Amirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Experimental and Numerical Determination of Fracture Toughness in Gas Pipeline Steel of Grade API X65Experimental and Numerical Determination of Fracture Toughness in Gas Pipeline Steel of Grade API X651931610.22060/mej.2013.316FAS. H.HashemiMasoudKymyabakhshJournal Article20140619Plain strain fracture toughness is extremely important for failure assessment in high strength steels used in gas transmission pipelines. In the current research an experimental method based on three point bend test specimens was used to calculate fracture toughness of steel pipes of grade API X65 (with outer diameter of 1219 mm and wall thickness of 14.3 mm). A value of 308 MPa√m was found for fracture toughness of test material. Then a finite element solution for the test specimens was conducted using modified Gurson’s damage theory. In this model, the critical crack tip opening displacement was calculated from damaged elements in the early stage of crack growth. This model resulted in 297 MPa√m of fracture toughness. A comparison between the experimental and numerical results illustrated the fitness of common methods for determining fracture toughness of tested steel in ambient temperature. Due to the lack of experimental data for this steel, the obtained results can be used for safe performance of domestic gas pipelines made from API X65 steel. <br /> Plain strain fracture toughness is extremely important for failure assessment in high strength steels used in gas transmission pipelines. In the current research an experimental method based on three point bend test specimens was used to calculate fracture toughness of steel pipes of grade API X65 (with outer diameter of 1219 mm and wall thickness of 14.3 mm). A value of 308 MPa√m was found for fracture toughness of test material. Then a finite element solution for the test specimens was conducted using modified Gurson’s damage theory. In this model, the critical crack tip opening displacement was calculated from damaged elements in the early stage of crack growth. This model resulted in 297 MPa√m of fracture toughness. A comparison between the experimental and numerical results illustrated the fitness of common methods for determining fracture toughness of tested steel in ambient temperature. Due to the lack of experimental data for this steel, the obtained results can be used for safe performance of domestic gas pipelines made from API X65 steel. <br /> https://mej.aut.ac.ir/article_316_3fe94a002317b5f9259f82690aeea4cd.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Static Analysis of Bending, Stability, and Dynamic Analysis of Functionally Graded Plates by a Four-Variable TheoryStatic Analysis of Bending, Stability, and Dynamic Analysis of Functionally Graded Plates by a Four-Variable Theory112531710.22060/mej.2013.317FAFaridKavianiH. R.MirdamadiJournal Article20140619In this article, static analysis of bending, elastic stability, and free vibration analysis of functionally graded plates (FGP) are investigated using a four-variable theory. In this four-variable theory, hyperbolic sine distribution is used for satisfying boundary conditions of out-of-plane shear stresses of zero value, in the neighborhood of upper and lower surfaces of plate. One of the mechanical characteristics of FGM material is continuous variations of properties along the thickness, with a power law distribution, which is a function of volume ratio of different constituent parts of FGM plate. The purpose of this article is acquiring more exact analytical results than those of simple form of four-variable plate theory, i.e., refined plate theory (RPT). Furthermore, for parametric study, influential parameters on the analysis of FGM plate are investigated. The plate equations of motion are derived by extended Hamilton’s variational principle. Analytical results are developed based on classical method of Navier and simply-supported conditions on all four edges. Numerical results are analyzed for different power distributions of mechanical properties along the thickness and different plate length to thickness ratios. The results, obtained from this theory, are compared with those of different variants of RPT theories.In this article, static analysis of bending, elastic stability, and free vibration analysis of functionally graded plates (FGP) are investigated using a four-variable theory. In this four-variable theory, hyperbolic sine distribution is used for satisfying boundary conditions of out-of-plane shear stresses of zero value, in the neighborhood of upper and lower surfaces of plate. One of the mechanical characteristics of FGM material is continuous variations of properties along the thickness, with a power law distribution, which is a function of volume ratio of different constituent parts of FGM plate. The purpose of this article is acquiring more exact analytical results than those of simple form of four-variable plate theory, i.e., refined plate theory (RPT). Furthermore, for parametric study, influential parameters on the analysis of FGM plate are investigated. The plate equations of motion are derived by extended Hamilton’s variational principle. Analytical results are developed based on classical method of Navier and simply-supported conditions on all four edges. Numerical results are analyzed for different power distributions of mechanical properties along the thickness and different plate length to thickness ratios. The results, obtained from this theory, are compared with those of different variants of RPT theories.https://mej.aut.ac.ir/article_317_5b8add2a5d98b1a652ea7fd72d942dac.