The impact behavior of aluminum alloy 6061: Effects of notch severity

In this paper the influence of notch acuity and test temperature on the impact behavior of aluminum alloy 6061 is presented and discussed. Notch angles of 45°, 60°, 75° and 90° were chosen for a standard charpy impact test specimen containing two such notches positioned at right angles to the applied load. For a given angle of the notch the dynamic fracture toughness increased with an increase in test temperature. At a given test temperature, the impact toughness of a ductile microstructure decreased with an increase in notch severity. For the least severe notch dynamic fracture surfaces revealed the occurrence of localized mixed-mode deformation at the elevated temperature. An increase in notch severity resulted in essentially Mode-I dominated fracture at all test temperatures. The results are discussed in light of alloy microstructure, fracture mechanisms and deformation field ahead of the advancing crack tip.     

Influence of notch severity on the impact fracture behavior of aluminum alloy 7055

In this paper, the conjoint influence of notch severity and test temperature on the impact behavior of an Al-Zn-Mg-Cu alloy 7055 in the T7751 microstructural condition is presented and discussed. Notch angles of 45°, 75° and 90° were chosen for a standard charpy impact test specimen containing two notches. For a given angle of the notch the increase in dynamic fracture toughness, with test temperature, is most significant for the least severe of the notches, i.e. 45°. At a given test temperature, the impact toughness of the T7751 microstructure decreased with an increase in notch severity. An increase in notch severity resulted in essentially Mode I dominated fracture at all test temperatures. The influence of localized mixed-mode loading is minimal for the alloy has low dynamic toughness. The impact fracture behavior of the alloy is discussed in light of alloy microstructure, mechanisms governing fracture and the deformation field ahead of a propagating crack.     

Nondestructive characterisation of MOX fuel rods using gamma autoradiography (GAR)

During the fabrication of mixed uranium-plutonium oxide (MOX) fuel rods, two important characteristics to be checked in as-fabricated fuel pins are plutonium enrichment and plutonium dioxide agglomerates. The mixed oxide fuel pellets are made via mechanical mixing of uranium dioxide and plutonium dioxide powders by cold compaction and sintering. The chance of loading a wrong Pu enrichment pellet and having pellets with plutonium dioxide agglomerates in a fuel pin cannot be ruled out. A simple nondestructive evaluation technique is felt necessary to ensure at the last stage (in the welded pins) to check these two characteristics. During the fabrication of MOX fuel rods for Boiling Water Reactors at Advanced Fuel Fabrication Facility of BARC at Tarapur, Gamma-auto-radiography was successfully used to evaluate composition of MOX pellets and to detect presence of PuO₂ agglomerates in the peripheral region. The fuel pins are allowed to be in contact with industrial X-ray films loaded in cassettes for a long time and the processed films are carefully evaluated. Experiments were made to standardise the conditions for distinguishing fuel pellets of different composition by gamma-auto-radio-graphy of fuel pins loaded with pellets of different composition. Gamma-auto-radiography of fuel pins containing agglomerates of different sizes was also carried out. This paper describes the experimental details of the technique, results obtained and compare with other nondestructive evaluation techniques available.     

Structural transformation and magnetic properties of CaMn1 − xFexO3 − δ (0.0 ≤ x ≤ 0.5)

We have investigated the structural and magnetic properties of CaMn_1 − xFe_xO_3 − δ (0.0 ≤ x ≤ 0.5). Solid state method is used for the synthesis of these samples. Sintering of these compositions at 1300 °C stabilizes higher ionic radii Fe^+ 3 (0.645 Å) at Mn^+ 4 (0.53 Å) site in CaMn_1 − xFe_xO_3 − δ. Structural transformation from orthorhombic to tetragonal to pseudo cubic crystal system and the increase in lattice parameters have been observed with the substitution of Fe at Mn site in CaMn_1 − xFe_xO_3 − δ (0.0 ≤ x ≤ 0.5). The magnetization data show the transformation of G type of antiferromagnetic arrangement of Mn^+ 4 electrons spins in CaMnO₃ into paramagnetic spin type arrangement with the substitution of Fe at Mn site. The compositions x = 0.05, x = 0.1and x = 0.2 show a small kink ~ 100 K in the magnetization data, which resulted due to the competition between antiferromagnetic and paramagnetic states with the Fe substitution.     

