Study on Optimization of Parameters Affecting Simple Shear Extrusion of Pure Copper to Fabricate Fine Grain Structure

During last decades, severe plastic deformation (SPD) techniques have developed and increased their applications in variety of industries such as aerospace, nuclear, automotive, marine etc. One of emerging SPD process is simple shear extrusion (SSE). In the present study, an attempt was made to optimize parameters affecting SSE process of pure copper namely maximum distortion angle, channel length and ram speed on effective plastic strain and maximum punch force. Firstly, the process was numerically simulated by use of ABAQUS software. Then, the developed finite element model was verified by confirmatory experiment taking into account the punch force. 15 series of simulation runs were implemented incorporating three aforementioned factors within three levels. Then, response surface methodology was used here to correlate relationship between process parameters to forming force and effective strains. Sensitivity analysis was also carried out to find which factor had greatest impact on process quality characteristics. In order to find optimal parameter setting for maximum strain and strain rate as well as minimum punch force, desirability approach was utilized. Results revealed that distortion angle was the most significant factors affecting plastic strain and punch force, while the ram speed had greatest impact on strain rate. The specimens at optimum parameters (i.e. 45° distortion angle, 90 mm channel length and 0.3 mm/s ram speed that resulted in maximum plastic strain) were processed by SSE and mechanical properties and microstructure analysis were studied. It was found from the results that microstructure of the samples were significantly refined by performing SSE at optimum level that resulted in improvement of samples strength and hardness.     

ESIV: an end-to-end secure internet voting system

Nowadays, with the growing popularity of e-Government services, security of client platforms and violation of citizen e-rights are of great concerns. Since Internet-voting protocols have no control over voter-side platforms, bribery/coercion and breaching vote’s privacy and voter’s anonymity are feasible. In fact, the voter-side platform (voter’s PC) is easily vulnerable to malicious software (cyber-attacks) and can totally breach security of the entire voting protocol. We have proposed ESIV: an end-to-end secure internet-voting system that highly guarantees: voter and server-side platform’s security, verifiability, fairness, resistance to bribery/coercion and voting authorities collusion besides simultaneous election support while preserving eligibility, anonymity, privacy and trust. In addition, we utilize Java Card 3 technology as an independent secure web-server which is connected directly to network in order to send/receive HTTP(S) requests using high-speed interfaces. This technology brings about independence from utilizing any trusted device at voter-side and provides end-to-end security. Finally, an implementation of ESIV is presented and ESIV security features are evaluated.     

Numerical Study of the Effects of Drainage Systems on Saturated/Unsaturated Seepage and Stability of Tailings Dams

The stability of tailings dams is affected by seepage characteristics such as the location of the phreatic surface inside the dam, the effects of the capillary fringe, and the unsaturated zone above the zero pore pressure level. In this study, the performance of drainage systems in tailings dams was investigated by analyzing saturated and unsaturated seepage in the dam, considering the effects of the construction method, tailings properties, and the type of drainage systems. First, general seepage characteristics in tailings dams were studied and the effects of non-homogeneity were investigated. Our results show that in a silty tailings dam with a height of 15 m, unsaturated plus capillary seepage flux can reach 13% of the total seepage. The total head vs. discharge volume curves under various conditions were compared and their practical implications are presented. Then, stability analyses were carried out using the results of seepage analyses for different construction methods, material properties, and drainage systems. Finally, a number of practical conclusions are drawn regarding dam stability and the efficiency of toe, blanket, and chimney drains in different construction methods. Using a blanket and/or a chimney drain can increase the stability safety factor by up to two times, depending on the type of material.     

An integrated fault estimation and fault tolerant control method using H∞-based adaptive observers

An integrated fault estimation/fault-tolerant control (FTC) scheme is developed in this article for nonlinear Lipschitz systems in the presence of external disturbances and actuator failures. To address this problem, coupled uncertainties between the observer error dynamics and the control system are considered, which is conveniently ignored in control approaches based on the separation principle. An H_∞ -based adaptive observer is proposed to simultaneously estimate the system states and actuator faults without the restrictive strictly positive realness or persistent excitation conditions. The FTC is constructed by sliding mode control using the estimated states generated by the developed observer. A novel sufficient condition is derived in terms of linear matrix inequality (LMI) including both the system control dynamics and the estimation errors; then, the control parameters and observer gains are simultaneously obtained via solving the mentioned LMI based on the H_∞ optimization. Finally, a flexible joint robot is considered to illustrate the effectiveness of the developed method.     

Silica chemically bonded N-propyl kriptofix 21 and 22 with immobilized palladium nanoparticles for solid phase extraction and preconcentration of some metal ions

Silica gel chemically bonded N-propyl kriptofix 21 (SBNPK 21) and N-propyl kriptofix 22 (SBNPK 22) and subsequently immobilized with palladium nanoparticles (PNP-SBNPK 21 and PNP-SBNPK 22) to produce two new complexing lipophilic materials. Then these novel sorbents were applied for the enrichment of some metal ions and their subsequent determination by flame atomic absorption spectroscopy (FAAS). The influences of the variables including pH, amount of solid phase, sample flow rate, eluent conditions and sample volume on the metal ion recoveries were investigated. The detection limit of proposed method was in the interval 2.1–2.3 and 1.7–2.8 ng mL^? 1 for PNP-SBNPK 21 and PNP-SBNPK 22 respectively, while the preconcentration factor was 80 for two sorbents. The relative standard deviations of recoveries were between 1.23–1.31 and 1.28–1.49 for PNP-SBNPK 21 and PNP-SBNPK 22 respectively. The method has high sorption-preconcentration efficiency even in the presence of various interfering ions. Due to the reasonable selectivity of proposed method, the relative standard deviation of recoveries of all understudied metal ions in some complicated matrices was less than 3.0%.     

Dissimilar Friction-Stir Lap Joining of 5083 Aluminum Alloy to CuZn34 Brass

In this research, lap joining of Al-Mg aluminum alloy and CuZn34 brass was produced by friction-stir welding during which the aluminum alloy sheet was placed on the CuZn34. Optical microscopy, scanning electron microscopy (SEM), X-ray diffraction analysis, and energy-dispersive X-ray spectroscopy (EDS) analysis were used to probe the microstructures and chemical compositions. In addition, the mechanical properties of each sample are characterized using both shear and hardness tests. The optimum parameters resulted in no visible welding cracks and defects. A dark area in the Al/CuZn34 interface contained intermetallic compounds Al₂Cu, Al₄Cu₉, and CuZn. In addition, the results show that using high rotational speeds or low traverse speeds causes the growth of the interfacial intermetallic area.