Melting and crack growth in electrical conductors subjected to short-duration current pulses

In this paper, we examine the response of a crack tip in an electrically conducting material subjected to a combination of mechanical load as well as a high density electrical current. We present a detailed examination of the process of evolution of melting and ejection, as revealed by high speed photography. The critical mechanical and electrical parameters that govern crack extension are then determined for two different alloys. Finally, we present an evaluation of the phenomenon through a coupled field simulation to examine the nature of the interaction between the electric field and the thermo-mechanical response.     

Erosion Wear Response of Glass Microsphere Coatings: Parametric Appraisal and Prediction Using Taguchi Method and Neural Computation

This article presents an analysis of the erosion wear response of borosilicate glass microsphere (BGM)-coated metal specimens subjected to reproducible erosive situations. The coatings are deposited on metal substrates by a plasma spraying route using an atmospheric plasma spray setup working on a nontransferred arc mode. The response of these coatings to solid particle erosion for different test parameters is studied. The erosion test schedule is planned as per Taguchi's experimental design and is carried out under controlled laboratory conditions using an air jet–type erosion tester. The analysis of test results reveals that the impact velocity is the most significant among various factors influencing the erosion wear rate of these coatings. A prediction tool based on artificial neural networks (ANNs) is then implemented to predict the triboperformance of such coatings in regard to their erosion rates under different test conditions. ANN is a technique that takes into account the training, testing, and validation protocols using the database generated from experimentation. This technique helps in saving time and resources for a large number of experimental trials and it is seen in this work that it can successfully predict the wear rate of the coatings for test conditions both within and beyond the experimental domain.     

Structural, dielectric and ferroelectric properties of multilayer lithium tantalate thin films prepared by sol-gel technique

Multilayer lithium tantalate thin films were deposited on Pt-Si [Si(111)/SiO₂/TiO₂/Pt(111)] substrates by sol-gel process. The films were annealed at different annealing temperatures (300, 450 and 650 °C) for 15 min. The films are polycrystalline at 650 °C and at other annealing conditions below 650 °C the films are in amorphous state. The films were characterized using X-ray diffraction, atomic force microscopy (AFM) and Raman spectroscopy. The AFM of images show the formation of nanograins of uniform size (50 nm) at 650 °C. These polycrystalline films exhibit spontaneous polarization of 1.5 μC/cm² at an application of 100 kV/cm. The dielectric constant of multilayer film is very small (6.4 at 10 kHz) as compared to that of single crystal.     

Viscoelastic interpretations of erosion performance of short aramid fibre reinforced vinyl ester resin composites

Short aramid fibre reinforced vinyl ester resin based isotropic composites are fabricated with varying fibre weight fractions (20–50 wt%). The composites were evaluated for their erosion performance under a dynamic set of variables such as impingement angle (30°–90°), impact velocity (43–76 m/s), erodent size (250–600 μm) and stand-off distance (55–85 mm) following design of experiments (DOE) based on Taguchi analysis approach. The thermo-mechanical attributes such as storage modulus, loss modulus and damping properties as viscoelastic responses of the composites were investigated in the temperature range of 0–180 °C for their possible interpretations regarding reinforcement efficiency and energy dissipation aspects relevant to erosion process. An interrelation between the full-width half-maxima (FWHM) of loss modulus peak and erosion rate has emerged indicating the erosion to be mainly controlled by the fibre–matrix interfacial characteristics. The eroded surface morphology investigation by scanning electron microscopy (SEM) revealed the nature of wear-craters, material damage mode and other qualitative attributes responsible in facilitating erosion of the composites.     

Morphological interpretations and micromechanical properties of polyamide-6/polypropylene-grafted-maleic anhydride/nanoclay ternary nanocomposites

Ternary nanocomposites were fabricated based on an optimized impact modified polyamide-6 (PA-6)/polypropylene grafted maleic anhydride (PP-g-MA) blend composition with varied concentrations (0–6 wt.% at a step of 2 wt.%) of organoclay, Cloisite 30B™. The morphological attributes such as state of intercalation/exfoliation/crystalline organization and fractured surface topography of the nanocomposites were characterized by transmission electron microscopy (TEM), wide angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) while the thermal characterizations were done by conducting differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The WAXD/DSC studies have revealed that the crystallinity of the nanocomposites remained unaffected. DMA revealed an increase in glass transition temperature (T_g) of the nanocomposites by ∼14–19 °C relative to the soft polypropylene (PP)-phase, by ∼7–12 °C relative to the neat matrix PA-6 and by ∼4–9 °C relative to the optimized impact toughened PA-6 matrix while simultaneously being accompanied by the appearance of a second phase T_g peak progressively at higher temperatures as a function of nanoclay content, indicating the reinforcement effects/restrictions imposed by the nanoclay layers to the polymer chain mobility. The bulk mechanical response of the nanocomposites such as tensile, flexural and impact properties were studied and its related micromechanics aspects have been investigated using composite theories such as Halpin-Tsai, Hui-Shia, Takayanagi and Pukanszky models to analyze the interfacial effects and its role on the stress transfer efficiency. SEM analysis of fractured surface indicated that the failure mode of the nanocomposites undergoes a switch-over from interfacial-effects assisted fibrillation controlled ductile deformation to nanoclay induced soft PP-phase stiffened semi-ductile response via shear-lips formation.