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Dynamic Response of Sandwich Panels with Flexible Cores and Elastic Foundation Subjected to Low-Velocity ImpactDynamic Response of Sandwich Panels with Flexible Cores and Elastic Foundation Subjected to Low-Velocity Impact274231810.22060/mej.2013.318FAKeramatMalekzadeh FardGholamhosinPayganehMansourKardanJournal Article20140619In this paper, for first time dynamic response of composite sandwich panel with a flexible core on elastic foundation under low-velocity impact load is studied. The governing equations of sandwich panel are obtained using the Hamilton principle and energy method. Free vibration analysis of panel is based on the improved higher-order sandwich panel theory (IHSAPT) by considering elastic foundation effects in equations. The formulation uses the first shear deformation theory (FSDT) for face sheets and Frostig’s second model for core. The equations system is solved for plate on elastic foundation using two parameters Pasternak model. For dynamic analysis of composite sandwich panel under low-velocity impact load, the sandwich panel is modeled as a two-degrees-of-freedom dynamic system with equivalent masses and springs using linearized Hertz contact law from Choi method. In this model for impact solution, fundamental natural frequency has been used directly for calculation of the equivalent stiffness of panel. Effect of variation of various vertical and transverse shear modulus of elastic foundation on natural frequencies of free vibration, contact force history and transverse displacement of panel in low-velocity impact analysis is discussed and is compared with the available results in literature. In this paper, for first time dynamic response of composite sandwich panel with a flexible core on elastic foundation under low-velocity impact load is studied. The governing equations of sandwich panel are obtained using the Hamilton principle and energy method. Free vibration analysis of panel is based on the improved higher-order sandwich panel theory (IHSAPT) by considering elastic foundation effects in equations. The formulation uses the first shear deformation theory (FSDT) for face sheets and Frostig’s second model for core. The equations system is solved for plate on elastic foundation using two parameters Pasternak model. For dynamic analysis of composite sandwich panel under low-velocity impact load, the sandwich panel is modeled as a two-degrees-of-freedom dynamic system with equivalent masses and springs using linearized Hertz contact law from Choi method. In this model for impact solution, fundamental natural frequency has been used directly for calculation of the equivalent stiffness of panel. Effect of variation of various vertical and transverse shear modulus of elastic foundation on natural frequencies of free vibration, contact force history and transverse displacement of panel in low-velocity impact analysis is discussed and is compared with the available results in literature. https://mej.aut.ac.ir/article_318_432aca3a1e345e339f35a30c8f65edce.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Investigating Transverse Vibrations of Free-Free Beam on the Frictional Substrate and Validation with Test ResultsInvestigating Transverse Vibrations of Free-Free Beam on the Frictional Substrate and Validation with Test Results435131910.22060/mej.2013.319FAR. D. FirouzabadiMobinKavyanpoorJournal Article20140619In the present paper, the transverse vibrations of the Euler–Bernoulli beam along with the strong dry friction at the boundary conditions have been investigated. With special attention to the force of frictionon theboundary conditions which plays a role as one non-linear factor and brings out nonlinear response, natural frequencies also change despite the linear systems and these natural frequencies become a function of the force of friction and the force of friction in substrates is also a function of other parameters. The calculation of the beam frequencies as well as proper modeling of boundary conditions have been interesting for researchers and scientists. In the present study, the force of friction at substrates is investigated through the friction force modeling by using the nonlinear elastic-plastic Valanis model and also by the Classical Model of Coulomb friction. The assumed modes method for solving is used and the resulting equations by using the Fourth Runge-Kutta numerical method are solved. These two models are compared and the results of modal testing are used for the validation. Finally, according to Valanis parameters, it is shown that this model has a positive relation with the findings. The hardening effect of the frequency response-curves is also observed.In the present paper, the transverse vibrations of the Euler–Bernoulli beam along with the strong dry friction at the boundary conditions have been investigated. With special attention to the force of frictionon theboundary conditions which plays a role as one non-linear factor and brings out nonlinear response, natural frequencies also change despite the linear systems and these natural frequencies become a function of the force of friction and the force of friction in substrates is