Acoustic emission source location and damage detection in a metallic structure using a graph-theory-based geodesic pproach

A geodesic-based approach using Lamb waves is proposed to locate the acoustic emission (AE) source and damage in an isotropic metallic structure. In the case of the AE (passive) technique, the elastic waves take the shortest path from the source to the sensor array distributed in the structure. The geodesics are computed on the meshed surface of the structure using graph theory based on Dijkstra's algorithm. By propagating the waves in reverse virtually from these sensors along the geodesic path and by locating the first intersection point of these waves, one can get the AE source location. The same approach is extended for detection of damage in a structure. The wave response matrix of the given sensor configuration for the healthy and the damaged structure is obtained experimentally. The healthy and damage response matrix is compared and their difference gives the information about the reflection of waves from the damage. These waves are backpropagated from the sensors and the above method is used to locate the damage by finding the point where intersection of geodesics occurs. In this work, the geodesic approach is shown to be suitable to obtain a practicable source location solution in a more general set-up on any arbitrary surface containing finite discontinuities. Experiments were conducted on aluminum specimens of simple and complex geometry to validate this new method.

A green protocol for room temperature synthesis of silver nanoparticles in seconds

We describe here a rapid, energy-efficient, green and economically scalable room temperature protocol for the synthesis of silver nanoparticles. Tannic acid, a polyphenolic compound derived from plant extracts is used as the reducing agent. Silver nanoparticles of mean size ranging from 3.3 to 22.1 nm were synthesized at room temperature by the addition of silver nitrate to tannic acid solution maintained at an alkaline pH. The mean size was tuned by varying the molar ratio of tannic acid to silver nitrate. We also present proof of concept results demonstrating its suitability for room temperature continuous flow processing.

Phthalocyanine macrocycle as stabilizer for gold and silver nanoparticles

A one-step process was used for the preparation of gold and silver nanoparticles stabilized by an aminophthalocyanine macrocycle. The resultant nanoparticles were characterized by absorption spectra, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The nanoparticles were found to possess relatively narrow size distribution. The gold nanoparticles have an average diameter of similar to 2 nm, while silver particles have 4-5 nm. Preliminary studies on fluorescence and surface enhanced Raman spectroscopy were carried out using these nanoparticles. Fluorescence studies indicate that gold nanoparticles do not quench the fluorescence, while silver nanoparticles do. The stabilized nanoparticles showed enhancement of the Raman signals, thus revealing that they are good substrates for surface enhanced Raman scattering studies.

Mixed mode (I and II) crack tip fields in bulk metallic glasses

Stationary crack tip fields in bulk metallic glasses under mixed mode (I and II) loading are studied through detailed finite element simulations assuming plane strain, small scale yielding conditions. The influence of internal friction or pressure sensitivity on the plastic zones. notch deformation, stress and plastic strain fields is examined for different mode mixities. Under mixed mode loading, the notch deforms into a shape such that one part of its surface sharpens while the other part blunts. Increase in mode If component of loading dramatically enhances the normalized plastic zone size, lowers the stresses but significantly elevates the plastic strain levels near the notch tip. Higher internal friction reduces the peak tangential stress but increases the plastic strain and stretching near the blunted part of the notch. The simulated shear bands are straight and extend over a long distance ahead of the notch tip under mode II dominant loading. The possible variations of fracture toughness with mode mixity corresponding to failure by brittle micro-cracking and ductile shear banding are predicted employing two simple fracture criteria. The salient results from finite element simulations are validated by comparison with those from mixed mode (I and II) fracture experiments on a Zr-based bulk metallic glass.

Fabrication and Phase Transformation in Crystalline Nanoparticles of PbZrO3 Derived By Sol-Gel

In this research fabrication of crystalline PbZrO3 (PZ) nanoparticles and their phase transformation behavior is investigated. A novel sol-gel method was used for the synthesis of air-stable and precipitate-free diol-based sol of PZ, which was dried at 150 degrees C and then calcined at 300-700 degrees C for 1 h. The morphology, crystallinity and phase formation of as synthesized nanoparticles were studied by the selected-area electron diffraction (SAED), X-ray diffraction (XRD), thermal gravimetric analysis/differential scanning calorimetry (TGA-DSC), and high resolution transmission electron microscope (HRTEM). The XRD, SAED, and TGA-DSC analyses confirmed the tetragonal lead rich zirconia phase (t-Z phase) and monoclinic zirconia phase (m-Z phase) as the intermediate phases during the calcinations process followed by crystallization of single orthorhombic PZ phase at about 700 degrees C. The average PZ particle size was observed about 20 nm as confirmed by TEM study. Energy-dispersive X-ray spectroscopy (EDX) analysis demonstrated that stoichiometric PbZrO3 was formed.

