Characterization of friction stir welded joint of low nickel austenitic stainless steel and modified ferritic stainless steel

Friction stir welding (FSW) of dissimilar stainless steels, low nickel austenitic stainless steel and 409M ferritic stainless steel, is experimentally investigated. Process responses during FSW and the microstructures of the resultant dissimilar joints are evaluated. Material flow in the stir zone is investigated in detail by elemental mapping. Elemental mapping of the dissimilar joints clearly indicates that the material flow pattern during FSW depends on the process parameter combination. Dynamic recrystallization and recovery are also observed in the dissimilar joints. Among the two different stainless steels selected in the present study, the ferritic stainless steels shows more severe dynamic recrystallization, resulting in a very fine microstructure, probably due to the higher stacking fault energy.     

Effect of Dynamic Change in Strain Rate on Mechanical and Stress Corrosion Cracking Behavior of a Mild Steel

The current work analyzes the effect of the dynamic change in strain rate during tensile loading of a mild steel on its mechanical and stress corrosion behavior in 3.5 wt.% NaCl solution. The sample experiences high strain rate (10^?2 s^?1) up to 10, 15 and 20% of total deformation and then very low strain rate of 10^?6 s^?1 till fracture without any unloading in between. The behavioral characteristics of the steel under these circumstances are found to be different from that exhibited during complete loading till fracture both at high and slow strain rates separately. Total strain increases with the increase in the strain at which change in strain rate happens, and this is attributed to the generation of large number of dislocations at higher strain rate and subsequently release of dislocation at low strain rate during change over due to more time available for dynamic recovery. This observation is common for both in air and corrosive environment. One unique observation in this study is the higher total strain and lower strength observed during dynamic change in strain rate in the corrosive environment compared to that in air, which is attributed to the hydrogen-induced plasticity mechanism.     

Effects of suction/blowing on steady boundary layer stagnation-point flow and heat transfer towards a shrinking sheet with thermal radiation

In this paper, the effects of suction/blowing and thermal radiation on steady boundary layer stagnation-point flow and heat transfer over a porous shrinking sheet are investigated. The existence of dual solutions, unique solution and non-existence of solution for self-similar equations of the flow and heat transfer are analyzed numerically. It is noted that the range of velocity ratio parameter where the solution exists increases/decreases with increasing suction/blowing. With increasing suction, temperature at the wall is found to increase (decrease) for the first (second) solution. Due to increasing Prandtl number and thermal radiation parameter the thermal boundary layer thickness becomes thinner.     

Analysis of a Localized Fire in a 3-D Tunnel Using a Hybrid Solver: Lattice Boltzmann Method,Finite-Volume Method,and Fully Explicit Upwind Scheme

A localized fire in a 3-D tunnel is analyzed by solving a combined-mode natural-convection and radiation problem. Nonlocal thermal equilibrium between air and smoke is considered. Separate energy equations are used for the two species. The density and temperature fields required for the solution of the energy equation are computed using the lattice Boltzmann method. The finite-volume method is used to compute radiative information. The energy equations are solved using the fully explicit upwind scheme. The Boussinesq approximation is used to account for the buoyancy effect. Effects of the scattering albedo, the convection-radiation parameter, and the wall emissivities on temperature profiles in the tunnel have been studied.     

Risk-Based Evaluation for Meeting Future Water Demand of the Brahmaputra Floodplain Within Bangladesh

A risk-based evaluation is performed for meeting future water demands in the Brahmaputra Floodplain Area within Bangladesh (BFA). This evaluation is carried out using three risk-based performance indicators: reliability, resiliency and vulnerability. The vulnerability indicator has been redefined incorporating the aspect of a supply failure. The analysis includes the impacts of climate change on both water demands and resources, and the generation of synthetic flows of the Brahmaputra River using time series models. The simulated values of the indicators reveal that the expected demand of the BFA up to the year 2050 can be supplied with the proposed Brahmaputra Barrage inside Bangladesh under the ‘no change’ in climatic condition, provided that the groundwater remains usable. However, if groundwater becomes unusable due to widespread arsenic contamination and/or a climate change occurs, it would not be possible to meet the future water demand of the region with high reliability, moderate resiliency and low vulnerability.     

