Dissimilar metal laser spot joining of steel to aluminium in conduction mode

Dissimilar joining of thin (～1 mm) 6111-T4 aluminium alloy and DC04 uncoated low carbon steel used in automobile structures was carried out using laser spot joining in conduction mode. Two sets of experiments were carried out, using copper and aluminium backing bars, respectively. The welds were produced in overlap configuration with steel on the top. The steel surface was irradiated by the laser, and the heat was conducted through the steel into the aluminium. Temperature at the interface was controlled using the fundamental laser energy parameters so that aluminium melts and wets the steel surface. Reaction between the two metallic alloys resulted in the formation of intermetallic compounds (IMC). The formation pattern of IMC was dependent on the temperature profile and the distribution across the interface and was thicker in the centre of the weld and thinner near the edges. The stoichiometry of the IMC formed was varied across the layer and was principally composed of two different layers of Fe₂Al₅ and FeAl₃. Micro hardness tests were carried out to characterise the IMC layer. Mechanical shear tensile tests showed a maximum joint shear strength of up to 68 % of the shear strength of the aluminium alloy.     

Phase correction for frequency response function measurements

In modal testing, an impulse is often used to excite the structure and a linear transducer is used to measure the response. For these impact tests, two signals are measured: the impulsive force and the vibration response. Any lack of synchronization in the time domain acquisition of the two signals results in a frequency-dependent phase error in the frequency response function, or FRF. However, knowledge of the time delay may be used to correct the corresponding phase error. In this research, tests were conducted to measure the frequency-dependent phase error for a capacitive sensor and a frequency domain technique is proposed to correct the FRF. The method was validated using an FRF measurement of a cylindrical artifact mounted in a milling machine spindle.     

Impact of open dumping of municipal solid waste on soil properties in mountainous region

This paper presents the effect of open dumping of municipal solid waste (MSW) on soil characteristics in the mountainous region of Himachal Pradesh, India. The solid waste of dumpsite contains various complex characteristics with organic fractions of the highest proportions. As leachate percolates into the soil, it migrates contaminants into the soil and affects soil stability and strength. The study includes the geotechnical investigation of dump soil characteristics and its comparison with the natural soil samples taken from outside the proximity of dumpsites. The geochemical analysis of dumpsite soil samples was also carried out by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Visual inspection revealed that the MSW consists of high fraction of organics, followed by paper. The soil samples were collected from five trial pits in the dumpsites at depths of 0.5 m, 1 m and 1.5 m. Then the collected soil samples were subjected to specific gravity test, grain size analysis, Atterberg's limit test, compaction test, direct shear test, California bearing ratio (CBR) test and permeability analysis. The study indicated that the dumpsite soils from four study regions show decreasing trends in the values of maximum dry density (MDD), specific gravity, cohesion and CBR, and increasing permeability as compared to the natural soil. The results show that the geotechnical properties of the soils at all four study locations have been severely hampered due to contamination induced by open dumping of waste.     

MWCNT reinforced Polyamide-6,6 films: preparation,characterization and properties

Composite films of Polyamide-6,6 (PA66) and multi-walled carbon nanotubes (MWCNTs) were prepared by a combination of solution casting followed by compression molding techniques. Both unfunctionalized (u-MWCNTs) and functionalized nanotubes (f-MWCNTs) were used in this study. The functionalization involved direct solvent-free amination of MWCNTs with hexamethylenediamine. Thermogravimetric analysis was used to observe the changes in the nanotubes upon functionalization and morphological features of the resulting composite films were studied using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The crystallinity changes by incorporation of the u-MWCNTs and f-MWCNTs in the PA66 matrix were studied by wide angle X-ray scattering and differential scanning calorimetry. The f-MWCNT/PA66 film showed an improvement of ∼43% in maximum tensile stress (MTS) and ∼32% in Young’s modulus over pristine PA66 film, while at a similar loading of 0.5 wt%, the f-MWCNT/PA66 film showed ∼15% increase in MTS and ∼16% increase in modulus over the u-MWCNT/PA66 film. Dynamic mechanical analysis indicated significant difference in the small-strain mechanical properties between the MWCNT-filled and unfilled PA66 at the very low MWNT loadings that were tested and supported the tensile results. The water absorption trend of the composite films showed dramatic improvement over the neat film.     

Plasmon‐Enhanced Spectroscopies with Shell‐Isolated Nanoparticles

Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS), due to its versatility, has been able to break the long‐term limitations of the material‐ and substrate‐specific generalities in the traditional field of surface‐enhanced Raman spectroscopy. With a shell‐isolated work principle, this method provides an opportunity to investigate successfully in surface, biological systems, energetic materials, and environmental sciences. Both the shell material and core morphology are being improved continuously to meet the requirements in diverse systems, such as the electrochemical studies at single crystal electrode surfaces, in situ monitoring of photoinduced reaction processes, practical applications in energy conversion and storage, inspections in food safety, and the surface‐enhanced fluorescence. Predictably, the concept of shell‐isolated nanoparticle‐enhancement could be expanded to the wider range for the performance of plasmon‐enhanced spectral modifications.     

