Fibre reinforced composites of multifunctional epoxy resins

Glass and carbon fibre reinforced epoxy composites were fabricated for N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) and its formulated systems with tri- and di-functional reactive epoxy diluents using 30% diaminodiphenyl sulphone (DDS) as a curing agent. The epoxy laminates were evaluated for their physical, chemical and mechanical properties [at room (26°C) and high (100°C) temperatures]. A marginal increase (<20%) in the mechanical properties of CFRP was found compared with GFRP laminates. Incorporation of epoxy diluents altered the mechanical properties of the composites significantly. The incorporation of triglycidyl-4-aminophenol diluent to TGDDM systems resulted in an improvement in mechanical properties of about 2–6%.     

Silver nanoparticle synthesis: novel route for laser triggering of polyelectrolyte capsules

We have demonstrated the synthesis of light-sensitive polyelectrolyte capsules (PECs) by utilizing a novel polyol reduction method and investigated its applicability as photosensitive drug delivery vehicle. The nanostructured capsules were prepared via layer by layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on silica particles followed by in-situ synthesis of silver nanoparticles (NPs). Capsules without silver NPs were permeable to low molecular weight (M(w), 479 g/mol) rhodamine but impermeable to higher molecular weight fluorescence labeled dextran (FITC-dextran). However, capsules synthesized with silver NPs showed porous morphology and were permeable to higher molecular weight (M(w) 70 kDa) FITC-dextran also. These capsules were loaded with FITC-dextran using thermal encapsulation method by exploiting temperature induced shrinking of the capsules. During heat treatment the porous morphology of the capsules transformed into smooth pore free structure which prevents the movement of dextran into bulk during the loading process. When these loaded capsules are exposed to laser pulses, the capsule wall ruptured, resulting in the release of the loaded drug/dye. The rupture of the capsules was dependent on particle size, laser pulse energy and exposure time. The release was linear with time when pulse energy of 400 μJ was used and burst release was observed when pulse energy increased to 600 μJ.     

Comparative studies on performance of plain,perforated, threaded,and threaded–perforated pin fin: A numerical approach

A heat sink is a thermal management system for electrical and electronic appliances whose performance is a function of fin geometry, arrangement, and flow field. Earlier research addressed the enhancement in the heat dissipation capacity of the sink with a change in the geometry of the fin. However, the change should increase the heat transfer rate per unit weight and per unit volume. One such attempt is made in the present work, which deals with numerical forced convection heat transfer simulation over a pin fin with three different surface modifications, namely, threads, equilateral triangular perforation, and threads with perforations. A numerical investigation is performed for 0.5773–2.5574 mm pitch of threads, 3–4.8 mm size of perforation, and 2–8 m/s velocities of air. To describe the flow pattern around the fin and its variation with surface modification, streamline profiles are drawn which reveals that the fluid–solid interaction is improved either with threaded or perforated surface and is maximum for threaded–perforated fin. The enhanced convection rates bring down the local fin temperature and the maximum fin temperature, where the drop is more for the threaded surface than that of the perforated surface because of turbulence. A 10° drop in maximum fin temperature is achieved by replacing a plain pin fin with a threaded–perforated pin fin, and the drop is 8° with threads alone and 6° only with perforations. The increased fineness of threads and size of perforation further bring down the maximum fin temperature.     

Shock wave-material interaction in ZrB2–SiC based ultra high temperature ceramics for hypersonic applications

We investigate the thermochemical stability of ZrB₂–SiC based multiphase ceramics to hypersonic aerothermodynamic conditions in free piston shock tube with an objective to understand quantitatively the role of thermal shock and pressure. The developed ceramics sustained impulsive thermomechanical shock, under reflected shock pressure of 6.5 MPa and reflected shock temperature of 4160 K in dissociated oxygen, without structural failure. The conjugate heat transfer analysis predicts the surface temperature of ZrB₂–SiC to reach a maximum of 693 and 865 K, for ZrB₂–SiC–Ti. The transient shock-material response is characterized by surface oxidation of the investigated ceramics, when exposed to high enthalpy gaseous environment, as a consequence of the interaction with ultrafast-heated (10⁶ K/s) gas for ~5 ms. Spectroscopic and structural characterization reveals that addition of Ti improves thermomechanical shock resistance, which is attributed to the assemblage of refractory phases. Taken together, ZrB₂–SiC–Ti based multiphase ceramics exhibit favorable shock-material response under impulse loading.     