Time reversal technique for health monitoring of metallic structure using Lamb waves

Time reversal active sensing using Lamb waves is investigated for health monitoring of a metallic structure. Experiments were conducted on an aluminum plate to study the time reversal behavior of A(0) and S-0 Lamb wave modes under narrow band and broad band pulse excitation. Damage in the form of a notch was introduced in the plate to study the changes in the characteristics of the time reversed Lamb wave modes experimentally. Time-frequency analysis of the time reversed signal was carried out to extract the damage information. A measure of damage based on wavelet transform was derived to quantify the hidden damage information in the time reversed signal. It has been shown that time reversal can be used to achieve temporal recompression of Lamb waves under broadband signal excitation. Further, the broad band excitation can also improve the resolution of the technique in detecting closely located defects. This is demonstrated by picking up the reflection of waves from the edge of the plate, from a defect close to the edge of the plate and from defects located near to each other. This study shows the effectiveness of Lamb wave time reversal for temporal recompression of dispersive Lamb waves for damage detection in health monitoring applications. (C) 2009 Elsevier B.V. All rights reserved.

Dependence of pH and surfactant effect in the synthesis of magnetite(Fe3O4) nanoparticles and its properties

Nanoparticles of Fe3O4 were synthesized by co-precipitation in an aqueous solution containing ferrous and ferric salts (1:2) at varying pH with ammonia as a base. It was found that the value of pH influences the reaction mechanism for the formation of Fe3O4. Furthermore, the addition of mercaptoethanol significantly reduced the crystalline size of Fe3O4 nanoparticles from 15.03 to 8.02 nm. X-ray diffraction (XRD) spectra revealed that the synthesized nanoparticles were epsilon-Fe2O3 or Fe3O4 phase. To further prove the composition of the product, as-prepared Fe3O4 were examined by X-rayphotoelectron spectroscopy (XPS). Magnetic properties of the obtained particles were determined by vibrating sample magnetometer (VSM). Further analysis of the X-ray studies shows that while maintaining a pH value of 6 and 9 in a solution containing iron salts II and III ions produces epsilon-Fe2O3. Whereas a pH value of 11 produces magnetite (Fe3O4) phase. All of these results show that the pH has a major role in the observed phase formation of (Fe3O4) nanoparticles.

Separation of Metallic and Semiconducting Single-Walled Carbon Nanotubes Through Fluorous Chemistry

Separation of metallic from semiconducting single-walled carbon nanotubes has been a major challenge for some time and some previous efforts have resulted in partial success. We have accomplished the separation effectively by employing fluorous chemistry wherein the diazonium salt of 4-heptadecafluorooc tylaniline selectively reacts with the metallic nanotubes present in the mixture of nanotubes. The resulting fluoroderivative was extracted in perfluorohexane leaving the semiconducting nanotubes in the aqueous layer. The products have been characterized by both Raman and electronic absorption spectroscopy. The method avoids the cumbersome centrifugation step required by some other procedures.

Microtribology and Friction-Induced Material Transfer in Layered MoS2 Nanoparticles Sprayed on a Steel Surface

Frictional performance of molybdenum disulfide (MoS2) particles sprayed on a substrate is investigated in a ball-on-disc tribometer. The ability of large (similar to 2 mu m) and small (similar to 50 nm) particles to generate low-friction transfer film is investigated with a view to elucidate the requirement for film formation. Particle migration, particle stability in the contact region, oxidation potential, and particle adhesion to the substrate are explored within a span of operating parametersp; normal load, and sliding velocity. It is found that the larger particles are able to migrate to the contact to raise a homogeneous but nonuniform low-friction transfer film that flows plastically to yield large contact areas, which aid in wear protection. Within the present load and speed range, the inability of small particles to stay in the contact region and undergo basal slip militates against the formation of a low-friction transfer film.

Novel synthesis of superparamagnetic Ni-Co-B nanoparticles and their effect on superconductor properties of MgB2

A new procedure for the preparation of amorphous Ni-Co-B nanoparticles is reported, with a detailed investigation of their morphology by X-ray diffraction and transmission electron microscopy, as well as their magnetic properties. Many factors, such as chemical composition, anisotropy, size and shape of the particles, were controlled through chemical synthesis, resulting in the control of morphological and magnetic properties of the nanoparticles. Controlling pH values with ethylenediamine and using sodium dodecyl sulfate surfactant lowered the size of the nanoparticles to below 10 nm. Such a small structure and chemical disorder in nanocrystalline materials lead to magnetic properties that are different from those in their bulk-sized counterparts. The obtained nanoparticles can be used for different purposes, from pharmaceutical applications to implementations in different materials technology. The focus of this research is the synthesis of Ni-Co-B nanoparticles in a new way and studying the reaction of Ni-Co-B nanoparticles with Mg and B precursors and their effect on MgB2 properties. New nanostructures are formed in the reaction of Ni-Co-B nanoparticles with Mg: Mg2Ni, Co2Mg and possibly Mg2Co.

