Modares Mechanical Engineering
Year:2019 | Volume:19 | Issue:2 |Papers Count:27

Nonlinear behavior of an initially curved fully clamped microbeam is investigated in this paper. The microbeam is laminated between two thin piezoelectric layers along its length. Applying voltage to the piezoelectric layers induces a lengthwise force in the microbeam which, in turn, changes the initial rise and the bending stiffness of the microbeam. This feature is used to tune the frequency and the bistability band of the initially curved microbeam for the first time in this paper. The microbeam is electrostatically actuated as well. The governing equation of motion is obtained, using the Hamilton’ s principle and the size effect is considered in the formulation of the problem utilizing the strain gradient theory. Static response of the system is obtained, using the Newton-Raphson numerical approach. The natural frequency of the system is obtained for various electrostatic voltages. The influence of piezoelectric actuation and size effect is studied on the static behavior and the frequency of the microbeam. Dynamic response of the microbeam in the vicinity of the primary resonance is obtained, using shooting technique and in some cases by the method of multiple scales. The effect of size and piezoelectric excitation on the primary resonance is investigated. The secondary resonance of the microbeam subjected to subharmonic resonance of order 1/2 and the influence of size on it is also studied.

Incremental sheet forming is one of the novel processes, which is used for rapid prototyping and manufacturing of parts with complex geometries. Forming limit of sheet metal in this process is high compared to other conventional forming processes. In this paper, warm singlepoint incremental forming process through uniform heating to sheet along with tool heating is studied experimentally and numerically. Formability of sheet is investigated in various process condition based on the straight groove test in experimental approach and numerical simulation, using finite element method. Tool heating along with uniform heating to sheet makes tool and sheet isothermal, reduces the heat loss in deformation zone, and improves the deformation process. So, attainment of high forming limit is made possible. Comparison of forming limit diagrams obtained from experimental and numerical approaches shows a good agreement between the results. Effects of temperature and feed rate on the forming limit of aluminum 1050 sheet are investigated. Results show that increasing the temperature improves the formability of sheet significantly; but, the temperature is more influential on forming limit in low feed rates. Increasing the feed rate reduces the forming limit slightly; this effect is more evident in higher temperatures.

The Constrained Groove Pressing (CGP) process is one of the most effective and newest methods of the severe plastic deformation for production ultrafine-grain metal sheets. In this research, the effect of CGP on the microstructure and mechanical properties of pure copper sheets was investigated. In order to study the microstructure of the samples, the optical microscopy was used, and tensile and Vickers micro-hardness tests were utilized for the evaluation of the mechanical properties. Investigating the microstructure of CGPed sheets determined that the CGP process has caused intense grain refinement, especially at first pass. Also, the results of mechanical properties showed that this process has considerably increased strength and hardness of the copper samples. In the numerical investigation of constrained groove pressing, effective strain and forming force were evaluated, using finite element simulation and the results indicated that with increasing number of CGP passes, effective strain, and forming force increase. Also, distribution of effective strain illustrated that the center of samples are under more effective strain that causes increasing hardness inside the samples be more than increasing hardness of the surface. Finally, a method was presented for estimating the yield strength of material, using the hardness values, and it could calculate the yield stress in different passes of process with an acceptable error of 6%.

Machining vibration is one of the most important constraints on productivity. This vibration may cause increase in machining costs, lower accuracy of products, and decrease tool life. Active control is one of the conventional methods for dealing with vibration in machining, but designing an optimized controller for machining process due to unknown parameters in the system is challenging. DVF control method with low computational costs and high capability in increasing the performance of the cutting tool is an effective method, but due to increasing in actuator control input, it can cause actuator saturation; thus, it is not an efficient control method. The aim of this research is implementation of a nonlinear fractional PID controller for increasing effectiveness and improving performance of active vibration control on a boring bar. The results of impact control tests indicate that nonlinear PID control algorithm has good performance in reducing vibrations and increasing the damping of the structure. Using the controller performance criteria, the optimal fractional can be chosen for the nonlinear PID controller, which in addition to increasing the damping of the tool, can reduce the power consumption and, thus, prevent the actuator saturation. The results of the cutting tests also show that the nonlinear PID controller reduces control voltage and actuator power with respect to the DVF controller, which results in improving the boundaries of stable machining. Moreover, during impacts in machining process, such as the initial engagement of the tool, the proposed controller results in a significant reduction in the control voltage peak.