also a function of other parameters. The calculation of the beam frequencies as well as proper modeling of boundary conditions have been interesting for researchers and scientists. In the present study, the force of friction at substrates is investigated through the friction force modeling by using the nonlinear elastic-plastic Valanis model and also by the Classical Model of Coulomb friction. The assumed modes method for solving is used and the resulting equations by using the Fourth Runge-Kutta numerical method are solved. These two models are compared and the results of modal testing are used for the validation. Finally, according to Valanis parameters, it is shown that this model has a positive relation with the findings. The hardening effect of the frequency response-curves is also observed.https://mej.aut.ac.ir/article_319_8d3bba7425e7c98c50f52ca1b52d3735.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Modeling and Analysis of in Line and Cross Flow Vibration of Risers in Drill ShipsModeling and Analysis of in Line and Cross Flow Vibration of Risers in Drill Ships536232010.22060/mej.2013.320FAAmirMoghisehAbbasRahiHoumayonRiahiJournal Article20140619In the last few years, drilling activities took place in water depths of more than 3000m. In order to convey the hydrocarbon to the sea level and do drilling operations, a steal pipe is installed between the wellhead in the seabed and drill ships. A control system keeps the drill ship in a safe area above the wellhead. Since the diameter of the riser is much less than its length, it can be simplified into the beam model. The fluid dynamic forces are expressed in Morison formula by using short wave theory. It is assumed that the riser is connected to the drill ship by means of a heave compensator. This device provides a large static tensile force at the top of the riser. In addition, it reduces the longitudinal stress variation induced by the relative vertical motion of the drill ship and the riser. With these assumptions, the equations of motion governing the transverse displacement of the riser in two directions are obtained. These equations are solved by using the finite difference method and Runga-Kutta method. At the end, the effects of environmental and mechanical parameters on the dynamic behavior of the riser are discussed. In the last few years, drilling activities took place in water depths of more than 3000m. In order to convey the hydrocarbon to the sea level and do drilling operations, a steal pipe is installed between the wellhead in the seabed and drill ships. A control system keeps the drill ship in a safe area above the wellhead. Since the diameter of the riser is much less than its length, it can be simplified into the beam model. The fluid dynamic forces are expressed in Morison formula by using short wave theory. It is assumed that the riser is connected to the drill ship by means of a heave compensator. This device provides a large static tensile force at the top of the riser. In addition, it reduces the longitudinal stress variation induced by the relative vertical motion of the drill ship and the riser. With these assumptions, the equations of motion governing the transverse displacement of the riser in two directions are obtained. These equations are solved by using the finite difference method and Runga-Kutta method. At the end, the effects of environmental and mechanical parameters on the dynamic behavior of the riser are discussed. https://mej.aut.ac.ir/article_320_320722549d1751cf3f247855f937b982.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Extended Multiple Impedance Control of a Space Robot with Flexible MembersExtended Multiple Impedance Control of a Space Robot with Flexible Members637532110.22060/mej.2013.321FAPayamZarafshanS. A. A.MoosavianJournal Article20140619Dynamics and control of a space robotic system with flexible members during an object manipulation task is studied here. Flexible members such as solar panels of space free flying robotic systems and their flexible joints during a manoeuvre may get stimulated and vibrate. Therefore, such vibrations will cause some oscillatory disturbance forces on the moving base and manipulated object, which in turn produces error in the position and speed of the manipulating end-effectors. In this paper, considering a multiple arm space robotic system with flexible joints and flexible solar panels, the system dynamics is partitioned into two rigid and flexible bodies’ motion, and a concise model for control implementations of compounded rigid-flexible multi-body systems is developed. Then, based on a designated path/trajectory for a space robotic system, the multiple impedance control is extended to perform an object manipulation task by such complicated rigid-flexible multi-body systems. Finally, a space free flying robotic system is simulated which contains two manipulators with flexible joints, and a rotating antenna and a camera as its third and fourth arms, appended with two flexible solar panels. Obtained results reveal the merits of the proposed controller to successfully perform the manipulation task and effectively suppress the vibration of flexible elements.Dynamics and control of a space robotic system with flexible members during an object manipulation task is studied here. Flexible members such as solar panels of space free flying robotic systems and their flexible joints during a manoeuvre may