The Effect of Temperature on the Strength of Adhesively-Bonded Composite-Aluminium Joints

Different materials have different coefficients of thermal expansion, which is a measure of the change in length for a given change in temperature. When different materials are combined structurally, as in a bonded joint, a temperature change leads to stresses being set up. These stresses are present even in an unloaded joint which has been cured at say 150°C and cooled to room temperature. Further stresses result from operations at even lower temperatures.

In addition to temperature-induced stresses, account also has to be taken of changes in adhesive properties. Low temperatures cause the adhesive to become more brittle (reduced strain to failure), while high temperatures cause the adhesive to become more ductile, but make it less strong and more liable to creep.

Theoretical predictions are made of the strength of a series of aluminium/CFRP joints using three different adhesives at 20°C and 55°C. Various failure criteria are used to show good correlation with experimental results.     

Green's function approach for modeling of electrostatic effects in nanoscale fully depleted double‐gate silicon‐on‐insulator metal‐oxide‐semiconductor field‐effect transistors

Exact solution of two‐dimensional (2D) Poisson's equation for fully depleted double‐gate silicon‐on‐insulator metal‐oxide‐semiconductor field‐effect transistor is derived using three‐zone Green's function solution technique. Framework consists of consideration of source–drain junction curvature. 2D potential profile obtained forms the basis for estimation of threshold voltage. Temperature dependence of front surface potential distribution, back surface potential distribution and front‐gate threshold voltage are modeled using temperature sensitive parameters. Applying newly developed model, surface potential and threshold voltage sensitivities to gate oxide thickness have been comprehensively investigated. Device simulation is performed using ATLAS 2D (SILVACO, 4701 Patrick Henry Drive, Bldg. Santa Clara, CA 95054 USA) device simulator, and the results obtained are compared with the proposed 2D model. The model results are found to be in good agreement with the simulated data. Copyright © 2013 John Wiley & Sons, Ltd.     

Structural,Mechanical and Dielectric Properties of Microwave-Assisted High-Energy Ball Milling Synthesis of Hydroxyapatite

Abstract

In the present work, the effect of high-energy ball milling (HEBM) of starting precursors of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂)/HA system on the processing temperature, morphological, mechanical, and electrical properties are highlighted. Calcination and sintering of HA system were carried out in microwave furnace. XRD study confirmed the evolution of HA phase and EDX analysis confirmed Ca/P ratio ～1.65. Grain size of HA samples, synthesized by using microwave-assisted HEBM technique was found to be in the order of 54–75?nm. Enhanced dielectric and mechanical properties were obtained in HA samples.     

Study of crystal structure,dielectric, magnetic and magnetoelecrtic properties of xCoFe2O4-(1-x)Na0.5Bi0.5TiO3 composites

Multiferroic composites of spinel ferrite and ferroelectric xCoFe₂O₄ – (1-x)Na_0.5Bi_0.5TiO₃ (with x = 0.10,0.30,0.50) were efficiently prepared by standard solid state reaction mechanism. X-ray diffractometer was used to analyze crystal structure of the prepared composites. The observed XRD patterns of the composites comprise peaks of both the phases i.e. ferrite and ferroelectric, with no sign of secondary peaks. Rietveld refinement of XRD data further confirms the coexistence of these two phases with cubic (Fd3m) and rhombohedral (R3c) symmetry corresponding to ferrite and ferroelectric phase respectively. The 3-dimensional overview of crystal structure of pure CoFe₂O₄ and Na_0.5Bi_0.5TiO₃ and of composite 0.50CoFe₂O₄?0.50Na_0.5Bi_0.5TiO₃ is generated by using refined parameters. The dielectric constant (ε´) and dielectric loss (tanδ) values were recorded as a function of frequency ranging from 100?Hz to 7?MHz and at different temperatures. Both ε´ and tanδ follow dispersion pattern at lower frequencies while show frequency independent behavior at higher frequencies. The magnetic evaluation carried by analyzing M-H hysteresis loop reveals the ferrimagnetic characteristics of these composites. The highest value of magnetic moment is 1.12μ_B observed for composite 0.50CoFe₂O₄ – 0.50Na_0.5Bi_0.5TiO_3. Magnetoelectric (ME) voltage coefficient (α) was also demonstrated to observe the interaction between ferrite and ferroelectric phases. The highest value of α (72.72μV/Oe cm) is obtained for low ferrite composition 0.10CoFe₂O₄ – 0.90Na_0.5Bi_0.5TiO₃, which suggests the dependence of magnetoelectric response on the resistivity of the composites.     