The properties such as weak wear resistance and low hardness of aluminum alloys have limited their use in various industries. In this research, it has been attempted to improve the mechanical and tribological properties of these materials by deposition of nickel-phosphorousalumina functionally graded coating. Functionally graded coatings have been produced by a gradual change in the chemical composition and content of the nanoparticle, using continuous change in pulse parameters such as duty cycle and frequency during the coating process. So, the effect of the duty cycle and frequency has been investigated. Two types of coatings have been created with a gradual decrease in the duty cycle of 90% to 30% and a pulse frequency of 50 to 500 Hz. The result shows that the effect of frequency on the amount of phosphorus and nanoparticles is negligible, and it has mainly affected on grain size. However, in nanocomposite coats, the gradual decrease of duty cycle has led to an increase in the amount of phosphorus (5. 3% to 15. 5 wt. %) and alumina nanoparticles (0. 7% to 2. 6 wt. %) from the substrate to the top surface. With the gradual changes in chemical and microstructure, the adhesion of the coating to the substrate has improved. The results of micro-hardness have also shown that the creation of functionally graded coatings using duty cycle variation has a higher hardness than the one produced by frequency changing. Also, based on the results of the pin test on a disk against abrasive steel 52100, the wear resistance of functionally graded coatings has improved compared to single-layer coatings.

Mechanical variables and properties of soft tissues, such as strain and Young’ s modulus, are estimated by dint of novel methods known as Elastography, for instance, with the aim of improving medical diagnoses, especially the noninvasive detection and classification of tumors. In elastography approach, local mechanical properties of tissues are estimated from their responses to static or dynamic excitations, which are being recorded using conventional medical imaging machines. In the most elastography techniques, for example, strain (static) elastography, displacement fields are generally extracted from the recorded data such as ultrasound images and signals. The profits of cross correlation algorithm, for instance, high precision, accuracy, and resolution, have made it the most prevalent method for estimating strain field in the tissue from the recorded ultrasound signals and images. The benefits of cross correlation method outweigh its defect in the fast computation of displacement and strain field. In this paper, some strategies, specifically the guided search, have been manipulated to improve the speed of algorithm, without decreasing its accuracy. In order to evaluate the proposed stratagem, the ultrasound signals, which had been captured while a cancerous liver was compressing, have been utilized. The average differences between the axial displacement and strain fields estimated by applying the enhanced cross correlation method (calculated in less than 30s) and the analytic minimization technique have been computed 0. 22sample and 0. 21×10-2. Minor disparities between the two sets of displacement and strain field estimated utilizing the aforementioned techniques validate the accuracy of results of the enhanced cross correlation method.

In this study, using volume of fluid method in open source software OpenFOAM, the phenomenon of evaporation in the porous medium was analyzed. At the beginning of the solution, the system consists of a water phase and a porous copper environment. In the next steps of numerical simulation and as a result of partial evaporation of water, the vapor phase appears as the second fluid phase. Water and vapor are assumed to be incompressible and incompatible, and the phenomenon of evaporation occurs unevenly. The interface between phases is modeled by the VOF method and the Lee model has been used to mass transfer between two phases of water and vapor. For surface tension between phases, the continuous surface force (CSF) method was considered. The comparison of simulation results with experimental results showed that the combined solver of porous medium evaporation would well estimate the rate of evaporation at different sections of the channel. In addition, the results of the wall temperature indicate that the channel is divided into two zones of heating and evaporation. In the region of heating, the temperature increases linearly with the channel length to reach saturation temperature. After the point of saturation, the wall temperature first remains constant and eventually forms an oscillatory shape, in which locally there are temperature jumps. The evaporated flow rate also increases at high intensity first, but in the end regions of the porous channel, its growth rate is slow.

