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 Characterization of Glass, Carbon and Kevlar Composites Using Repeated Drop Tests

Abstract: Low-velocity ( 1.2-2.4 m/s) repeated drop weight impact tests were carried out on advanced composites (glass, carbon, kevlar in epoxy matrix - LY 556, HT 972) using an instrumented impact test machine (DYNATUP 8250). The incident energies ranged from 3.5 to 15 J (constant impactor mass 5.42 kg). Number of drops to failure (Nf) data were obtained for the above with simultaneous recording of the load-time and energy-time traces. The extent of impact damage for glass and kevlar composites was interpreted using final delamination area maps (tracings). Results for all the three composites showed that with an increase in drop numbers, the peak load (PL) steadily decreased while the total energy (Et) increased, until failure. Also, as the incident energy (Ein) was varied in arithmetic progression, the number of drops to failure (Nf) varied in harmonic progression. Finally it was concluded that repeated drop tests with final delamination area maps assist in understanding the impact damage tolerance of polymer composites

Dry sliding wear properties of a 7075-T6 aluminum alloy coated with Ni-P (h) in different pretreatment conditions.

Abstract: Dry sliding wear behavior of electroless nickel-phosphorus (EN) coating of thickness 35 lm deposited on a 7075-T6 aluminum alloy was studied. EN was deposited from a bath with sodium hypophosphite as a reducing agent. In as-deposited conditions, plating with 6-9 wt.% phosphorus has a mixture of amorphous and microcrystalline phase. Three pretreatments of Zn (zincate), Ni strike and absorbed hypophosphite layer were given to the substrate before EN coating to examine their wear performance. The surface morphology of the pretreatments was studied by a confocal laser scanning microscope. The performances of these pretreatments of EN were evaluated by dry sliding wear studies and followed by SEM studies. The results suggest that the wear behavior of EN mostly depends on the pretreatment conditions. Heat treatment at temperature of 400 C can enhance the wear resistance properties for all types of pretreatment conditioned samples and in addition that the average coefficient of friction of 400 C specimens (lav) had minimum value as compared to 200 C specimens. Ni strike provided better interlocking adhesion between EN and Al and this pretreatment noticeably improved the wear, frictional and hardness behavior of the EN coatings on 7075 Al substrate and further enhanced it by heat treatment of 400 C/h.