Predicting tensile strength,hardness and corrosion rate of friction stir welded AA6061-T6 aluminium alloy joints

AA6061-T₆ aluminium alloy (Al–Mg–Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to-weight ratio and good corrosion resistance. The friction stir welding (FSW) process and tool parameters play major role in deciding the joint characteristics. In this research, the tensile strength and hardness along with the corrosion rate of friction-stir-butt welded joints of AA6061-T₆ aluminium alloy were investigated. The relationships between the FSW parameters (rotational speed, welding speed, axial force, shoulder diameter, pin diameter and tool hardness) and the responses (tensile strength, hardness and corrosion rate) were established. The optimal welding conditions to maximize the tensile strength and minimize the corrosion rate were identified and reported here.     

Mesoscale Modeling and Validation of Texture Evolution during Asymmetric Rolling and Static Recrystallization of Magnesium Alloy AZ31B

The focus of the present research is to develop an integrated deformation and recrystallization model for magnesium alloys at the microstructural length scale. It is known that in magnesium alloys nucleation of recrystallized grains occurs at various microstructural inhomogeneities such as twins and localized deformation bands. However, models need to be developed that can predict the evolution of the grain structure and texture developed during recrystallization and grain growth, especially when the deformation process follows a complicated deformation path such as in asymmetric rolling. The deformation model is based on a crystal plasticity approach implemented at the length scale of the microstructure that includes deformation mechanisms based on dislocation slip and twinning. The recrystallization simulation is based on a Monte Carlo technique that operates on the output of the deformation simulations. The nucleation criterion during recrystallization is based on the local stored energy, and the Monte Carlo technique is used to simulate the growth of the nuclei resulting from local stored energy differences and curvature. The model predictions are compared with experimental data obtained through electron backscatter analysis and neutron diffraction.     

Implementation and use of the PLT scheme Web server

The PLT Scheme Web Server uses continuations to enable a natural, console-like program development style. We describe the implementation of the server and its use in the development of an application for managing conference paper reviews. In the process of developing this application, we encountered subtle forms of interaction not directly addressed by using continuations. We discuss these subtleties and offer solutions that have been successfully deployed in our application. Finally, we present some details on the server’s performance, which is comparable to that of the widely-used Apache Web server. This research is partially supported by multiple NSF grants. Preliminary versions of parts of this material have appeared in print (Lecture Notes in Computer Science, vol. 2638, pp. 100–128, 2003; European Symposium on Programming, pp. 122–136, 2001; Scheme Workshop, pp. 53–58, 2003; Symposium on the Practical Aspects of Declarative Languages, pp. 2–16, 2003). P.W. Hopkins’ current affiliation: Google, Inc. P.T. Graunke’s current affiliation: Galois Connections, Inc. G. Pettyjohn’s current affiliation: Turbine, Inc.     

Failure analysis of an ammonia refrigerant condenser tube

A detailed failure analysis was conducted on an ammonia refrigerant condenser tube component that failed catastrophically during its initial hours of operation. Evidence collected clearly demonstrated that the weld between a pipe and a dished end contained a sharp unfused region at its root (lack of penetration). Component failure had started from this weld defect. The hydrogen absorbed during welding facilitated crack initiation from this weld defect during storage of the component after welding. Poor weld toughness at the low operating temperature facilitated crack growth during startup, culminating in catastrophic failure as soon as the crack exceeded critical length.     

Aldimines — Effective Corrosion Inhibitors for Mild Steel in Hydrochloric Acid Solution

New and effective aldimine types of corrosion inhibitors namely, N-methylidene octylamine (MOA), N-ethylidene octylamine (EOA) and N-propylidene octylamine (POA) have been synthesized. Their inhibition efficiency was investigated for the corrosion of mild steel in 1 M HCl solution by various corrosion monitoring techniques. A preliminary screening of the inhibition efficiency of the inhibitors was carried out by weight loss and gasometric studies. They were found to behave as good inhibitors in 1 M HCl solution. Potentiodynamic polarization measurements show that aldimines are mixed type inhibitors. The extent of the decrease in the hydrogen permeation current through the mild steel surface was studied by the hydrogen permeation technique and it was found that the decrease was in the order POA > EOA > MOA. Double layer capacitance and charge transfer resistance values were derived from Nyquist plots obtained from AC impedance studies. The adsorption of these compounds on mild steel from 1 M HCl solution obeys the Temkin adsorption isotherm.     

