Amirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603255220230421Investigating the effect of thermal cycles on the recovery of tensile strength in self-healing composites under impact loadingInvestigating the effect of thermal cycles on the recovery of tensile strength in self-healing composites under impact loading159178509010.22060/mej.2023.21725.7496FAAliTalezadehlariDepartment of Mechanical Engineering, University of Larestan, Lar, IranAliNikbakhtNew Technologies Research Center (NTRC), Amirkabir University of Technology, Tehran, IranJournal Article20220824<span style="letter-spacing: .05pt;">Here the healing process of glass/epoxy composites is studied experimentally. The healing agent is composed of ML506 epoxy resin and HA-11 hardener which is charged into microtubes. The microtubes are interleaved between the first and the second and the fifth and the sixth layers. The initial damage is introduced to the samples by drop weight impact tests and the recovery percentage of the tensile strength due to healing process is measured by tensile test. The effects of healing time (without thermal cycles), number of healing units and thermal cycles are investigated on the recovery of the tensile strength. Composite samples containing 8, 16 and 32 healing units are studied in the periods of 1, 6 and 12 days after the initial damage. Also, some damaged samples are set to 1, 3, 5 and 7 thermal cycles and after one day, tensile tests are carried out. The results show that without thermal cycles the healing process is almost completed after 6 days with an 83% recovery. In addition, the maximum amount of tensile strength recovery is equal to 86% which is related to the samples with 32 healing units after 12 days. This amount of healing efficiency can also be achieved by means of 5 thermal cycles. This is also true for thermal cycles where the effect of thermal cycles is tangible up to 5 cycles.</span><span style="letter-spacing: .05pt;">Here the healing process of glass/epoxy composites is studied experimentally. The healing agent is composed of ML506 epoxy resin and HA-11 hardener which is charged into microtubes. The microtubes are interleaved between the first and the second and the fifth and the sixth layers. The initial damage is introduced to the samples by drop weight impact tests and the recovery percentage of the tensile strength due to healing process is measured by tensile test. The effects of healing time (without thermal cycles), number of healing units and thermal cycles are investigated on the recovery of the tensile strength. Composite samples containing 8, 16 and 32 healing units are studied in the periods of 1, 6 and 12 days after the initial damage. Also, some damaged samples are set to 1, 3, 5 and 7 thermal cycles and after one day, tensile tests are carried out. The results show that without thermal cycles the healing process is almost completed after 6 days with an 83% recovery. In addition, the maximum amount of tensile strength recovery is equal to 86% which is related to the samples with 32 healing units after 12 days. This amount of healing efficiency can also be achieved by means of 5 thermal cycles. This is also true for thermal cycles where the effect of thermal cycles is tangible up to 5 cycles.</span>https://mej.aut.ac.ir/article_5090_98c56bce74669e2e4e7a9fc1caa8c326.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603255220230421Design and analysis of mechanical behavior of a novel lattice auxetic structure based on rigid rotating mechanismDesign and analysis of mechanical behavior of a novel lattice auxetic structure based on rigid rotating mechanism179192509610.22060/mej.2023.21749.7506FARezaJafari NedoushanDepartment of Mechanical Engineering, Isfahan University of Technology,, Isfahan, IranMohammad JavadAbgharyDepartment of Textile Engineering, Yazd University, Yazd, IranJournal Article20220906Auxetic materials with negative Poisson’s ratio, as a group of metamaterials, attracted significant attentions among researchers due to their interesting and remarkable mechanical properties. Rigid rotating structures are a subcategory of auxetic materials which can show the same behavior in various directions by tuning their parameters, but due to using rigid rotating blocks their relative density is high. As the rotating blocks are connected by weak joints, stiffness and strength of these structures are low and considering high relative density of these structures specific mechanical properties are even in worse condition. In this research, novel lattice structures based on rigid rotating structures but with remarkably lower relative density were presented. To reduce relative density of these structures, bar elements were used instead of rigid blocks. 3D printing method was used to manufacture samples with these structures and then tensile test was performed on the samples. Poisson’s ratios of the samples were measured by recording image of the structures before and during deformation. The behavior of the structures was predicted by finite element method and compared with experimental measurements. Both of the methods showed auxetic behavior of the structures. Then deformation mechanism of the structures and the effect of the structures shape on the auxeticity were investigated.Auxetic materials with negative Poisson’s ratio, as a group of metamaterials, attracted significant attentions among researchers due to their interesting and remarkable mechanical properties. Rigid rotating structures are a subcategory of auxetic materials which can show the same behavior in various directions by tuning their parameters, but due to using rigid rotating blocks their relative density is high. As the rotating blocks are connected by weak joints, stiffness and strength of these structures are low and considering high relative density of these structures specific mechanical properties are even in worse condition. In this research, novel lattice structures based on rigid rotating structures but with remarkably lower relative density were presented. To reduce relative density of these structures, bar elements were used instead of rigid blocks. 