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.

Strength and stiffness optimization studies on honeycomb core sandwich panels

Abstract: The optimization of strength and stiffness properties of sandwich panels is a critical area of study in the effective design of sandwich panels in view of their potentialities in weight critical applications. G. R. Froud in his article aptly named 'Your sandwich order, Sir' (Froud, G. R. (1980). Your Sandwich Order, Sir, Composites, 133-138), shows theoretically how a sandwich construction can be optimally designed for a stiffness or a strength criterion. This article has triggered the interest and has prompted the authors, to carry out experimental studies, to verify the applicability of this theory to sandwich panel specimens made out of glass/epoxy skins with honeycomb core. The optimum core to skin weight ratios for maximum stiffness and strength of the sandwich panels are experimentally found to be 2.04 and 0.96 as against the theoretical values of 2.0 and 1.0.

Analysis of shear locking in Timoshenko beam elements using the function space approach

Abstract: Elements based purely on completeness and continuity requirements perform erroneously in a certain class of problems. These are called the locking situations, and a variety of phenomena like shear locking, membrane locking, volumetric locking, etc., have been identified. Locking has been eliminated by many techniques, e.g. reduced integration, addition of bubble functions, use of assumed strain approaches, mixed and hybrid approaches, etc. In this paper, we review the field consistency paradigm using a function space model, and propose a method to identify field-inconsistent spaces for projections that show locking behaviour. The case of the Timoshenko beam serves as an illustrative example.

Influence of scandium on an Al–2% Si alloy processed by high-pressure torsion

Abstract: High-pressure torsion (HPT) was used to process Al–2% Si and Al–2% Si–0.25% Sc alloys for up to five turns and the mechanical properties of the processed materials were evaluated using the ball indentation technique (BIT). The results show that the presence of Al3Sc precipitates is effective in producing higher strength levels and greater grain refinement in the Al–2% Si–0.25% Sc alloy. The introduction of scandium reduces the grain size of the Al–2% Si alloy from ∼0.38 to ∼0.15 μm after 5 turns of HPT and the corresponding maximum tensile strength is increased from ∼325 to ∼375 MPa. The grain and substructure formation in the Al–2% Si alloy is similar to aluminum with dislocation cell formation and a reasonably recovered microstructure whereas in the Al–2% Si–0.25% Sc alloy it is non-homogeneous with arrays of non-equilibrium boundaries and dislocation tangles within the grains.

Turbulent drag reduction using riblets on a supercritical airfoil at transonic speeds

Abstract: Numerous studies have shown that viscous drag reduction of 4-8% at low speeds can be achieved in simple two-dimensional flows at wind-tunnel Reynolds numbers. Because of the encouraging benefits realized at low speeds, an evaluation of riblet effectiveness at subsonic and transonic speeds, both in wind tunnels and flight, has been reported. Realistic applications involve, among other factors, pressure gradient (eg, airfoil and wing) and three-dimensionality. Drag reductions under these conditions are being assessed currently. This paper presents recent results of drag reduction using 3M riblets on a supercritical airfoil at transonic speeds covering an angle of attack range of -0.5 to 1 deg, which is relevant to cruise conditions. (Authors)