Inconel 718 is precipitation strengthened Ni-base superalloy that is strengthened by “ γ ″ precipitate with the Ni3Nb chemical composition, is widely used for medium and high temperature applications in many industries. The aim of this study is to evaluate the effects of pre-cold treatment on microstructure, geometry of weld, Weldability, and mechanism of HAZ liquation cracking in Inconel 718 superalloy by Nd: YAG pulsed laser welding. Microstructure was investigated, using optical microscope and scanning electron microscope and hardness test was used to investigate mechanical properties. The results of numerical calculations using Rosental relation showed that the length of different welding regions including Mushy Zone (MZ), Partially Melted Zone (PMZ), and Heat Affected Zone (HAZ) decreased by 46%, 46%, and 56%, respectively. The experimental calculations also indicated that the length of PMZ and HAZ, as well as the HAZ area decreased by 2. 1, 2. 5, and 2. 5 times, respectively. Considering that grain boundary liquation was observed in all samples, the possible mechanism for HAZ liquation cracking is constitutional liquation of Nb-rich carbides and delta precipitates that encourages the formation of liquid films in the grain boundaries and causes HAZ liquation cracking in this region. Also, the hardness profile indicates that the hardness of the weld metal increased by using pre-cold conditions.

In northwestern Iran, two wells with different temperature and pressure conditions have been exploited in Sabalan region. According to the thermodynamic properties of wells, the integrated cycle (flash integrated cycle with transcritical CO2 and Kalina 11) is proposed for Sabalan geothermal. In the Kalina 11 and transcritical CO2 heat exchangers, in which the fluid temperature is rising, there is a different temperature variation gradient; therefore, a new method is proposed for the determination of pinch point and other thermodynamic properties. The effects of the Kalina high pressure, amoina concentration, transcritical CO2 cycle pressure ratio, pinch points temperature difference, and separators’ pressure on the thermal and exergy efficiencies of the proposed combined cycle were studied. Finally, the proposed combined cycle was optimized thermodynamically, using the EES (Engineering Equation Solver) software. Based on identical operation conditions, the net power of the combined cycle is 20046 kW, the thermal efficiency is 17. 15%, the rate of exergy destructions is 8259 kW, and the exergy efficiency is 65. 74%. It was found that the net power output, the thermal, and exergy efficiencies of combined cycle are about 17. 55%, 17. 55% and 20. 04% higher than the previously proposed system.

In this paper, using a thermodynamic rules, a multigeneration energy system with an initial stimulus of microturbine has been modeled. Then, using the concept of exergy and applying economic and environmental functions, exergy efficiency and total cost rate are calculated as two objective functions. Due to the contradiction of the objective functions, a multiobjective firefly algorithm is used to optimize the system. To accelerate the process of optimization and to prevent algorithm capture in local optimizations, new algorithms have been added to the innovative algorithm. The result of applying the algorithm on the multigeneration energy system will result in a set of Pareto-optimal solutions, indicating the compromise between the target functions. A fuzzy decision making based on max-min approach is used to select the desired solution between the Pareto-optimal solutions. In order to evaluate the efficiency of the proposed optimization algorithm, the results of this algorithm are compared with two particle swarm optimization algorithms and multi-objective genetic algorithm. Based on the results of system optimization, the exergy efficiency can increase up to 69%. Also, considering the total cost rate of the system as the only target function, this can be reduced to 572$/h.

The heat transfer from walls has a significant role in the correct estimation of temperature distribution in order to investigate the thermal stresses and low cycle fatigue in the engine liner. Therefore, it is necessary to investigate the details of the flow and heat transfer over a wide range of engine operation in the design and exact simulation of the cooling jacket. An efficient approach to study the cooling system is to simulate using Computational Fluid Dynamics (CFD) as a three-dimensional model by simultaneously solving the structure and fluid, which leads to accurate prediction of wall temperature and heat flux. In the present paper, the distribution of heat transfer coefficients (HTC) in the cooling jacket of a 16-cylinder heavyduty diesel engine has been calculated, using ANSYS/Fluent based on 3D-CFD method. Also, equations of subcooled boiling phenomenon have been solved based on two commonly used patterns of Chen and BDL, and the effects of fluid pressure, velocity, and temperature at the time of the phenomenon of boiling on the heat transfer of cooling jacket wall have been studied. The results indicate that the best condition for a cooling jacket is when the coolant flow in critical heat points reaches to a velocity so that subcooled nucleate boiling occurs.

