B.S.S. Daniel

Thermal Relaxation and High Temperature Creep of Zr55Cu30Al10Ni5 Bulk Metallic Glass

The free volume model is applied to isothermal relaxation and hightemperature creep. For this analysis, the time dependent flow behaviourof Zr55Cu30Al10Ni5 bulk metallic glass (BMG) near the glass transition temperature (Tg) is expressed as a trade off between stress inducedgeneration and diffusion controlled annihilation of free volume. Thestrain rate-stress relation over a wide strain rate-range (10−7to 10−2 s−1) was established for three different temperatures near Tg. It was found that the thermal relaxation behaviour and creep kinetics arecontrolled by the mobility of atoms with an activation energy of 161 kJ/mol.

Aluminum Melt Foam Processing for Light-Weight Structures

Aluminum foam was prepared by two routes, namely, gas injection technique and by the decomposition of TiH2 blowing agent. The foam structure can be largely controlled by the amount of degassing agent and duration of foaming. The heterogeneity in cell structure could be explained on the basis of foam stability, drainage in the cell walls, and heat transfer during quenching. The variation in cell size and drainage is negligible when the holding time is around 120 s at 750°C. The constant strain rate compression tests indicate that the Youngs modulus, plateau stress, and energy absorption capacity increases with relative density of the foam, while the densification strain reduces with increase in relative density.

Optimization of short Indian Areca fruit husk fiber (Areca catechu L.)–reinforced polymer composites for maximizing mechanical properties

ABSTRACT Natural fibers are being used as reinforcing materials for polymer composites due to their eco-friendly properties. Areca fruit husk fiber (AFHF) is one such fiber; it is currently discarded waste from the tobacco industry, but has huge potential. It is light in weight with a perforated surface that enables good bonding with a polymer matrix. In this study, comprehensive characterization of physical, chemical, thermal, mechanical, and microstructural properties was carried out on the fiber and the composite made with that fiber to optimize the fiber content. The optimum fiber content is found to be 40 wt.%, whereas beyond that, fiber pull-out and debonding reduces the load-bearing capacity of the composite. The specific properties of AFHF polymer composite are even higher than that of the popular E-glass fiber composite, which positions AFHF composite as an alternative structural material.

Nickel aluminide reinforced AlN/Al composites by pressureless infiltration

The reactive infiltration of nickel aluminide powder preform at temperatures above 700°C yielded dense composites. The microstructural evolution of the constituent phases at different processing temperatures are interpreted via the vacancy diffusion mechanism and the peritectic reaction occurring at 854°C. Optimum mechanical properties were obtained for composites processed at lower temperatures.

Critical Parameters Affecting Mechanical Behavior of Natural Fiber Reinforced Plastics

ABSTRACT Of the numerous special properties of natural fiber composites, light weight and biodegradability are the most attractive. Also, natural fiber reinforced composites have sufficiently good mechanical properties. In the present research investigation, the mechanical properties of the natural fiber (nettle and grewia optiva fiber) reinforced thermoset and thermoplastic composites have been evaluated and compared. The morphological analysis of the fractured test specimens subjected to different types of mechanical loading has also been performed using scanning electron microscopy (SEM). Critical parameters, such as contact angle of polymers, surface roughness of the natural fibers, and twist angle of the natural fiber yarn have been evaluated in order to emphasize their importance in defining the mechanical behavior of the developed composite laminates. The results reveal that poly-lactic acid (PLA)-based natural fiber composites have superior mechanical properties as compared to the polypropylene (PP)- and epoxy-based natural fiber composites.

Cellulose powder treatment on Cissus quadrangularis stem fiber-reinforcement in unsaturated polyester matrix composites

Natural fibers from bio-renewable sources have the potential to be used as an alternate reinforcement for the perilous synthetic fibers. The hazards of prolong exposure to such fibers are quite serious, which demands scientific intervention. Natural fibers, like the one investigated – Cissus quadrangularis stem fiber (CQSF), have proven thermomechanical properties for polymer composite reinforcement. Enhancing fiber–matrix bonding through chemical treatments such as mercerization and deposition of cotton linters-based microcrystalline cellulose powder on fiber surface are comprehensively investigated. The mechanical properties of treated fiber composites reveal good bonding features through scanning electron microscopy analysis, which are further substantiated by the evaluation of mechanical property. In particular, 5 wt.% cellulose powder-treated CQSF/polyester composites showed distinguishable enrichment in mechanical and water absorption characteristics.

Unified theory of deformation for structural superplastics, metallic glasses and nanocrystalline materials

A rate equation for grain/interphase boundary sliding is developed which is able to accurately account for the deformation of structural superplastics, metallic glasses and nanostructured materials on a common physical basis. In some structural superplastics, however, at the highest strain rates dislocation climb controlled creep becomes important. In its present state of development, the model for the optimal range is able to predict all the three constants of the rate equation ab initio if the grain size is uniform and constant, the grain shape is simple, e.g., rhombic dodecahedron and the number of grain boundaries that participate in a mesoscopic boundary sliding event is known from experiments. When a grain size distribution is present and the grain shape is not regular, the grain size exponent in the rate equation will have to be obtained empirically (in addition to the number of boundaries involved in a mesoscopic sliding event). Understanding of behaviour in the region where grain deformation co-exits with grain boundary flow is phenomenological at present.

Modeling Mechanical Milling Process for Synthesis of Graphite Nanoparticles and their Characterization

The synthesis of graphite nanoparticles at ambient temperature by high energy mechanical milling is modelled using ANN (Artificial Neural Network). The effect of milling time on the evolution of particle size, inclusion, microstructure and morphology were examined using XRD (X-Ray Diffraction), EDS (Energy Dispersive X-Ray Spectroscopy), SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscope). ANN was effectively used to predict the influence of milling time on particle size and to forecast the milling time for the formation of nanoparticles. XRD results of investigation revealed change in strain behaviour of graphite particles of different sizes when heat treated.

Application of Graphene Oxide and TiO2 in the Fabrication of Dye Sensitized Solar Cells Module by Electrode Modification

The use of graphene oxide nanosheets as a counter-electrode material substituting platinum in dye-sensitized solar cell (DSSC) shows the cheap way of fabricating DSSC with increase in conversion efficiency. The incorporation of graphene oxide in active electrode was increased the conversion efficiency of DSSC significantly. The DSSC was fabricated, consists of graphene-TiO2 as an active electrode and compared to cell only consist of TiO2 as an active electrode, while using carbon as a counter electrode. The DSSC fabricated with electrolyte solution and organic dye, and then they were tested for their photovoltaic performance.

Synthesis of TiO2 Film for Dye-Sensitized Solar Cells

Mesoporous solid TiO2 film (2-50nm) offering large specific surface area and well connected cavities have been researched extensively in the last decade, aiming to enhance photo-conversion efficiency in the dye-sensitised solar cells (DSSCs). The efficiency of DSSCs is highly sensitive to surface morphology, crystallinity and porosity of the TiO2 film which are in turn dependent upon processing temperature. Multilayered porous TiO2 films were synthesised under different temperature regimes using sol-gel method in combination with spin coating. The influence of temperature variation on the films morphology, crystallinity, and its interfacial adhesiveness to the substrate was studied. A modified method of pre-curing temperature was employed, in order to attain firm adhesiveness of the film to the Fluorine-doped Tin Oxide (FTO) glass substrate. The films prepared by different pre-curing temperature protocols were incorporated into DSSCs for evaluating the affect of varying temperature on photo-conversion efficiency of the cells.