get stimulated and vibrate. Therefore, such vibrations will cause some oscillatory disturbance forces on the moving base and manipulated object, which in turn produces error in the position and speed of the manipulating end-effectors. In this paper, considering a multiple arm space robotic system with flexible joints and flexible solar panels, the system dynamics is partitioned into two rigid and flexible bodies’ motion, and a concise model for control implementations of compounded rigid-flexible multi-body systems is developed. Then, based on a designated path/trajectory for a space robotic system, the multiple impedance control is extended to perform an object manipulation task by such complicated rigid-flexible multi-body systems. Finally, a space free flying robotic system is simulated which contains two manipulators with flexible joints, and a rotating antenna and a camera as its third and fourth arms, appended with two flexible solar panels. Obtained results reveal the merits of the proposed controller to successfully perform the manipulation task and effectively suppress the vibration of flexible elements.https://mej.aut.ac.ir/article_321_caf1a3dfb505ffed0d024130f58c5cfa.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Robust Adaptive Backstepping Control of a Nonlinear System with Uncertainty, Disturbance and Unknown Time DelayRobust Adaptive Backstepping Control of a Nonlinear System with Uncertainty, Disturbance and Unknown Time Delay778632210.22060/mej.2013.322FAHoseynChehardoliMohammadEghtesadJournal Article20140619In this paper, robust adaptive control is presented for a class of nonlinear systems in strict feedback form with uncertain time delay. It is assumed that time delay is not known, thus terms having delays must not appear in adaptation and control laws. By using the Lyapunov-Krasovskii functional, terms having time delay are deleted from adaptation and control laws. The adaptive backstepping method is used to design a controller and it is shown that this controller guarantees global uniform asymptotic stability of the system. A controller is robust against uncertain time delay and bounded disturbances, which enter the system. Two simulation results are provided to show the effectiveness of the proposed approach.In this paper, robust adaptive control is presented for a class of nonlinear systems in strict feedback form with uncertain time delay. It is assumed that time delay is not known, thus terms having delays must not appear in adaptation and control laws. By using the Lyapunov-Krasovskii functional, terms having time delay are deleted from adaptation and control laws. The adaptive backstepping method is used to design a controller and it is shown that this controller guarantees global uniform asymptotic stability of the system. A controller is robust against uncertain time delay and bounded disturbances, which enter the system. Two simulation results are provided to show the effectiveness of the proposed approach.https://mej.aut.ac.ir/article_322_5737c6ec2e0716f3d8a7a5c4e0de0d9a.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Survey, Experiment and Improvement of Micro Actuator Positioning for Precise Grinding by Neural NetworkSurvey, Experiment and Improvement of Micro Actuator Positioning for Precise Grinding by Neural Network8710432310.22060/mej.2013.323FAMohammadFazliS. M.RrezaeiMohammadZareienejadJournal Article20140619Precise grinding of fine shaped pieces with various arithmetic needs micro positioning and rapid movement of a work piece. Moreover, with regard to dressing of super abrasive grinding wheels, precise positioning of a dresser on the grinding wheel for achieving desired depth is needed. Piezoelectric actuators are convenient for micro positioning systems. Inherent hysteresis is one of the drawbacks in the use of these actuators. Neural networks can be used for this modeling. Ignoring the force can increase the positioning error remarkably. In this paper, the neural network is used for hysteresis modeling with attention to the important effect of loaded force. After modeling, the inverse hysteresis model is used as a compensator in a feed forward way to linearize the input-output relationship. Then using a PID closed loop controller and selecting a suitable coefficient for it, the maximum error was decreased to less than 2 percent of the working amplitude.Precise grinding of fine shaped pieces with various arithmetic needs micro positioning and rapid movement of a work piece. Moreover, with regard to dressing of super abrasive grinding wheels, precise positioning of a dresser on the grinding wheel for achieving desired depth is needed. Piezoelectric actuators are convenient for micro positioning systems. Inherent hysteresis is one of the drawbacks in the use of these actuators. Neural networks can be used for this modeling. Ignoring the force can increase the positioning error remarkably. In this paper, the neural network is used for hysteresis modeling with attention to the important effect of loaded force. After modeling, the inverse hysteresis model is used as a compensator in a feed forward way to linearize the input-output relationship. Then using a PID closed loop controller and selecting a suitable coefficient for it, the maximum error was decreased to less than 2 percent of the working amplitude.https://mej.aut.ac.ir/article_323_bc6dc48b743dc5d013b1abaebd2faed2.