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Feed provided by ADMT Journal. Click to visit.Direct Kinematics Solution of 3-RCC Parallel Robot using a Semi-Analytical Homotopy Method
http://admt.iaumajlesi.ac.ir/article_664197_1132797.html
Parallel robots are closed-loop mechanisms presenting very good performances in terms of accuracy, rigidity, and the ability to manipulate large loads. Inverse kinematics problem for most parallel robots is straightforward, while the direct kinematics is not. The latter requires the solution of the system of nonlinear coupled algebraic equations and has many solutions. Except in a limited number of these problems, there is difficulty in finding exact analytical solutions. So these nonlinear simultaneous equations should be solved using some other methods. Continuation or path-following methods are standard numerical techniques to trace the solution paths defined by the Homotopy. This paper presents the direct kinematics solutions for a 3RCC parallel robot by using a semi-analytical Homotopy method called Homotopy Continuation Method (HCM). The HCM has some advantages over the conventional methods and alleviates drawbacks of the traditional numerical techniques, namely; the acquirement of good initial guess values, the problem of convergence and computing time. The direct kinematic problem of the 3RCC parallel robot leads to a system of nonlinear equations with 9 equations and 9 unknown parameters. The proposed method solved these nonlinear equations and extracted all the 36 solutions. Results indicate that this method is effective and reduces computation time in comparison with the Newton–Raphson method.Thu, 28 Feb 2019 20:30:00 +0100Optimal Design of a Novel Two-Branch Spray Painting Robot for Prescribed Process Space
http://admt.iaumajlesi.ac.ir/article_664199_1132797.html
Painting of roadside blocks manually is costly and time-consuming and can cause road accidents for workers. This paper is devoted to the optimum design of a novel two-branch robot utilized as spray painting mechanism for side and top of the roadside blocks simultaneously. Considering painting process conditions and the block displacement pattern which can change both height and lateral location along the road, clear that the process could be carried out properly by means of two nozzles. Two planar process spaces are evolved in favour of two-dimensional paths where nozzles track during the process. A conceptual architecture is formed considering the same movements that nozzles are actuated to compensate the blocks’ horizontal displacements. One parallel and one serial manipulator of the robot structure a relation by common prismatic joint. Actuators are positioned close to the base of the truck so that dynamics of movable parts are to be improved logically. Due to the change in the height and lateral location of the blocks, position of joints be optimized in terms of stroke angle and process space could be best fitted into workspace, optimization problem is arisen and solved using Genetic algorithm (G.A.) which results in less angular stroke for lower nozzle and faster matching with block conditions. The optimized joint position and center of mass are far from the base, resulting in a large torque subjected to the base. To solve the problem, the joint position is shifted toward the base without a change in the optimum situation. Finally, results are studied and detailed further. Thu, 28 Feb 2019 20:30:00 +0100Modelling of Non-Uniform Piezoelectric Micro-Cantilever in Different Environments
http://admt.iaumajlesi.ac.ir/article_664287_1132797.html
In recent years, Atomic Force Microscopy (AFM) has been known as a powerful and efficient tool for surface imaging in different environment. To enhance image quality and more precise prediction of Micro-cantilever (MC) behaviour, accuracy in the MC modeling and simulation and detecting the MC sensitivity to geometric parameters has great importance. To model the vibration motion of the AFM non-uniform piezoelectric MC, Timoshenko beam theory is used in order to consider the effect of shear effect in air and liquid environment. In addition, the effect of the forces imposed by the ambient and sample surface is considered. Frequency response has been studied in the air and different liquid environments and the obtained results have been compared with experiential results as well as with results obtained from Euler-Bernoulli beam theory that is reflective of higher precision exercised in the modeling in respect to Euler-Bernoulli beam theory. Efast statistical method, which is found efficient and quick in the survey of linear and nonlinear models and takes the inter-parameter coupling effect into consideration besides calculating the sensitivities unique to each of the factors, has been applied in order to analyse the geometrical parameters’ effects on the MC natural frequencies in the air and water environments.Thu, 28 Feb 2019 20:30:00 +0100Qualification of Propeller by Experimental and Analytical Methods
http://admt.iaumajlesi.ac.ir/article_664201_1132797.html
The paper focuses on static and dynamic analysis of propeller blade made of Aluminium-24345 material. The solid model of propeller blade and propeller are developed in CATIA V5 R20. By using this model, propeller blade was manufactured using 3-Axis CNC milling machine by adopting MASTERCAM software. Qualification tests were carried out on the propeller blade of an underwater vehicle for their strength and vibration. Impact Hammer Method is employed to measure the vibration-damping properties of Propeller blade. Computational Fluid Dynamics (CFD) analysis is carried out to analyze the contours of static pressure on the 5-Blade propeller and the forces, moments acting on the propeller. Finite element analysis (FEA) of the blade was carried in ANSYS 15.0. Static, modal, harmonic analysis was carried out on analysis software for the modeled propeller blade and factor of safety was determined to qualify the propeller. Deformation of the propeller blade is measured using Coordinate Measuring Machine (CMM).Thu, 28 Feb 2019 20:30:00 +0100Optimal Design of Steppers in Single Step High Pressure Torsion (SIHPT) Process as a Novel SPD ...
