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.

. Low Velocity Impact Fatigue Studies on Glass Epoxy Composite Laminates with Varied Material and Test Parameters - Effect of Incident Energy and Fibre Volume Fraction

Abstract: An effort made to study the effects of fiber volume fraction and incident13; energy on the impact damage tolerance of composite laminates subjected to low13; velocity impacts at constant strike velocities. Repeated drop tests were conducted using an13; inhouse built drop weight impact-tester: Delamination-area was used as parameter for13; quantifying damage while the number of drops (impacts) to failure use to assess the13; damage tolerance limits. The delamination area was found to increase and then saturate13; after a certain number of drops. Impact fatigue studies showed the existence of a critical13; Incident energy (Ec) around which design of opmposite structures can be based. Also the13; minimum incident energy required to fracture the sample in a single impact (ESDT)was13; evaluated from the data. One of the interesting observations made was that for any given13; incident energy, the delamination area was found to be minimum at a certain fiber volume13; fraction (0.5 in this case) of the laminate. This was explained on lines of failure13; mechanisms reported earlier.13;

Optimization of Helicopter Rotor Using Polynomial and Neural Network Metamodels

Abstract: This study aims to determine optimal locations of dual trailing-edge flaps and blade stiffness to achieve minimum hub vibration levels in a helicopter, with low penalty in terms of required trailing-edge flap control power. An aeroelastic analysis based on finite elements in space and time is used in conjunction with an optimal control algorithmtodeterminethe flaptimehistoryforvibrationminimization.Usingtheaeroelasticanalysis,itisfoundthat the objective functions are highly nonlinear and polynomial response surface approximations cannot describe the objectives adequately. A neural network is then used for approximating the objective functions for optimization. Pareto-optimal points minimizing both helicopter vibration and flap power are obtained using the response surface and neural network metamodels. The two metamodels give useful improved designs resulting in about 27% reduction in hub vibration and about 45% reduction in flap power. However, the design obtained using response surface is less sensitive to small perturbations in the design variables.

Analysis of stress intensity factor of a crack approaching welding bead

Abstract: An analysis of the stress intensity factor is made for a crack approaching the welding line from the normal direction in an infinite plate.

Microstructure and mechanical properties of Al – 3Mg – 0.25 Sc alloy sheets produced by cryorolling

Abstract: Al-3Mg-0.25Sc alloy with 50% and 75% rolling reductions from the initial thickness at room and cryogenic temperatures resulted in a higher dislocation density, enhanced lattice strain and reduced crystallite size for the cryorolled (CR) sample with 75% reduction (CR 75). A hierarchical grain size distribution was noted in CR samples through electron backscattered diffraction studies that led to a combination of 490 MPa of strength and 27% of ductility in CR 75. Also, due to hierarchical grain distribution, during the tensile test, deformation was expected to follow a complex strain distribution rather than localised necking, which had resulted in higher elongation. Further, a low mechanical anisotropy and a proportional decrement in texture index with a higher fraction of Cube texture enhanced the ductility of CR 75 among the rolled samples. Higher work hardening rate was reported by the CR samples than that of room temperature rolled (RTR) ones due to the influence of cryorolling and the existence of Al3Sc precipitates. Among the rolled samples, the CR 75 sample reported a higher necking percentage of 24% based on the stress based necking limit and fracture limit diagram, which indicated its ability to withstand higher strain before failure was consistent with the mechanical properties reported.

Chromate and HF free pretreatment for MAO/electroless nickel coating on AZ31B magnesium alloy

Abstract: Micro arc oxidation (MAO) coating was developed as an interlayer for the electroless nickel (EN) top coat to improve the corrosion resistance of Mg alloy. Prior to the electroless nickel deposition, oxide layer was activated by using NaBH4 solution as a replacement for conventional chromate and HF activation processes. EN coatings were prepared using the alkaline carbonate bath. As-prepared coatings were characterized for the surface morphology and composition using Field Emission Scanning Electron Microscopy (FESEM) attached with energy dispersive analysis of X-ray (EDX). Potentiodynamic polarization studies were carried out in non-deaerated 3.5% NaCI solution to find out the corrosion resistance of the coatings. The MAO coating showed porous morphology with micro cracks whereas, MAO/Ni-P coating exhibited dense nodular structure. The cross-Ni-P and MAO/Ni-P/Ni-W-P duplex al images showed good adhesion between MAO and Ni-P layers. This clearly indicates that the present activation process results in dense with uniform pores of MAO coating along with excellent bonding at the interface for Ni-P coat. The MAO/EN coating combination showed two orders improvements in corrosion resistance as compared with the substrate. (C) 2017 Published by Elsevier B.V.