Iron-Doped,Mullite-Impregnated PVDF Composite: An Alternative Separator for a High Charge Storage Ceramic Capacitor

In this communication, the formation mechanism of the electroactive β phase, morphology and the dielectric activities of increasing doping concentration (0–1.2 M.W % of mullite) of Fe²⁺ ion-doped, mullite-impregnated polyvinylidene fluoride (PVDF) nanocomposite have been investigated. Differential thermal analysis (DTA) confirms the formation of an electroactive β phase, and Fourier transform infrared spectroscopy (FTIR) showed that the β phase increases simultaneously and attains the maximum increment of 2.6 times compared to pristine PVDF. X-ray diffraction (XRD) spectra also agreed well with the β-phase increment behaviour and also confirmed the presence of required mullite phases. Field emission scanning electron microscopy (FESEM) images indicate the strong interaction between the polymer matrix and different concentrations of Fe²⁺ ion-doped mullite particles, resulting in enhanced electroactive β phase formation and large dielectric constant of the nanocomposite films followed by significant low dielectric loss with high ac conductivity compared to pristine PVDF films at room temperature. This doped polymer composite can be used as a high dielectric separator and, using this separator, we have successfully fabricated a high-charge-storage device. This paper also demonstrates that the loading of conductive Fe²⁺ ions within the highly insulating mullite matrix has a critical concentration for the enhancement and nucleation of the electroactive β phase of the PVDF polymer. In this critical concentration, the highest formation of a β network and maximum numbers of homogeneously distributed iron-doped mullite (FeM) particles in PVDF matrix improves the effective interfacial polarization by Maxwell–Wagner–Sillar (MWS) polarization effect which is responsible for the enhancement of dielectric constant and ac conductivity followed by significant tangent loss. So, it can be concluded that the incorporation of Fe²⁺-doped mullite into PVDF matrix is an effective way to fabricate a high dielectric separator of high-charge-storage electronic devices.     

Catalyst development for thermocatalytic decomposition of methane to hydrogen

The paper presents the results of the investigation into the development of a robust catalyst for hydrogen production by thermocatalytic decomposition (TCD) of methane. In this paper, we present the results of the development and utilization of an iron-based catalyst for TCD. The effect of catalyst preparation methodology on the activity and robustness of the catalysts is reported. The catalyst was synthesized from magnetite by reduction in the presence of a reducing gas (methane or hydrogen) using a fixed-bed flow reactor at atmospheric pressures and temperatures ranging from 800 to 900 °C. Reduction under methane was found to synthesize a catalyst with the desired properties and smallest preparation time (2 h). The main advantages of these catalysts identified were: their ability to completely decompose methane (as compared to a maximum of 81% by other catalysts) and to maintain high reactivity for a long period of time (more than 75 h). The catalyst was characterized by SEM, TEM, BET, XRD and particle size analysis. TPR was employed to evaluate the activity of the catalysts, to investigate the various mechanisms of methane decomposition reaction for the catalysts and estimate the kinetic parameters by topochemical model postulated by Avrami–Erofeyev. The estimated kinetic parameters from the analysis of this data are presented. Carbon nanofibers were formed as a co-product of the methane decomposition reactions.     

A production-recycling-inventory model with learning effect

This paper develops an integrated production-recycling system over a finite time horizon. Here, the dynamic demand is satisfied by production and recycling. The used units are bought back and then either recycled or disposed of which are not repairable. The used units are collected continuously from the customers. Recycling products can be used as new products which are sold again. The rate of production and disposal are assumed to be function of time. The setup cost is reduced over time due to “Learning curve” effect. The optimum results are presented both in tabular form and graphically.     

Tannase production by Bacillus licheniformis KBR6: Optimization of submerged culture conditions by Taguchi DOE methodology

Tannase production by Bacillus licheniformis KBR6 under submerged fermentation was optimized following Taguchi orthogonal array (OA) design of experiment (DOE). An OA layout of L18 (2¹ × 3⁵) was constructed with six most influensive factors on tannase biosynthesis like, carbon source (tannic acid), phosphate source (KH₂PO₄), nitrogen source (NH₄Cl), metal ion (Mg²⁺), incubation temperature and initial medium pH at three levels for the proposed experimental design. Tannase yield obtained from the 18 batches fermentation with the selected levels of each factors were processed with Qualitek-4 software at bigger is better as quality character and obtained a specific combination of factors with a predicted tannase production of 0.362 U/ml. The optimal combinations of factors (tannic acid, 1.0 g%; KH₂PO₄, 0.45 g%; NH₄Cl, 0.35 g%; MgSO₄, 0.05 g%) obtained from the proposed DOE methodology was further validated by fermentation experiment and the obtained result revealed an enhanced tannase yield of 2.18-fold (from 0.163 U/ml to 0.356 U/ml) from its unoptimized condition. Taguchi approach of DOE resulted in evaluating the main and interaction effects of the factors individually and in combination.     

In situ nanocrystalline Fe–Si coating by mechanical alloying

A new approach for deposition of in situ nanocrystalline Fe–Si alloy coating on mild steel substrate by mechanical milling has been proposed. The thickness of nanocrystalline coating was a function of milling time and speed. Milling speed of 200 rpm was the optimum condition for development of uniform, hard, adherent and dense 200–300 μm thick nanocrystalline coating. A possible mechanism, consisting of three steps like repeated impact, cold welding and delamination, has been proposed for the formation of coating. These coatings have resulted in the increase of the hardness to almost double the value before coating.