Defence Research and Development Laboratory

About: Defence Research and Development Laboratory is a facility organization based out in Hyderabad, India. It is known for research contribution in the topics: Mach number & Turbulence. The organization has 404 authors who have published 420 publications receiving 4183 citations. The organization is also known as: DRDL.

Epoxy benzoxazine based ternary systems of improved thermo-mechanical behavior for structural composite applications

Abstract: Ternary mixtures of various ratios of bisphenol F benzoxazine as a hardener for bisphenol F novolac epoxy (ER) and diglycidal ether of polyethylene glycol (EL) resins were made in order to study the visco elastic and thermo mechanical properties in comparison with homo polymerized polybenzoxazine (F-a). FTIR, and DSC were used to characterize the cure characteristic. The dynamic mechanical analyzer and thermo gravimetric analysis were investigated on F-a and ternary samples. An improved Tg of curable ternary mixture with 48.1 and 3.1 wt% of ER and EL respectively with benzoxazine resin was achieved based on trends in the ternary diagram. The ternary samples were thermally stable up to 370 °C when compared to F-a. Investigation of fracture toughness and SEM images showed improved fracture toughness for the samples with 52% binary epoxy mixture in the ternary system. The newly developed ternary mixtures showed improved service temperature, thermal stability, cross linking density, processing window and fracture toughness with minimum brittleness when compared to polybenzoxazine. The applicability of the developed ternary mixture was demonstrated by preparing an S glass fabric reinforced composite with F-f. It was observed that this S glass fabric composite has improved flexural strength, flexural modulus, ILSS, Shore D hardness & hydrolytic stability when compared to the polybenzoxazine composite and was found to be very useful for high performance structural applications.

Dissimilar Joining of Stainless Steel and 5083 Aluminum Alloy Sheets by Gas Tungsten Arc Welding-Brazing Process

Abstract: The dissimilar joining using gas tungsten arc welding - brazing of 304 stainless steel to 5083 Al alloy had been conducted with the addition of Al-Cu eutectic filler metal. The interface microstructure formation between filler metal and substrates, and spreading of the filler metal were studied. The interface microstructure between filler metal and aluminum alloy characterized that the formation of pores and elongated grains with the initiation of micro cracks. The spreading of the liquid braze filler on stainless steel side packed the edges and appeared as convex shape, whereas a concave shape has been formed on aluminum side. The major compounds formed at the fusion zone interface were determined by using X-ray diffraction techniques and energy-dispersive X-ray spectroscopy analysis. The micro hardness at the weld interfaces found to be higher than the substrates owing to the presence of Fe2Al5 and CuAl2 intermetallic compounds. The maximum tensile strength of the weld joints was about 95 MPa, and the tensile fracture occurred at heat affected zone on weak material of the aluminum side and/or at stainless steel/weld seam interface along intermetallic layer. The interface formation and its effect on mechanical properties of the welds during gas tungsten arc welding-brazing has been discussed.