Numerical simulation of tensile strength of upset welded joints with experimental verification

Resistance upset welding (UW) is a widely used process for joining metal parts. In this process current, time and upsetting force are three parameters that affect the quality of welded products. This paper considers numerical simulation and experimental investigation of UW process parameters. The investigated parameters include heating and post-weld heating current and their corresponding duration as well as interference of the part features that form the joint. In this study, evaluation of tensile strength of the welded joint with variation of the process parameters is also reported. For numerical analysis, a two-dimensional axisymmetric model using a coupled electro-thermal finite element method is developed to study the thermal behavior of the welded joints. The results of this numerical simulation are used to determine the status of the weldment and therefore evaluate the quality of the weld at the joint. Both numerical and experimental results suggest an optimum set of welding parameters, i.e. time and electrical current that yields a maximum value for the tensile strength of the joint. Also the effects of post-weld heating time and current on the tensile strength are evaluated and show that these parameters have a remarkable effect on improving tensile strength of the weldment.     

Interpretation of Cyclic Potentiodynamic Polarization Test Results for Study of Corrosion Behavior of Metals: A Review

Protection of Metals and Physical Chemistry of Surfaces - The cyclic potentiodynamic polarization technique is a method for evaluating the susceptibility of a metal to localized corrosion such as...     

Optimum design of structures with stress and displacement constraints using the force method

A new structural analysis and optimization algorithm is developed to determine the minimum weight of structures with the truss and beam-type members under displacement and stress constraints. The algorithm combines the mathematical programming based on the sequential quadratic programming (SQP) technique and the finite element technique based on the integrated force method. The equilibrium matrix is generated automatically through the finite element analysis while the compatibility matrix is obtained directly using the displacement–deformation relations and the single value decomposition (SVD) technique. By combining the equilibrium and compatibility matrices with the force–displacement relations, the equations of equilibrium with the element forces as variables are obtained. The proposed method is extremely efficient to analyze and optimize the truss and beam structures under stress and displacement constraints. The computational effort required by the force method is found to be significantly lower than that of the displacement method. The effect of the geometric nonlinearity in the structural optimization problems under the stress and displacement constraints were also investigated and it is illustrated that the geometric nonlinearity is not an important issue in these types of problems and hence, it does not affect the final optimum solution significantly. Four examples illustrate the procedure and allow the results to be compared with those reported in the literatures.     

Path diversity for FFH/PSK spread-spectrum communication systems

A fast frequency hopping (FFH) method which uses path-diversity combining is proposed. Diversity techniques are realized when a signal is received from diverse independent paths, each of which carries identical information but suffers from independent fading variations. The improvement of communication performance of FFH systems is possible as the delayed paths are used and path-diversity combination is realized. The advantages of this method, operating in Rayleigh fading channels are confirmed by theoretical analyses. The improvement is in order of 2~3 dB at bit error rate (BER) of 10^-3. This method can be also effective against interferences from other users in a code division multiple access (CDMA) environment. The performance of this system in a CDMA environment is evaluated by theoretical analyses and is shown to be superior to non-combining method. At BER of 10^-3 the required E_b/N₀ of the proposed system is 5 dB lower. If E_b/N_o is fixed, a greater number of users can be accommodated using the proposed system     

Optimization and characterization of pulse electrodeposited nickel selenide nanostructure as a bifunctional electrocatalyst by response surface methodology

The electrocatalytic activity of the pulse electrodeposited Ni–Se coating on nickel foam (NF) for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) was optimized by design of experiments. In this study as the first step of optimization, the condition of electrodeposition bath containing the ratio of Se/Ni, pH, and temperature was optimized. The response surface methodology (RSM) in central composite design (CCD) was used for experiments based on the parameters of the ratio of Se/Ni and pH. The prediction model after carrying out the analyses of variance (ANOVA) on the responses showed the best desirable values for the ratio of Se/Ni and pH were 0.7 and 3.6. The nanostructure Ni–Se electrode electrodeposited in the optimal condition requires 103 and 249 mV (vs. RHE) for delivering 10 mA/cm² in HER and OER, respectively. To temperature survey, the optimized Ni–Se electrode was synthesized at 25, 40, and 60 °C. Results showed that the electrode electrodeposited at the ambient temperature with large electrochemically active surface area of 8960 and low Tafel slopes of 86 and 35 mV/dec has the superior electrocatalytic performance for HER and OER, respectively.     

Conformable displays based on polymer‐dispersed liquid‐crystal materials on flexible substrates

Abstract— We have developed a process that enables one to conform polymer‐dispersed liquid‐crystal (PDLC) displays into a particular shape indefinitely. Planar PDLC displays are first fabricated between indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates. This fully functional display can then be conformed to a particular shape by heating above the glass‐transition temperature of PET and then allowing it to cool down to room temperature. The display retains its shape and is fully functional after processing. We have created spiral‐and wave‐like samples and have demonstrated their operation after the conformal process. The stress is relieved in the substrate by conforming. Temperature effects on polymer substrates were investigated for two types of polymer films (PET/ITO substrates and a conducting polymer PEDOT:PSS/PET substrate) to analyze the effects of temperature on the resistance and mechanics of the films under an applied uniaxial strain. We have found a decrease in contrast of the PDLC after conforming, but surprisingly, a reduced threshold voltage and reduced hysterisis occurs.     

Design of a VDC System for All-Wheel Independent Drive Vehicles

It is shown that the vehicle dynamic control (VDC) system can improve the vehicle handling and active safety of driver and passengers considerably. The control of vehicle yaw moment through differential braking, based on the vehicle dynamic state feedbacks, is a traditional way of VDC. In this study, a new VDC system for a four motorized-wheels electric vehicle has been developed, for which the traction of each wheel can be controlled individually. Using this feature, the new VDC system provides the desired tractive force of vehicle and the desired external yaw moment through the integrated control of wheel motors. The structure of the control system is a multilayer type, which has been developed by using independent controllers, designed in accordance with the appropriate theories.     

PKM capabilities and applications exploration in a collaborative virtual environment

This paper introduces an integrated validation system that consists of the following modular components: kinematic/dynamic analysis module, kinetostatic model, CAD module, FEM module, CAM module, optimization module and virtual environment for remote control. In this paper, authors focus mainly on the modules of kinetostatic modeling, dynamic modeling, PKM design optimization and remote control realization. The prototype of a 3-dof Parallel Kinematic Machine (PKM) developed at the Integrated Manufacturing Technologies Institute of National Research Council of Canada (NRC-IMTI) is used as an example throughout this paper.     

Modeling and performance analysis of duck‐shaped triboelectric and electromagnetic generators for water wave energy harvesting

Triboelectric nanogenerator (TENG) is a newly proposed technology for effectively converting mechanical energy into electricity. Triboelectric nanogenerator has shown a great potential for harvesting the clean and abundant energy of ocean waves. Recently, a duck‐shaped TENG device has been proposed as a lightweight, cost‐effective, highly stable, and efficient system for scavenging the existing energy in water waves. In this paper, a detailed investigation on the performance of the duck‐shaped TENG is presented. Then, a comparative analysis between the TENG device and an equivalent electromagnetic generator (EMG) for wave energy harvesting is performed. The electric output characteristics of both techniques under various mechanical and electrical conditions are obtained. The analysis demonstrates that at a low operating frequency of 2.5 Hz, the TENG and EMG achieve the peak power density of 213.1 and 144.4 W/m³, respectively. The present paper provides guidance for design and optimization of hybrid TENG and EMG technology toward scavenging the blue energy.