Spherical joints are specifically used in many robotic systems, including various industrial and medical applications, especially in non-structured environments. Modular robotic systems are the appropriate solution for use in these environments; So that the configuration of the robots can change quick and easy by link or separate different modules. Flexibility of modules, enough degrees of freedom, capability to stabilize the position of the module and rigidity to maintain strength and stiffness of modular robot during mission are the most important features of a modular robot. Shape memory alloys are suitable actuators for use in robotic modules, which a tiny, lightweight, and without noise system is achieved by using them. In this paper, a mechanism with two degrees of freedom has been created by placing three memory shape alloys springs in the structure of a flexible joint module. Also, with the installation of an electromagnetic system in the joint, it is possible to stabilize its position when necessary. The developed module, in addition to its high flexibility, can maintain its position when needed and increase the strength of the robotic arm. In this research, the design of the module has been presented and kinematic and force analysis has been investigated.

Incidence of breaks and leakages in fluid transportation pipes is a common issue in Iran. Depending on the type of pipes and environmental conditions, the breaks in the pipes may be caused by different factors, including mechanical damages, internal or external corrosions, failures, or applied stresses. In the repair of damaged pipes, there are several strategies for rebuilding and implementing the pipeline, most of which are replacing the entire exhausted pipe, using weld clamps and using composite patches. In recent years, the use of composite patches has been accepted as a low-cost, permanent, and standard method for different pipe sections with the least interruption in transportation. In the present study, the boding strength of glass fibers-reinforced epoxy composite patches on a structural steel substrate were investigated and optimal conditions of achieving enhanced adhesion strength of composite patches on the steel substrate were determined, using the Tagochi method at various curing temperatures and times. In this regard, the tensile and shear strength of epoxy, cyanoacrylate, and methacrylate-based glues as three kinds of appropriate polymers for bonding the epoxy composite on the steel substrates were tested. The mechanical strength measurements and fractured interfaces evaluations using a scanning electron microscopy (SEM) revealed that the methacrylate-based glue has the better adhesion strength to the steel substrate.

Controlling the gas turbine emissions has led the manufacturers to use new technologies. Nitrogen oxides (NOx) are one of the major pollutants of gas turbines with natural gas as fuel. Thermal NOx is the main cause of NOx formation in gas turbines at high temperatures. So, water injection can be useful in reducing the NOx emission. In addition to NOx reduction, water injection causes an increase in carbon monoxide emission and damage to combustion chamber. Therefore, it is desirable to find the optimum amount of water injected to the combustion chamber to meet the regulations. To find the optimal water mass flow rate, we numerically investigated the combustion inside the chamber for full load and part load before and after water injection. Then, the effect of water injection at different flow rates was studied to obtain optimal water flow rate. The results showed that for the full load, the optimal water flow rate was 100% of the fuel flow rate and the upstream pressure of the feed water system was 24. 45 bar. For the part load (fuel flow rate equals to 75% of the full load), the optimum water injection rate is 80% of the fuel flow rate. In this case, the pressure required for water injection is about 16. 5 bar. Results also show that the change in water temperature in the range of 10-80˚ C has no significant effect on NOx formation and water can be injected at the ambient temperature.