Analysis of interaction between geometry and efficiency of impeller pump using rapid prototyping

Design aids available today might have helped the pump designers to bring about theoretically the most efficient pumps, but the production technology and quality control during manufacture has not kept pace with such achievements in realizing the goals of developing energy efficient pumps. Pump designers often face the problem of selecting and optimizing a number of independent geometrical parameters whilst aiming at the desired efficiency from the pump. The only option is to approximate the theoretical design with experimental findings iteratively until the end result is achieved. Tremendous development of advanced manufacturing technology and computer technology has made rapid prototyping and computational fluid dynamics (CFD) techniques the right alternative method of reaching the target. Centrifugal pump impeller geometry, which contributes maximum complexity in flow during pump design, has been analysed in this work based on the parameters derived through computer-aided design (CAD) and CFD analysis. Using selective laser sintering, technique the impeller designed by CAD and two standard impellers commercially available for the same duty requirement is manufactured and their performance is tested to know their hydraulic efficiency. Results obtained from this work are useful for standardising pump impeller design and for developing energy-efficient pumps.     

Effect of catalyst on the curing of tetrafunctional epoxy resin formulations

Cure kinetics of tetraglycidyl 4,4′-diaminodiphenyl methane resin formulations with diaminodiphenylsulfone as hardener and borontrifluoride-ethylamine adduct as accelerator has been studied by differential scanning calorimetry (DSC) technique both dynamically and isothermally. The DSC scans show multiple exotherm peaks, indicating the complex nature of reaction. The curing exotherms obtained have been analysed to derive the kinetic parameters associated with the curing process. The heat of reaction shows a decreasing trend with increasing catalyst concentration.     

Simultaneous measurement of aerodynamic and heat transfer data for large angle blunt cones in hypersonic shock tunnel

Aerodynamic forces and fore-body convective surface heat transfer rates over a 60° apex-angle blunt cone have been simultaneously measured at a nominal Mach number of 5.75 in the hypersonic shock tunnel HST2. An aluminum model incorporating a three-component accelerometer-based balance system for measuring the aerodynamic forces and an array of platinum thin-film gauges deposited on thermally insulating backing material flush mounted on the model surface is used for convective surface heat transfer measurement in the investigations. The measured value of the drag coefficient varies by about ± 6% from the theoretically estimated value based on the modified Newtonian theory, while the axi-symmetric Navier-Stokes computations overpredict the drag coefficient by about 9%. The normalized values of measured heat transfer rates at 0‡ angle of attack are about 11% higher than the theoretically estimated values. The aerodynamic and the heat transfer data presented here are very valuable for the validation of CFD codes used for the numerical computation of flow fields around hypersonic vehicles.     

Structural and electrical properties of InSe polycrystalline films and diode fabrication

Polycrystalline InSe diode structures, which have been known as a phase-change material, were studied for the first time where the current–voltage characteristics show high potential for data storage application. Highly oriented InSe films were prepared onto heated quartz substrates using the co-evaporation technique with 20% Se over pressure followed by 1 h annealing at the growth temperature. The films were characterized by X-ray diffraction, Raman spectroscopy and atomic force microscopy. InSe films were found to grow in 3-dimension with a roughness of around 400 nm. Diode structures were fabricated for the first time using these InSe films with both Mo bottom and Pt top electrodes that show large change in the electrical characteristics upon fabrication procedures. Thick InSe films (800 nm) showed Schottky characteristics, yielding a barrier height of approximately 1.0 eV.