Structural and dielectric relaxor properties of A-site deficient samarium-doped (Ba1−x Sm2x/3)(Zr0.3Ti0.7O3) ceramics

Rare earth samarium (Sm)-doped barium zirconate titanate (Ba_1?x Sm_2x/3)(Zr_0.3Ti_0.7)O₃ (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared using solid state reaction (SSR) route. The structural and microstructural characterizations of the materials were done by using X-ray diffraction and SEM analysis, respectively. Rietveld refinement technique employed to investigate the details of crystal structure revealed single-phase cubic perovskite structure belonging to space group Pm-3m. Microstructure of the doped ceramics were found to be porous and of irregular shape and size along with aggregative characteristic. FTIR technique was employed to study the influence of additives in ceramics compositions and to investigate the displacement of M–O bonds. Raman spectroscopic study revealed that the substitution of Ba²⁺ ions by Sm³⁺ ions shifted the Raman-active modes toward higher energy, which indicated that these materials undergo an increase in average cubicity with increase in Sm³⁺ ion concentration. The temperature dependence of dielectric properties was investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurement indicated a diffuse type of phase transition (DPT). The broadening in the dielectric permittivity and frequency dependence behavior with increase in frequency indicated a relaxor behavior of these materials. The relaxation strength of these materials was well adjusted by using the Vogel–Fulcher relation.     

Synthesis, characterization, photophysical properties of a novel organic photoswitchable dyad in its pristine and hybrid nanocomposite forms

In the present paper the method of synthesis and characterization of a novel organic dyad, 3-(1-Methoxy-3,4-dihydro-naphthalyn-2-yl-)-1-p-chlorophenyl propenone, have been reported. In this paper our main thrust is to fabricate new hybrid nanocomposites by combining the organic dyad with different noble metals, semiconductor nanoparticle and noble metal-semiconductor core/shell nanocomposites. In this organic dyad, donor part is 1-Methoxy-3, 4-dihydro-naphthalen-2-carboxaldehyde with the acceptor p-chloroacetophenone. We have carried out steady state and time-resolved spectroscopic measurements on the dyad and its hybrid nanocomposite systems. Some quantum chemical calculations have also been done using Gaussian 03 software to support the experimental findings by theoretical point of view. Both from the theoretical predictions and NMR studies it reveals that in the ground state only extended (E-type or trans-type) conformation of the dyad exists whereas on photoexcitation these elongated conformers are converted into folded forms (Z- or cis-type) of the dyad, showing its photoswitchable character. Time resolved fluorescence spectroscopic (fluorescence lifetime by TCSPC method) measurements demonstrate that in chloroform medium all the organic-inorganic hybrid nanocomposites, studied in the present investigation, possess larger amount of extended conformers relative to folded ones, even in the excited singlet state. This indicates the possibility of slower energy destructive charge recombination rates relative to the rate processes associate with charge-separation within the dyad. It was found that in CHCl3 medium, the computed charge separation rate was found to be approximately 10(8) s(-1) for the dyad alone and other hybrid nanocomposite systems. The rate is found to be faster than the energy wasting charge recombination rate approximately 10(2)-10(1) s(-1), as observed from the transient absorption measurements for the corresponding hybrid systems. It indicates the conformational geometry has a great effect on the charge-separation and recombination rate processes. The suitability for the construction of efficient light energy conversion devices especially with Ag-Dyad nanocomposite of all the systems studied here is hinted from the observed long ion-pair lifetime.     

Symmetric coupling of multi‐zone curved Galerkin boundary elements with finite elements in elasticity

The coupling of Finite Element Method (FEM) with a Boundary Element Method (BEM) is a desirable result that exploits the advantages of each. This paper examines the efficient symmetric coupling of a Symmetric Galerkin Multi‐zone Curved Boundary Element Analysis method with a Finite Element Method for 2‐D elastic problems. Existing collocation based multi‐zone boundary element methods are not symmetric. Thus, when they are coupled with FEM, it is very difficult to achieve symmetry, increasing the computational work to solve the problem. This paper uses a fully Symmetric curved Multi‐zone Galerkin Boundary Element Approach that is coupled to an FEM in a completely symmetric fashion. The symmetry is achieved by symmetrically converting the boundary zones into equivalent ‘macro finite elements’, that are symmetric, so that symmetry in the coupling is retained. This computationally efficient and fast approach can be used to solve a wide range of problems, although only 2‐D elastic problems are shown. Three elasticity problems, including one from the FEM‐BEM literature that explore the efficacy of the approach are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

A coupling of multi‐zone curved Galerkin BEM with finite elements for independently modelled sub‐domains with non‐matching nodes in elasticity

When the different parts of a structure are modelled independently by BEM or FEM methods, it is sometimes necessary to put the parts together without remeshing of the nodes along the part interfaces. Frequently the nodes do not match along the interface. In this work, the symmetric Galerkin multi‐zone curved boundary element is a fully symmetric formulation and is the method used for the boundary element part. For BEM–FEM coupling it is then necessary to interpolate the tractions in‐between the non‐matching nodes for the FEM part. Finally, the coupling is achieved by transforming the finite element domains to equivalent boundary element domains in a block symmetric formulation. This system is then coupled with a boundary element domain with non‐matching nodes in‐between. Copyright © 2004 John Wiley & Sons, Ltd.