Alireza Fathi

Architecture optimization of 4PUS+1PS parallel manipulator

The main goal of this paper is the design of 4PUS+1PS parallel manipulator, using an optimization problem that takes into accounts the characteristics of the workspace and dexterity. The optimization problem is formulated considering constraints on actuated and passive joint limits. A comparison between quantum particle swarm Optimization (QPSO) and PSO is developed. Two numerical examples are presented, which reveal the advantages of QPSO to PSO. Moreover, it is shown that by introducing the dexterity index as a quality measure throughout the workspace, the parallel manipulator is improved at the cost of a minor reduction in its workspace.

Enhanced hardness and electrical properties of copper nanocomposites reinforced by functionalized MWCNTs

Functionalized multiwall carbon nanotubes (MWCNTs)-reinforced copper (Cu) nanocomposites have been fabricated by the combination of ball milling and hot-press sintering methods. The functionalization was carried out in two levels under reflux condition. Characterization of the fabricated nanocomposites revealed that the functionalization plays an important role in enhancing the hardness and electrical properties of nanocomposites. Enhancements of up to ∼116% and ∼58% in microhardness compared to pure un-milled and milled Cu were observed by adding 1 wt.% functionalized MWCNTs. On the other hand, the electrical resistivity of nanocomposites increased by increasing MWCNT contents. It was found that improved control of the Cu and MWCNT interface also leads to enhance electrical properties. Based on the experiments, the results indicated that the amount of chemically bonded oxygen atoms affects the electrical resistivity of nanocomposites. Accordingly, the nanocomposite containing 1 wt.% MWCNTs with lower amount of functional groups has lower electrical resistivity.

Control of aeroelastic characteristics of cantilever wing with smart materials using state-dependent Riccati equation method

In this work, aeroelastic control of a cantilever wing with embedded shape memory alloy wires and piezoelectric actuators is carried out. Shape memory alloy wires increase the total stiffness of the system by generating an in-plane load, and they are used as passive controllers. Piezoelectric actuators are used for active control of a fluttering plate using the state-dependent Riccati equation method. The effect of shape memory alloy wires and piezoelectric actuators on the aeroelastic flutter condition and limit cycle oscillation amplitude of a rectangular cantilever wing are investigated. Wings are modeled according to the first-order shear deformation plate theory and large deflection Von Karman plate theory. Simulation results are presented, which show that the designed state feedback control law can be used for the stabilization of an aeroelastic system with structural nonlinearities.

Experimental analysis of a low-cost dead reckoning navigation system for a land vehicle using a robust AHRS

Abstract In navigation and motion control of an autonomous vehicle, estimation of attitude and heading is an important issue especially when the localization sensors such as GPS are not available and the vehicle is navigated by the dead reckoning (DR) strategies. In this paper, based on a new modeling framework an Extended Kalman Filter (EKF) is utilized for estimation of attitude, heading and gyroscope sensor bias using a low-cost MEMS inertial sensor. The algorithm is developed for accurate estimation of attitude and heading in the presence of external disturbances including external body accelerations and magnetic disturbances. In this study using the proposed attitude and heading reference system (AHRS) and an odometer sensor, a low-cost aided DR navigation system has been designed. The proposed algorithm application is evaluated by experimental tests in different acceleration bound and existence of external magnetic disturbances for a land vehicle. The results indicate that the roll, pitch and heading are estimated by mean value errors about 0.83%, 0.68% and 1.13%, respectively. Moreover, they indicate that a relative navigation error about 3% of the traveling distance can be achieved using the developed approach in during GPS outages.

Formation of homogenous copper film on MWCNTs by an efficient electroless deposition process

Abstract In this study, copper-coated multi-walled carbon nanotubes (MWCNTs) were prepared using electroless deposition process with an efficient bath composition. As-received MWCNTs underwent acid treatment and subsequent sensitization with tin and activation with palladium before the copper coating process. The electroless deposition process was performed in a bath, which contained copper sulphate pentahydrate as a copper precursor, potassium sodium tartrate as a complexing agent, and formaldehyde as a reducing agent. Surface modifications of MWCNTs were studied by Fourier transform infrared spectroscopy, imaging techniques (scanning electron microscopy, transmission electron microscopy), and X-ray diffraction. On the basis of the results, it was observed that the coating layer covers most surfaces of the nanotubes. Furthermore, copper oxide is also deposited on the surfaces of MWCNTs. The total amount of metals after each sensitization, activation, and metallization step was determined by thermo gravimetric method and induced coupled plasma atomic emission spectroscopy. Coating of MWCNTs was accomplished successfully through adjusting proper chemical ratios and concentrations. The calculated bath efficiency was about 99%.

Free vibration analysis of a shape memory alloy beam with pseudoelastic behavior

The present contribution deals with developing a semi-analytical analysis for studying the free vibration of a shape memory alloy beam with pseudoelastic behavior. The equations of motion are derived using the Hamilton principle and the Euler–Bernoulli theory. Then mathematical processes of non-dimensionalization and numerical integration are performed and finally the obtained partial differential equations are solved using the Galerkin method. A three-dimensional phenomenological model for shape memory alloy, which has the capability of identifying the martensite phase transformation, saturated phase transformation, pseudoelasticity and the shape memory effect, is utilized for modeling the shape memory alloy. According to the hysteresis behavior of the shape memory alloy, the energy dissipation characteristic is clearly observed in the early stages of the free vibration. Stress and strain analysis is employed to specify the effect of phase transformation in each layer along the beam. The property of shape memory alloy beam demonstrates its great potential for using in damping applications.

Effect of CO2 laser power intensity on the surface morphology and friction behavior of alumina ceramic brackets

This study aims at reducing frictional resistance of the ceramic brackets by using CO2 laser irradiation.

Vibration Analysis of a Beam with Embedded Shape Memory Alloy Wires

In this study, analytical relations for evaluating the exact solution of natural frequency and mode shape of beams with embedded shape memory alloy (SMA) wires are presented. Beams are modeled according to Euler-Bernoulli, Timoshenko and third order beam (Reddy) theories. A relation is obtained for determining the effect of axial load generated by the recovery action of pre-strained SMA wires. By defining some dimensionless quantities, the effect of different mechanical properties on the frequencies and mode shapes of the system are carefully examined. The effect of axial load generated by SMA wires with buckling load and frequency jump is accurately studied.

Numerical study of the stand-off distance and liner thickness effect on the penetration depth efficiency of shaped charge process

The aim of this paper is to investigate the effect of geometrical parameters on the performance of jet penetration in the process of shaped charge. To this end, the finite element analysis was used to simulate the process. The simulated process was validated by experimental tests and the effect of some parameters including stand-off distance and the liner thickness on the jet penetration depth was studied. The results indicated that choosing the optimal distance between the liner and the target (stand-off distance) can significantly affect the performance of jet penetration in the target. In addition, examining the effect of liner thickness on the penetration depth efficiency revealed that by decreasing the liner thickness, the jet penetration depth on the target increases. It should be noted that ABAQUS finite element software was used in this simulation to analyze the process of shaped charge.