New users such as pedestrians are added to navigation systems with developing lightweight, portable, low-cost technologies. The pedestrian navigation systems are currently applied in miscellaneous fields including medicine, sport, military services, animation, robotics, etc. This amount of use has attracted the attention of many scholars over the last few decades. In this paper, the paths of a firefighter, as a pedestrian, was estimated approximately by the help of an inertial measurement unit (IMU) and acceleration sensors. To reduce the measured errors and noises by the sensor, zero velocity update (ZUPT) method and Kalman filter are exploited in a pedestrian navigation system. Due to the fact that the error in blind navigation is divergent over time if the filter is not used, the use of conventional accelerometer sensors cannot produce a satisfactory result. using the combined module of an inertial measurement sensor that includes accelerometer and gyroscope, it is possible to track the person’ s position at any moment while the sensor is tracked on the shoe. The ability of ZUPT in navigation system has been discussed and interpreted by measuring a path using a sensor installed on a person’ s shoe and comparing the results with the desired predetermined path.

In this paper, a study from the perspective of exergy and cost in the framework of exergoeconomic analysis of a heating and power generation system with parabolic trough solar collectors was carried out as a case study to be used at the engineering faculty of Urmia University. The system consists of a solar subsystem with an Organic Rankine Cycle (ORC). This study is based on three different solar radiation modes during a day, including solar mode, solar and storage mode, and storage mode. In the first mode, the solar flux is at a low level and there is no energy storage. In the second mode, there is energy storage in addition to running the ORC by collectors. In the third mode, only storage tank is used. Paying attention to the actual energy demand of the location and the analysis according to the variable solar radiation are the important points of this study. Due to the weather conditions prevailing on the building, its heating load is 1253. 2 kW. Also, the electric power required is about 1500 kW. Exergoeconomic analysis is based on three important design parameters, including the number of the day through the year, ORC pump input temperature, and ORC turbine inlet pressure examined. The results indicate that in a cold day, the cost per unit of exergy in the three mentioned modes are about 19 $/GJ, 16 $/GJ, and 20 $/GJ, respectively. Also, the highest exergy destruction rate occurs in parabolic trough solar collectors and ORC evaporators.

Vibration of various types of structures such as beam, plate, shell, and rod have been investigated by researchers for their application in a wide range of mechanical systems. The longitudinal vibration of the rods is of great interest, so that the researchers have performed them numerically or analytically and precise or approximate. In this research, the nonlinear longitudinal free vibration of rod with variable cross-section under finite strain has been investigated. First, the governing equations of the rod with variable cross-section were obtained, which are partial differential equations; then, they were transformed to nonlinear ordinary differential equations, using the Galerkin method with considering one mode shape. The problem was investigated for two boundary conditions. Using the multiple scales method, the equations were analytically solved. The differential equations are solved by Runge-Kutta numerical method of order 4, and then compared with the analytical solutions. The effect of the amplitude and rate of changing cross-section on the ratio of linear to nonlinear frequency and also the effect of different initial condition, rate of changing cross-section and coefficient of damper were shown in figure. The results show that the tapered cross-sectional area has a significant effect on the ratio of linear to nonlinear frequency to vibrations amplitude. The coefficient of damper has a little effect and initial condition has a considerable effect on the process of problem.

With regard to the industry demand for welding dissimilar metals, which are not possible to be welded by conventional welding, friction welding process can be a proper approach. In this study, friction welding of two stainless steels, martensitic 410 to austenitic 304, with variable parameters of friction time (40, 50, and 40 s), friction force (90, 100, and 120 kN), and forging force (130, 150, and 180 kN), under the constant rotating speed (850 RPM) and forge time (60 s) was investigated. Microscopic characterization using optical and scanning electron microscopes, and elemental analysis using energy dispersive X-ray spectroscopy were carried out on the welds. Soundness of the weld joints was evaluated, using tensile and microhardness tests. Fracture surfaces of the tensile specimens were examined as well. The structure of the welded samples composed of acicular and rough martensite and elongated grains adjacent to 410 and 304 stainless steels, respectively. Tempering heat treatment locally caused converting rough martensite to lath martensite. The results showed that the tensile strength of the samples was in the range of 400-520 MPa, and the fractography revealed the occurrence of a brittle fracture. Microhardness measurement revealed that the highest hardness value was obtained in 410 stainless steel, at the heat-affected zone close to the interface. An appropriate friction weld joint with a tensile strength of 751 MPa was obtained after heat treatment of the weld location, and with the aid of selecting optimal parameters of 50 s friction time, 120 kN friction force, and 180 kN forging force.