Platinum dendritic nanoparticles with magnetic behavior

Magnetic nanoparticles have attracted increasing attention for biomedical applications in magnetic resonance imaging, high frequency magnetic field hyperthermia therapies, and magnetic-field-gradient-targeted drug delivery. In this study, three-dimensional (3D) platinum nanostructures with large surface area that features magnetic behavior have been demonstrated. The well-developed 3D nanodendrites consist of plentiful interconnected nano-arms ∼4 nm in size. The magnetic behavior of the 3D dendritic Pt nanoparticles is contributed by the localization of surface electrons due to strongly bonded oxygen/Pluronic F127 and the local magnetic moment induced by oxygen vacancies on the neighboring Pt and O atoms. The magnetization of the nanoparticles exhibits a mixed paramagnetic and ferromagnetic state, originating from the core and surface, respectively. The 3D nanodendrite structure is suitable for surface modification and high amounts of drug loading if the transition temperature was enhanced to room temperature properly.

Bio-inspired multifunctional metallic foams through the fusion of different biological solutions

Nature is a school for scientists and engineers. Inherent multiscale structures of biological materials exhibit multifunctional integration. In nature, the lotus, the water strider, and the flying bird evolved different and optimized biological solutions to survive. In this contribution, inspired by the optimized solutions from the lotus leaf with superhydrophobic self-cleaning, the water strider leg with durable and robust superhydrophobicity, and the lightweight bird bone with hollow structures, multifunctional metallic foams with multiscale structures are fabricated, demonstrating low adhesive superhydrophobic self-cleaning, striking loading capacity, and superior repellency towards different corrosive solutions. This approach provides an effective avenue to the development of water strider robots and other aquatic smart devices floating on water. Furthermore, the resultant multifunctional metallic foam can be used to construct an oil/water separation apparatus, exhibiting a high separation efficiency and long-term repeatability. The presented approach should provide a promising solution for the design and construction of other multifunctional metallic foams in a large scale for practical applications in the petro-chemical field. Optimized biological solutions continue to inspire and to provide design idea for the construction of multiscale structures with multifunctional integration. Inspired by the optimized biological solutions from the lotus leaf with superhydrophobic self-cleaning, the water strider leg with durable and robust superhydrophobicity, and the lightweight bird bone with hollow structures, multifunctional metallic foams with multiscale structures are fabricated, demonstrating low adhesive superhydrophobic self-cleaning, striking loading capacity, stable corrosion resistance, and oil/water separation.

A universal relation for the cohesive energy of nanoparticles

A universal relation between the cohesive energy and the particle size has been predicted based on the liquid-drop model. The universal relation is well supported by other theoretical models and the available experimental data. The universal relations for intermediate size range as well as for particles with very few atoms are discussed. A comparison of onset temperature of evaporation also establishes a universal relation.

CAE-based prediction of projectile residual velocity for impact on single and multi-layered metallic armour plates

The present, paper deals with the CAE-based study Of impact of jacketed projectiles on single- and multi-layered metal armour plates using LS-DYNA. The validation of finite element modelling procedure is mainly based on the mesh convergence study using both shell and solid elements for representing single-layered mild steel target plates. It, is shown that the proper choice of mesh density and the strain rate-dependent material properties are essential for all accurate prediction of projectile residual velocity. The modelling requirements are initially arrived at by correlating against test residual velocities for single-layered mild steel plates of different depths at impact velocities in the ran.-c of approximately 800-870 m/s. The efficacy of correlation is adjudged, in terms of a 'correlation index', defined in the paper: for which values close to unity are desirable. The experience gained for single-layered plates is next; used in simulating projectile impacts on multi-layered mild steel target plates and once again a high degree of correlation with experimental residual velocities is observed. The study is repeated for single- and multi-layered aluminium target plates with a similar level of success in test residual velocity prediction. TO the authors' best knowledge, the present comprehensive study shows in particular for the first time that, with a. proper modelling approach, LS-DYNA can be used with a great degree of confidence in designing perforation-resistant single and multi-layered metallic armour plates.

Free-volume dependent pressure sensitivity of Zr-based bulk metallic glass

Instrumented indentation experiments on a Zr-based bulk metallic glass (BMG) in as-cast, shot-peened and structurally relaxed conditions were conducted to examine the dependence of plastic deformation on its structural state. Results show significant differences in hardness, H, with structural relaxation increasing it and shot peening markedly reducing it, and slightly changed morphology of shear bands around the indents. This is in contrast to uniaxial compressive yield strength, sigma(y), which remains invariant with the change in the structural state of the alloys investigated. The plastic constraint factor, C = H/sigma(y), of the relaxed BMG increases compared with that of the as-cast glass, indicating enhanced pressure sensitivity upon annealing. In contrast, C of the shot-peened layer was found to be similar to that observed in crystalline metals, indicating that severe plastic deformation could eliminate pressure sensitivity. Microscopic origins for this result, in terms of shear transformation zones and free volume, are discussed.