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Implementation of Neuro– Fuzzy and Multi-Layer Perceptron System Intelligent Techniques for Main Fault Diagnosis of Rotating MachineryImplementation of Neuro– Fuzzy and Multi-Layer Perceptron System Intelligent Techniques for Main Fault Diagnosis of Rotating Machinery10511832410.22060/mej.2013.324FAMajidKamariG.PayeganehM. N.KhajaviJournal Article20140619Nowadays, Fault detection of rotating machinery by diagnosing sings of starting point and growth of defect using intelligent techniques, discovering the defected parts and the reason behind them and prediction of remaining working life of the machine play an important role in preserve the machine from severe defects and the high price of repairing it. The goal of this paper is using the Adaptive Neural - Fuzzy Inference Systems (ANFIS) and Multi-Layer Perceptron (MLP)for detecting the original defects in rotating machinesincluding unbalancing, Bearing defects, Looseness and misalignment. So,in this study addition to the creation of this mechanism for automatic fault diagnosis, improve accuracy and speed of the network was also performed.Therefore, using the Principal Component Analysis (PCA), the input matrix was reduced to acceptable amontand the effectiveness of the ANFIS and MLP networks in detection of defects were compared with each other.To achieve this goal, mentioned networks were trained using feature vectors extracted from the spectrum frequency and waves.The obtained results showed that for 84 final measurements, the ANFIS and MLP networks have 91 and 78 averages percent successful in detecting the defects, respectively. Nowadays, Fault detection of rotating machinery by diagnosing sings of starting point and growth of defect using intelligent techniques, discovering the defected parts and the reason behind them and prediction of remaining working life of the machine play an important role in preserve the machine from severe defects and the high price of repairing it. The goal of this paper is using the Adaptive Neural - Fuzzy Inference Systems (ANFIS) and Multi-Layer Perceptron (MLP)for detecting the original defects in rotating machinesincluding unbalancing, Bearing defects, Looseness and misalignment. So,in this study addition to the creation of this mechanism for automatic fault diagnosis, improve accuracy and speed of the network was also performed.Therefore, using the Principal Component Analysis (PCA), the input matrix was reduced to acceptable amontand the effectiveness of the ANFIS and MLP networks in detection of defects were compared with each other.To achieve this goal, mentioned networks were trained using feature vectors extracted from the spectrum frequency and waves.The obtained results showed that for 84 final measurements, the ANFIS and MLP networks have 91 and 78 averages percent successful in detecting the defects, respectively. https://mej.aut.ac.ir/article_324_f2fc990265c712c49d51a18a32b39f0c.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603245220131222Analysis of Residual Material and Machining Error on Straight and Corner Curved Paths in Roughing of WEDMAnalysis of Residual Material and Machining Error on Straight and Corner Curved Paths in Roughing of WEDM11913732510.22060/mej.2013.325FAH. A.FirouzabadiJamshidParvizianAmirAbdullahAlirezaFadaei TehraniJournal Article20140619Wire electrical discharge machining (wire-EDM) is able to generate delicate and complex shapes on hard materials which are difficult to cut. Inaccuracy in the cutting of small radius curved corners is one of the major problems in this process. In the present paper, corner radii machining errors have been investigated. Experiments are designed using the Full Factorial Method for roughing operations by considering frequency of discharges, wire tension and radius of curvature as variables, and the residual material on straight and curved paths as the output parameters. Practical works are implemented on tool steel 1.2510. By employing statistical techniques for analysis and by calculating variable side gap on curved corners, the machining error is obtained for 150, 300 and 450 µm radius curvatures. Results show that the thickness of residual material left on the workpiece on straight and curved paths can be the same if the cutting path on curvature is corrected according to the findings of this paper.Wire electrical discharge machining (wire-EDM) is able to generate delicate and complex shapes on hard materials which are difficult to cut. Inaccuracy in the cutting of small radius curved corners is one of the major problems in this process. In the present paper, corner radii machining errors have been investigated. Experiments are designed using the Full Factorial Method for roughing operations by considering frequency of discharges, wire tension and radius of curvature as variables, and the residual material on straight and curved paths as the output parameters. Practical works are implemented on tool steel 1.2510. By employing statistical techniques for analysis and by calculating variable side gap on curved corners, the machining error is obtained for 150, 300 and 450 µm radius curvatures. Results show that the thickness of residual material left on the workpiece on straight and curved paths can be the same if the cutting path on curvature is corrected according to the findings of this paper.https://mej.aut.ac.ir/article_325_89f0fd5c927d466d6ec9a21b9ac34ffa.pdf