Morphology and properties of nylon 6 and high density polyethylene blends in presence of nanoclay and PE‐g‐MA

In this study, we report the synergistic effect of nanoclay and maleic anhydride grafted polyethylene (PE‐g‐MA) on the morphology and properties of (80/20 w/w) nylon 6/high density polyethylene (HDPE) blend. Polymer blend nanocomposites containing nanoclay with and without compatibilizer (PE‐g‐MA) were prepared by melt mixing, and their morphologies and structures were examined with scanning electron microscopy (SEM) and wide angle X‐ray diffractometer (WAXD) study. The size of phase‐separated domains decreased considerably with increasing content of nanoclay and PE‐g‐MA. WAXD study and transmission electron microscopy (TEM) revealed the presence of exfoliated clay platelets in nylon 6 matrix, as well as, at the interface of the (80/20 w/w) nylon 6/HDPE blend–clay nanocomposites. Addition of PE‐g‐MA in the blend–clay nanocomposites enhanced the exfoliation of clays in nylon 6 matrix and especially at the interface. Thus, exfoliated clay platelets in nylon 6 matrix effectively restricted the coalescence of dispersed HDPE domains while PE‐g‐MA improved the adhesion between the phases at the interface. The use of compatibilizer and nanoclay in polymer blends may lead to a high performance material which combines the advantages of compatibilized polymer blends and the merits of polymer nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

NodeWiz: Fault-tolerant grid information service

Large scale grid computing systems may provide multitudinous services, from different providers, whose quality of service will vary. Moreover, services are deployed and undeployed in the grid with no central coordination. Thus, to find out the most suitable service to fulfill their needs, or to find the most suitable set of resources on which to deploy their services, grid users must resort to a Grid Information Service (GIS). This service allows users to submit rich queries that are normally composed of multiple attributes and range operations. The ability to efficiently execute complex searches in a scalable and reliable way is a key challenge for current GIS designs. Scalability issues are normally dealt with by using peer-to-peer technologies. However, the more reliable peer-to-peer approaches do not cater for rich queries in a natural way. On the other hand, approaches that can easily support these rich queries are less robust in the presence of failures. In this paper we present the design of NodeWiz, a GIS that allows multi-attribute range queries to be performed efficiently in a distributed manner, while maintaining load balance and resilience to failures.     

Color Subspaces as Photometric Invariants

Complex reflectance phenomena such as specular reflections confound many vision problems since they produce image ‘features’ that do not correspond directly to intrinsic surface properties such as shape and spectral reflectance. A common approach to mitigate these effects is to explore functions of an image that are invariant to these photometric events. In this paper we describe a class of such invariants that result from exploiting color information in images of dichromatic surfaces. These invariants are derived from illuminant-dependent ‘subspaces’ of RGB color space, and they enable the application of Lambertian-based vision techniques to a broad class of specular, non-Lambertian scenes. Using implementations of recent algorithms taken from the literature, we demonstrate the practical utility of these invariants for a wide variety of applications, including stereo, shape from shading, photometric stereo, material-based segmentation, and motion estimation.     

Estimation of relative evapotranspiration from NOAA PAL to derive growth characteristics in India

Clear‐sky dekadal relative evapotranspiration (RET) was derived using the surface energy‐balance approach applied to 10‐day composite NOAA PAL (8 km×8 km) datasets over the Indian landmass. This was further used to differentiate between growth characteristics for an irrigated intensive agriculture over a northern India state (e.g. Punjab) and a rainfed ill‐posed agriculture over a central India state (e.g. Madhya Pradesh) using time‐series data sets for five growing years (June–April): 1996–1997, 1997–1998, 1998–1999, 1999–2000, and 2000–2001. The triangular scatter between RET and normalized difference vegetation index (NDVI) showed that the minimum RET increases linearly with NDVI producing a ‘basal line’ that represents relative canopy transpiration only. A clear distinction in scatter was found between the two contrasting agro‐ecosystems showing a higher RET or root zone wetness in irrigated than rainfed systems. In rainfed rice‐growing regions, an inverse correlation (0.6–0.75) was found between RET and the Keetch–Byram meteorological drought index (KBDI), and a substantial reduction in RET was also found in a sub‐normal (2000) compared with a normal (1999) monsoon season. RET estimates were found to be most sensitive to atmospheric transmissivity followed by other land‐surface radiation budget inputs, such as NDVI, LST, and albedo. Error propagation due to three surface parameters is the opposite of that for transmissivity. The maximum possible error in clear‐sky NOAA PAL RET was estimated to be 12–15%. This test study would be helpful in deriving RET using optical and thermal data from a suite of current and future Indian geostationary satellite sensors for monitoring growing conditions.