Experimental Investigations on Microstructure,Properties and Workability Behavior of Zinc Oxide Reinforced Al–Si–Mg Matrix Composites

Silicon - Al-Si based alloy matrix composites are now broadly utilized by the industrial sectors like automobile, structural, aerospace and more practical industrial applications due to its...     

An analytical solution to wellbore stability using Mogi-Coulomb failure criterion

Deep wellbores/boreholes are generally drilled into rocks for oil and gas exploration, monitoring of tectonic stresses purposes. Wellbore and tunnel in depth are generally in true triaxial stress state, even if the ground is under axisymmetric loading condition. Stability of such wellbores is very critical and collapse of wellbore must be avoided. Mogi-Coulomb failure criterion is a better representation of rock strength under true triaxial condition. In this paper, an analytical solution is proposed using Mogi-Coulomb failure criterion. The solution is obtained for rock mass exhibiting elastic-perfectly plastic or elastic-brittle-plastic behaviour considering in-plane isotropic stresses. The proposed solution is then compared with exact analytical solution for incompressible material and experimental results of thick-wall cylinder. It is shown that the results obtained by the proposed analytical solution are in good agreement with the experimental results and exact analytical solution. A reduction of about 13%–20% in plastic zone from the proposed closed-form solution is observed, as compared to the results from the finite element method (FEM) based Mohr-Coulomb criterion. Next, the influences of various parameters such as Poisson's ratio, internal pressure (mud weight), dilation angle, and out-of-plane stress are studied in terms of stress and deformation responses of wellbore. The results of the parametric study reveal that variation in the out-of-plane stress has an inverse relation with the radius of plastic zone. Poisson's ratio does not have an appreciable influence on the tangential stress, radial stress and radial deformation. Dilation angle has a direct relation with the deformation. Internal pressure is found to have an inverse relation with the radial deformation and the radius of plastic zone.     

Chitosan Schiff base as effective corrosion inhibitor for mild steel in acid medium

An environment friendly inhibitor, chitosan thiophene carboxaldehyde Schiff base, was synthesized by a condensation reaction of the carbonyl group of thiophene 2‐carboxaldehyde and free amino groups of chitosan. The chitosan Schiff base was characterized by UV spectroscopy, Fourier transform IR spectroscopy, elemental analysis and thermal analysis. The surface morphology of the Schiff base derivative was examined by SEM. Gravimetric and electrochemical techniques were used to explore the behaviour of the chitosan thiophene derivative as a corrosion inhibitor for mild steel in an acidic environment. The effects of inhibitor concentration, exposure time and temperature were investigated. The chitosan Schiff base showed a good inhibition performance of 92% inhibition efficiency at room temperature for 12 h of immersion in a weight loss experiment. The electrochemical results showed that the chitosan derivative acts as an effective mixed type inhibitor. The adsorption of the inhibitor followed the Temkin isotherm model. SEM and AFM techniques were used to characterize the protective layer formed on the mild steel substrate. © 2016 Society of Chemical Industry     

Modeling and analysis of rapid catalyst aging cycles

The primary mode of deactivation of automotive emission control catalysts is thermal aging, and it is well-known that high-temperature lean aging conditions are particularly detrimental. Since evaluating the long-term durability of automotive catalysts is costly and time-consuming, rapid catalyst aging cycles have been developed to mimic (in a reduced time) the catalyst deactivation under real-world driving conditions. One of the commonly used rapid catalyst aging tests is an exothermal aging cycle, which involves a combination of fuel-rich engine operation and supplemental air injection to generate high-temperature lean conditions within the catalyst bed. In this work, we use the previously developed transient three-way catalyst model to investigate the time evolution of the axial temperature profiles and exhaust air–fuel ratio (A/F) along the catalyst bed during the course of the exothermal rapid aging cycles. We find that the thermal front propagates downstream through the catalyst bed relatively slowly (compared to the concentration front) and this can limit the location within the catalyst bed and duration for high-temperature lean exposure. We also investigate how variations of some of the key system design and operating parameters can affect the extent and duration of high-temperature lean exposure. Finally, a simple analytical expression is developed which allows one to estimate the time it takes for the thermal front to travel through the catalyst bed. This time can be compared with the period of the lean A/F operation during the aging cycle to determine the location and duration of high-temperature lean exposure.     

Effects of postmortem storage time on color and mitochondria in beef

To assess the effects of aging time (0, 15, 30, and 45 d) and temperature (0 or 5 °C) on beef mitochondria and steak color, vacuum packaged longissimus (n = 15) and cardiac muscles were assigned to 1 of 6 temperature × time combinations. As time increased, initial red color intensity increased whereas both mitochondrial oxygen consumption and color stability decreased. The decrease in mitochondrial oxygen consumption associated with longer aging times will increase initial color intensity. However, this improvement in color development will be negated by the decreased color stability that results from the effects of storage on mitochondria.     

A support vector regression approach to detection in large-MIMO systems

We propose a support vector regression approach for symbol detection in large-MIMO systems employing spatial multiplexing. We explore the applicability of machine learning algorithms, in particular support vector machines, to address one of the recent research problem in communications.The machine learning capability is exploited to achieve fast detection in large dimension systems. The performance of the proposed method is compared with lattice reduction aided detection which is currently the popular choice and the improvement in terms of bit error rate is demonstrated. The sparse formulation of the problem matrix reduces the computational complexity and enables faster detection. The proposed detection algorithm is tailored to address both uncorrelated and correlated channel conditions as well.     

Experimental and theoretical investigation on microwave melting of metals

Experiments were conducted for microwave heating and melting of lead, tin, aluminium and copper with the aid of susceptors and the detailed results were presented for various microwave power levels and sample loading. Aluminium and copper samples were heated in presence of inert gas to minimize oxidation. Compared to conventional melting, microwave melting was twice as fast and more energy efficient. Lumped parameter model of the heating process showed that the conversion of microwave to thermal energy was enhanced at higher temperatures, justifying this a favourable process for metal melting applications.     

Hot deformation behaviour of 7075 alloy

The hot deformation behaviour of Stir cast 7075 alloy was studied using processing map technique. The map has been interpreted in terms of the microstructural processes occurring in situ with deformation, based on the values of a dimensionless parameter η which is an efficiency index of energy dissipation through microstructural processes. An instability criterion has also been applied to demarcate the flow instability regions in the processing map using another parameter (ξ). Both the parameters (η and ξ) were computed from the experimental data generated by compression tests conducted at various temperatures and strain rate combinations over the hot working range (300-500 °C and 0.001-1.0 s⁻¹) of the present material. The processing map exhibits one distinct η domains without any unstable flow conditions under the investigated temperature and strain rate conditions. The dynamic recrystallization zone and instable zones, i.e. adiabatic shear band formation, interface crack, and wedge cracking, were identified in the processing map. Microstructural examination was performed for validation. The processing maps can be used to select optimum strain rates and temperatures for effective hot deformation of 7075 alloy.