http://admt.iaumajlesi.ac.ir/article_664202_1132797.html
Single Step High Pressure Torsion (SIHPT) is a newly developed HPT based method for processing of materials which is capable of producing nanostructured long samples with characteristics comparable to conventional HPT process. While, conventional HPT can be applied only on thin samples; it is possible to produce nanostructured parts with about 10 cm long using SIHPT method. However, SIHPT needs some technical improvements in order to be used for production in an industrial scale. One of the key component of SIHPT is the steppers which help different sections of the sample to be twisted. This study investigates the main parameters of steppers including the corner radius, thickness and rotation speed. The experimental results revealed that for the lowest length of sample’s contact inside the steppers (lower contact length) of 5mm; there is considerable slippage in pressures below 1GP. However, the amount of slippage decreases gradually by increasing the magnitude of the applied pressure and the amount of the lower contact length. Moreover, it was found that the rotational speed influences the amount of slippage in low pressures (lower than 1 GPa) but not in high pressures. In addition, according to Finite Element (FE) analysis it was found that 1 mm corner radius of steppers is the optimal value for the SIHPT process. Thu, 28 Feb 2019 20:30:00 +0100Multi-Objective Optimization of Loading Paths for Double-Layered Tube Hydroforming using Finite ...
http://admt.iaumajlesi.ac.ir/article_664203_1132797.html
One of the most important studies in tube hydroforming process is optimization of loading paths. The primary purpose of this research is to maximize formability by detecting the optimal forming parameters. The most significant settings in the prosperity of tube hydroforming process, are internal pressure and end axial feed (i.e., load path). In this paper, a finite element analysis was performed for a double-layered tube hydroforming process using the ABAQUS/Explicit software. Then, the finite element model has been verified with published experimental data. Using design of experiments (DOE) working with the Taguchi method, 32 loading paths are designed for optimization. All 32 loading paths are modelled using the finite element method in ABAQUS/Explicit and the magnitudes of bulge height and the total thickness of tubes at the branch tip are obtained in each loading path. The regression analysis is carried out to estimate the tubes formability and obtain objective functions that are bulge height and the total thickness of tubes at the protrusion peak as functions of loading parameters (internal pressure and axial feed). For solving the multi-objective optimization problem, the non-dominated sorting genetic algorithm II (NSGA-II) is utilized and the optimum results were obtained from the Pareto optimal front. Finally, the optimized loading path was applied to the finite element model and better formability (3.4% increase in the bulge height) has been achieved in the results. Thu, 28 Feb 2019 20:30:00 +0100Impact of Loading Rate in Hot Tube Gas Forming of AA6063
http://admt.iaumajlesi.ac.ir/article_664204_1132797.html
In this paper, the manufacturing of a cylindrical AA6063 step tube via hot metal gas forming (HMGF) process is studied both experimentally and numerically. The goal is to investigate the effect of loading rate on the specimen profile and thickness distribution. ABAQUS finite element software is used for the numerical simulation. Experiments were carried out at 580°C in two conditions; first, without axial feeding and then with an axial feeding of 14 mm at a maximum pressure of 0.5 MPa. The studied parameters are the pressure rate and the axial feeding rate. The results show that in the non-axial feeding mode, the thickness distribution in the die cavity region was non-uniform and a rupture occurred at a pressure of 0.6 MPa. The reduction of the pressure rate has no significant effect on the rupture pressure. In the case of axial feeding, by choosing the pressure rate of 0.001 MPa/s and the axial feeding rate of 0.1 mm/s, wrinkling has been created in the specimens. However, at a pressure rate of 0.005 MPa/s and an axial feeding rate of 0.02 mm/s, the specimens are raptured. Under low pressure rate of 0.001 MPa/s and low axial feeding rate of 0.02 mm/s, the thickness in the die cavity area has decreased. A suitable die filling and thickness distribution are obtained at a pressure rate of 0.005 MPa/s and axial feeding rate of 0.1 mm/s.Thu, 28 Feb 2019 20:30:00 +0100Determination of Local Constitutive Properties of Aluminum using Digital Image Correlation: A ...