Today, the effects of three-dimensional flow near the blade and wing tip in the turbomachinery industry, such as rotor helicopters, turbine, as well as wings optimization in the airline industry, for safe flight with high maneuverability, are the focus of the industry in this area. Stall can be considered an influential phenomenon in this field. In the present study, the flow separation control was investigated by a vortex generator on a wing of a radar invader UAV, including a Naca64a210 airfoil with a 5° washout angle at the wing tip and integrated wings and attached to the body with a 47° sweep angle in the subsonic flow. The turbulent flow was solved by the kw-sst method for attack angles ranging from 5-20° and speeds of 30 and 60 m/ sec. The results show a good fit with numerical and experimental results, so that the pressure distribution curves indicate the growth of pressure in the vortex generating regions and also the areas near the tip of the wing, which results in the flow remain in the wing surface in these areas. Therefore, by examining the pitching moment and velocity contours, it can be seen that the flow separation from the 15° angle of attack, has been delayed to 20° , and also the ability to control the separation of flow along with the growth of velocities has been achieved.

Hydro screw is a small micro hydro turbine. Due to increase in demand for clean energy production, a comprehensive project at the Iranian Research Organization for Science and Technology (IROST) for the design and construction of very small turbines (micro turbines), including hydro screw, has been developed. Hydro screw is suitable for a low head and discharge that does not have a guide vane and draft tube; thus, it is simple, small, inexpensive, and portable. This turbine, with a 15 cm blade diameter, can generate power up to 2 kW. Hydro screw blade is inspired by the Archimedes turbine, and difference between them is that the blade pitch of hydro screw is variable and horizontally mounted. In this project, the effect of spiral variable pitch on turbine has been studied numerically. Based on the results, it was found that the turbine had the best efficiency at a spiral pitch of 1. 5. Subsequently, the small model of hydro screw was made and tested in the laboratory. The results of this study have been presented in the form of standard curves of turbine performance and the accuracy of the results has been proved by comparison of numerical and experimental results. The results show the integrity of the numerical calculations and, therefore, they can be used in line with next turbine studies. The results indicate that the maximum turbine output is between 62% and 68%.

The structural vibrations are the important sources of the energy harvesting, which can be produced from the harmonic excitation. The piezoelectric structure behavior is simulated by the electromechanical coupling. The flexible beam has the large strain. The results of linear theories are not proper. The large strains effect on the results response and the nonlinear behavior must be considered. The Newmark method is used to solve the equations of motion and coupled equations. Regarding the type of proportional damping, the nonlinear hardness effect is also applied to the damping calculation. This paper presents the electric response of the piezoelectric nonlinear beam with the harmonic base excitation by the numerical and experimental methods. The program of finite elements is developed for the numerical results and the electric response is obtained. The theories results are verified by the results of experimental. The experimental results are used for the piezoelectric bimorph beam with the change of concentrated mass position. The effect of piezoelectric property in the frequency response of nonlinear beam is presented. The results show the effect of piezoelectric properties on the frequency response of the nonlinear beam and the effect of the concentrated mass position on the output voltage, and the most suitable position of the concentrated mass position is presented to obtain the highest voltage response.

Because of the widespread application in complex modeling based on experimental data, neuro-fuzzy networks have attracted the attention of researchers. In the neuro-fuzzy inference system, the objective is to reduce the system’ s prediction error relative to the actual data. The regulation of parameters of neuro-fuzzy network is very important and affects its performance. So, a new optimization algorithm based on Particle Swarm Optimization (PSO) and Differential Evolution (DE) has been proposed. In this algorithm, the coefficients of the operator speed are calculated dynamically, using fuzzy logic. These coefficients are set according to the generation number and variance of the particles. Proposed operator leads the particles to explore and exploit the search domain more precisely. Next, the performance of the proposed algorithm is checked by optimizing three benchmarks and comparing it with the results, which are obtained by conventional PSO and DE. The results show that the proposed algorithm obtained better solution in comparison with DE and PSO and proved its performance and efficiency. Finally, a neuro-fuzzy system has been employed to forecast the time series of Mackey-Glass. The parameters of this neuro-fuzzy network are optimized by the new algorithm and the PSO and DE method multi-objectively and the Pareto charts obtained by each method of optimization are compared with each other, indicating the better performance of the new algorithm.

