried over the incidence range of 0 to 45 deg, and limited surface pressure distributions were obtained on the 12 deg cone model. The results explicitly show the effectiveness of nose blowing for side force control over a wide range of Reynolds numbers, and minimum side force was reached around a jet velocity ratio of 1.0. An important result is that the side force reduction correlates with jet velocity ratio in the range of parameters studied. Broad similarities in the trend of side force reduction with the nose blowing and the nose bluntness suggest that the interaction of axial jet with freestream flow results, possibly, in what we may call "fluid dynamic blunting".