http://admt.iaumajlesi.ac.ir/article_664294_1132797.html
A proper understanding of material mechanical properties is important in designing and modelling of components. As a part of a study on the structural integrity, the Digital Image Correlation technique was used to obtain the full-field strain distribution during a tensile test of the specimens. In this study, the elastic and plastic properties of Al6061 alloy has been carried out using both the uniform stress method and the virtual fields method involving digital image correlation technique. In uniform stress methodology, full range stress–strain curves are obtained using the whole field strain measurement using Digital Image Correlation. Recently, the virtual fields method is gaining a lot of popularity in domain characterization as it is robust, accurate and faster. Young's modulus, Poisson's ratio, yield strength, strength coefficient and strain hardening exponent are the parameters extracted using both uniform stress method and virtual fields method. The parameter variation obtained by both uniform stress method and the virtual fields method are compared very well. The Virtual Fields Method provides a theoretically sound basis for developing robust optimization constructs to estimate local material properties, including spatial variations in hardening exponent and strength coefficient. Due to various advantages associated with virtual fields method, it is generally recommended for material mechanical properties extraction. Thu, 28 Feb 2019 20:30:00 +0100Effect of the Number of Welding Passes on the Microstructure and Wear Behavior of St52 Plain ...
http://admt.iaumajlesi.ac.ir/article_664710_1132797.html
This study investigated the effect of the number of welding passes on the microstructure, hardness, and wear behavior of St52 plain carbon steel coated with an E10-UM-60R electrode in accordance with the DIN 8555 standard using SMAW method. An optical microscope (OM) and a scanning electron microscope (SEM) were used, and an EDS analysis was carried out to examine the microstructure. The Vickers micro hardness test and a reciprocating wear test were also used to examine the hardness and wear resistance. The results showed that the structure on the surface of the coated specimens is consisted of M7C3 carbides in the eutectic field (). In addition, the volume fraction of carbides increased in specimens that underwent two passes of welding relative to that in one pass-welded specimen. The reason for this was related to the decreased dilution of iron and increased dilution of chromium in the two-pass welded specimen and an increase in the volume fraction of M7C3 carbides. The increased percentage of carbides in the two-pass welded specimen increased the hardness and consequently the wear resistance relative to those in the one-pass welded specimen in a way that the surface hardness and weight loss in the wear test reached from 780 HV and 3.7 mg in the one-pass welded specimen to 910 HV and 2.5 mg in the two-pass welded specimen. Moreover, examining the wear surfaces indicated the occurrence of an adhesive wear mechanism in the specimens in a way that the adhesive wear rate decreased in the two-pass welded specimens.Thu, 28 Feb 2019 20:30:00 +0100Evaluating the Effects of Overload and Welding Residual Stress in Fatigue Crack Propagation
http://admt.iaumajlesi.ac.ir/article_664711_1132797.html
In this paper, a suitable method is presented to predicate fatigue crack propagation for cyclic loading with overload in residual stresses field resulted by weld. For this, first effective stress intensity factor (SIF) and effective cycle ratio (R) are introduced as function depending on SIFs resulted by external load, weld residual stress and overload. Weight function is applied to calculate SIF resulted by weld residual stress. Also, a method is introduced to determine overload SIF and overload stress ratio. Then fatigue crack propagation equation is modified for our purpose. In other words, a simple and efficient method is presented in this paper for predicting fatigue crack propagation rate in welded joints when the overload is happening. Finally, for evaluating this modified equation, experimental methods are applied. Test samples were M(T) geometry made of aluminum alloy with a longitudinal weld by the Gas Tungsten arc welding process. Modified equation has a good agreement with the experimental model presented in this field.Thu, 28 Feb 2019 20:30:00 +0100