Fabrication of polymethyl methacrylate/polysulfone/nanoceramic composites for orthopedic applications

We report the fabrication of polymethyl methacrylate/polysulfone/nanohydroxyapatite (PMMA/PSu/nHA) and PMMA/PSu/nanotitania (PMMA/PSu/nTiO₂) composites using N′N′‐methylene‐bis‐acrylamide (MBA) to crosslink PMMA and act as a blending agent. The composite was made porous by incorporating polyethylene glycol as the pore‐forming agent. The blend between PMMA and PSu was confirmed using Fourier transform infrared spectroscopy and thermogravimetric analysis (TGA). The surface morphology of the composites analyzed using scanning electronic microscopy (SEM) revealed the porous structure and the wide distribution of the fillers that were found to aggregate at higher concentrations. The maximum tensile strength observed for composites was with 5% nHA (23 MPa) and 7.5% TiO₂ (30 MPa). The TGA of the composites showed better thermal stability with increase in the filler concentrations. The X‐ray diffraction analysis showed that appearance of new peaks in the blend polymers indicating a strong interaction between PMMA and PSu. The surface of the composites was coated with amoxicillin and its efficiency was examined by the Zone of Inhibition test using Streptococcus mutans. The bioactivity of the composites was evaluated by immersing them in simulated body fluid and examining their surface for the formation of calcium‐phosphate layer using SEM and EDAX. Bioactivity was found to increase with increase in filler content. The in vitro biocompatibility of the composites, evaluated using monkey kidney epithelial cells by MTT assay showed that the composites containing nHA showed better cell viability than the composites with nTiO₂. The study showed that the composites with nTiO₂ exhibited better strength when compared with nHA composites while the later exhibited better biocompatibility. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Formation and characterization of flame synthesized hexagonal zinc oxide nanorods for gas sensor applications

Highly crystalline ZnO nanorods were synthesized via a simple flame synthesis technique from micro-metallic Zn. The X-ray diffraction analysis confirms presence of zinc oxide nanorods with highly oriented wurtzite structure in which the oxygen atoms are arranged in a hexagonal close packed lattice and zinc atoms occupy half of the tetrahedral sites. The photoluminescence spectrum of the nanorods shows the presence of interstitial vacancy of Zn. Energy dispersive X-ray spectrum reveals oxygen deficiency, which leads to ferromagnetic behavior and gas sensing property of the nanorods.     

The effect of annealing temperature and the characteristics of p-n junction diodes based on sprayed polyaniline/ZnO thin films

Polyaniline,ZnO and polyaniline/ZnO nanocomposite thin films are coated on glass substrates using the spray pyrolysis technique.The samples are characterized by the XRD,SEM,EDAX,UV-Vis and I-V characteristics. The XRD analyses confirm that the spray-coated polyaniline and ZnO thin films have orthorhombic and hexagonal structures,respectively,and optical bandgap energy decreases from 3.81 to 3.41 eV with the addition of a Zn atom.SEM analysis of the polyaniline/ZnO nanocomposite thin films shows that there is an agglomeration of ZnO particles with uniform distribution in the polyaniline matrix,and the diode characteristics of the polyaniline /ZnO nanocomposite show weak rectification behavior.Parameters such as the ideality factor,reverse saturation current and barrier height are calculated from the I-V characteristics.     

Influence of sunflower oil based nanoemulsion (AUSN-4) on the shelf life and quality of Indo-Pacific king mackerel (Scomberomorus guttatus) steaks stored at 20 °C

The influence of nanoemulsion (AUSN-4) on the microbiological, proximal, chemical, and sensory qualities of Indo-Pacific king mackerel (Scomberomorus guttatus) steaks stored at 20 °C was studied for a time period of 72 h. AUSN-4 treatment showed initial reduction (P > 0.05) in the heterotrophic, H₂S and lactic acid bacterial populations in 12 h, followed by a gradual increase in their respective populations. Irrespective of treatments, reduction in total carbohydrate, protein, and fat contents were observed in all samples with an increase in storage time (h), with AUSN-4 treated steaks having the lowest reduction. AUSN-4 treatment significantly (P < 0.05) decreased the values of chemical indicators of spoilage throughout the storage period. Organoleptic evaluation revealed that AUSN-4 treated steaks showed an extension of shelf life of 48 h, when compared with control and antibiotic treated samples, respectively. Based on the results obtained in our present study we conclude that sunflower oil based nanoemulsion preservative technique is able to extend the shelf life and maintain the quality of S. guttatus steaks during storage.     

Modeling and simulation of three phase multilevel inverter for grid connected photovoltaic systems

This paper presents a control for a three phase five-level neutral clamped inverter (NPC) for grid connected PV system. The maximum power point tracking (MPPT) is capable of extracting maximum power from the PV array connected to each DC link voltage level. The MPPT algorithm is solved by fuzzy logic controller. The fuzzy MPPT is integrated with the inverter so that a DC–DC converter is not needed and the output shows accurate and fast response. A digital PI current control algorithm is used to remain the current injected into the grid sinusoidal and to achieve high dynamic performance with low total harmonic distortion (THD). The validity of the system is verified through MATLAB/Simulink and the results are compared with three phase three-level grid connected NPC inverter in terms of THD.