Acoustofluidics, the study of acoustics in microfluidic systems, is the basis for analyzing many laboratory applications including the separation of particles, particle sorting, cleaning, and mixing multiphase systems. In this research, a three-dimensional finite element model for particle motion under acoustic radiation force in acoustic microchannels is developed and the interaction of the incident waves with a suspended particle in microchannel is investigated. Using finite element method, the first-order fields due to an applied standing wave are initially calculated and, then, the acoustic radiation force is directly calculated from the second-order perturbation equations. The simulation results for radiation force are first verified against the analytical solution in the Rayleigh limit and, then, examined beyond this limit, for which there is no explicit analytical solution. In addition, the quasi-static motion of a particle under the influence of an applied acoustic standing wave in microchannel is simulated. For simulating particle motion, the acoustic stress on particle surface is calculated and transferred as an input to the laminar flow equations. Then, the drag force is estimated based on the shear stress due to the flow around the particle. The simulation results demonstrate that the particle velocity depends on its position with respect to the wave node at the center of the microchannel. As the particle approaches to the center of microchannel, its velocity decreases until it stops at the center of microchannel.

In this paper, a robust discrete control law is presented, using time delay control method for an omnidirectional mobile robot in the presence of system uncertainties. Although time delay control method has attracted the great attention of researchers due to its structure simplicity, the major part of these research have been performed by the assumption of continuous time delay control and infinitesimal time delay that is in contradict of physical nature of digital devices, as implementation tools of time delay controllers, which have finite and specific sample time. Also, the discretization of continuous-time systems has been usually done by Euler estimation method, which has sufficient accuracy for infinitesimal sample times. So, in this paper, after modeling the robot, considering the dynamics of robot motors, a new method for more accurate discretization of continuous nonlinear systems is presented and, then, a robust discrete control law is designed, using the backstepping technique at the voltage level of the robot motors. In the design of control law, a new adaptive sliding mode method is used to overcome the system uncertainties and stability of the closed-loop system is proved by error convergence to a small neighborhood of zero. The proposed controller is designed in the discrete domain without the necessity of being known the bound of system uncertainties and simulation results represent the desired performance of the controller in trajectory tracking.

The cold roll bonding (CRB) is a solid state welding process for bonding similar and dissimilar metals. The use of materials produced by the CRB method for different applications and the prediction of their behavior in simulation software requires the complete and accurate identification of their mechanical properties. Digital image correlation (DIC) is a powerful noncontact method for measuring the field of material deformation. Recently, the DIC method has been developed and widely used in various studies due to its advantages. In this research, twolayered aluminum alloy 1050 was produced via CRB process with applying 50% reduction of thickness at ambient temperature and then using the 2D-DIC system to extract distribution of the strain field during the uniaxial tensile test at rolling direction. Strain in two directions of length and width was calculated, using DIC and strain in terms of thickness, effective strain, and anisotropy coefficient, using plasticity relationships. Moreover, for the first time, using the virtual field methods (VFM), elastic and plastic parameters such as elastic modulus, Poisson ratio, strength coefficient, strain hardening exponent, and yield stress were calculated. The results showed that the strength and microhardness were significantly increased due to the work hardening and increasing the density of dislocations, and the elongation and strain hardening exponent were reduced. The strength for the two-layered aluminum was 113MPa, which improved more than three times of the initial aluminum. Also, changes in the elastic parameters were very small and the modulus of elasticity for the primary aluminum and twolayered aluminum was 69. 3 and 70GPa, respectively.