A Comprehensive Neural Network Model for Colorization and Captioning of Images Along with IoT Deployment

The convergence of artificial neural networks and the internet of things (IoT) has gained popularity in the field of computer science research. In this work, an efficient neural network model for the image colorization problem is proposed along with deploying these models to the remote system using IoT deployment tools. Further, this work proposed two convolution neural network models namely the Alpha model and Beta model towards solving the image colorization of the grayscale format. An efficient combination of models is proposed and analyzed such that the loss rate is minimized as?~?0.005. Next, an efficient model for solving image captioning is proposed based on the bi-directional long short term memory model. Finally, the work discusses the merits and demerits of deploying the neural network model using the AWS Greengrass and Docker IoT environment on remote systems.

     

Microstructure and Sn Crystal Orientation Evolution in Sn-3.5Ag Lead-Free Solders in High-Temperature Packaging Applications

Understanding the reliability of eutectic Sn-3.5Ag lead-free solders in high-temperature packaging applications is of significant interest in power electronics for the next-generation electric grid. Large-area (2.5 mm × 2.5 mm) Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates were thermally cycled between 5°C and 200°C. Sn crystal orientation and microstructure evolution during thermal cycling were characterized by electron backscatter diffraction in the scanning electron microscope. Comparisons were made between the observed initial texture and microstructure and its evolution during thermal cycling. Gradual lattice rotation and grain boundary misorientation evolution observed due to thermal cycling suggested a continuous recrystallization mechanism. Recrystallization behavior was correlated with dislocation slip activities.     

Processing of titanium-based human implant material using wire EDM

Machinability of human implant materials without causing any surface damage is a challenge on current research. The effect of heat-affected zone (HAZ), load experienced, and chemical reaction after implantation are the profound factors influencing on degradation of implant machined surface. An attempt is made to study the machinability of titanium-based human implant materials. While machining, the surface quality of the implant materials with reference to electrochemistry and metallurgical behavior of plasma energy produced are investigated in detail. Materials removal and its surface quality during plasma spark were measured as a response on machining process. The influence of pulse on/off time and the voltage varied during experimentation are evaluated using factorial design. Further, the machined samples are subjected to metallurgical characterization studies using microscopic (SEM) and spectroscopic (EDS) analysis. Increase in voltage has produced better surface finish and reduced recast layer. Contribution of pulse duration is less compared to voltage. Thus, the difficulty on machining human implants can be performed with wire electrical discharge machining process with high surface quality.     

Fermi-edge singularity in photoluminescence spectra of modulation-doped AlGaAs/InGaAs/GaAs quantum wells

The photoluminescence study of Fermi-edge singularity (FES) in modulation-doped pseudomorphic Al _x Ga_1?x As/In _y Ga_1?y As/GaAs quantum well (QW) heterostructures is presented. In the above QW structures the optical transitions between n = 1 and n = 2 electronic subband to the n = 1 heavy hole subband (E ₁₁ and E ₂₁ transitions, respectively) are observed with FES appearing as a lower energy shoulder to the E ₂₁ transition. The observed FES is attributed to the Fermi wave vector in the first electronic subband under the conditions of population of the second electronic subband. The FES appears at about 10 meV below E ₂₁ transition around 4·2 K. Initially it gets stronger with increasing temperature and becomes a distinct peak at about 20 K. Further increase in temperature quenches FES and reaches the base line at around 40 K.     

Characterization of zinc-nickel alloy electrodeposits obtained from sulphamate bath containing substituted aldehydes

Zinc alloy offers superior sacrificial protection to steel as the alloy dissolves more slowly than pure zinc. The degree of protection and the rate of dissolution depend on the alloying metal and its composition. Zinc-nickel alloy may also serve as at less toxic substitute for cadmium. In this paper the physico-chemical characterization of zinc-nickel electrodeposits obtained from sulphamate bath containing substituted aldehydes was carried out using hardness testing, X-ray diffraction, and corrosion resistance measurements. The corrosion behaviour of these samples in a 3.5% NaCl solution was examined. The decrease inI _corr and high charge transfer resistance indicated the improved corrosion resistance of these deposits.