3D printing method was used to manufacture samples with these structures and then tensile test was performed on the samples. Poisson’s ratios of the samples were measured by recording image of the structures before and during deformation. The behavior of the structures was predicted by finite element method and compared with experimental measurements. Both of the methods showed auxetic behavior of the structures. Then deformation mechanism of the structures and the effect of the structures shape on the auxeticity were investigated.https://mej.aut.ac.ir/article_5096_90fd4f88f588ae64038134f1eeaa023f.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603255220230421Modeling and Nonlinear vibration analysis of Euler-Bernoulli beam under finite deformationModeling and Nonlinear vibration analysis of Euler-Bernoulli beam under finite deformation193212510010.22060/mej.2023.21645.7484FAMohammad MasabDoralizadehDepartment of Mechanical Engineering, Yazd University, Yazd, IranAli RezaFotouhiDepartment of Mechanical Engineering, Yazd University, Yazd, IranMostafaGhayourDepartment of Mechanical Engineering, Isfahan University of Technology, Isfahan, IranJournal Article20220730According to the wide presence of beams in engineering structures, it is very useful to understand how the beams vibrate nonlinearly in conditions where they oscillate with a large amplitude. In this paper, the nonlinear vibrations of an Euler-Bernoulli beam under finite deformation are investigated. In this study, unlike other papers, in order to obtain the governing equations of the beam, the field-displacement relationship has been done without approximation. Based on this, the strain-displacement relations are calculated using the Green Lagrange strain, and the nonlinear form of the equations is obtained by using the Hamilton method. In order to solve the partial differential equation, using the Galerkin method, the equation has been converted to an ordinary differential equation and finally solved using the multiple scale method and compared with the Rung-Kutta numerical method. To evaluate the accuracy of the method and the validity of the modelling, the obtained results are compared with the Euler–Bernoulli beam theory and the Von-Karman nonlinear model. The results show that the present method in low vibration amplitudes is consistent with the model of Euler-Bernoulli and Von-Karman, but with increasing amplitude of oscillations, the results of these models will be significantly different from each other, which is as expected.According to the wide presence of beams in engineering structures, it is very useful to understand how the beams vibrate nonlinearly in conditions where they oscillate with a large amplitude. In this paper, the nonlinear vibrations of an Euler-Bernoulli beam under finite deformation are investigated. In this study, unlike other papers, in order to obtain the governing equations of the beam, the field-displacement relationship has been done without approximation. Based on this, the strain-displacement relations are calculated using the Green Lagrange strain, and the nonlinear form of the equations is obtained by using the Hamilton method. In order to solve the partial differential equation, using the Galerkin method, the equation has been converted to an ordinary differential equation and finally solved using the multiple scale method and compared with the Rung-Kutta numerical method. To evaluate the accuracy of the method and the validity of the modelling, the obtained results are compared with the Euler–Bernoulli beam theory and the Von-Karman nonlinear model. The results show that the present method in low vibration amplitudes is consistent with the model of Euler-Bernoulli and Von-Karman, but with increasing amplitude of oscillations, the results of these models will be significantly different from each other, which is as expected.https://mej.aut.ac.ir/article_5100_91bc333f6967019ac47b49ca0f2fa757.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603255220230421State-space approach for bending analysis of functionally graded piezoelectric plate using five-variable refined plate theoryState-space approach for bending analysis of functionally graded piezoelectric plate using five-variable refined plate theory213234510310.22060/mej.2023.21600.7476FANiloufarSalmanpourDepartment of Mechanical Engineering, Shiraz University of Technology, Shiraz, IranSeyed JafarRouzegarDepartment of Mechanical Engineering, Shiraz University of Technology, Shiraz, IranJournal Article20220715In this paper, an analytical solution for bending analysis of functionally-graded piezoelectric plate with two simply-supported parallel edges and two other arbitrary boundary conditions under uniformly-distributed transverse loading is presented. The five-variable refined plate theory is employed for describing the displacement field. This theory, despite the few numbers of unknown variables, predicts a parabolic distribution for transverse shear stresses across the thickness and also considers the thickness-stretching effect. The governing equations are obtained using Hamilton’s principle and Maxwell's equation. The Levy-type solution in conjunction with the state-space approach is used to solve them. Comparing the results with those obtained by the higher-order shear theories and Abaqus finite element simulation confirms the accuracy and efficiency of the proposed method. It can be seen that for the length-to-thickness ratio of 10 and the power-law index of 0.5, the value of non-dimensional deflection of the plate with the clamped boundary condition is 0.3327, which has the largest amount of stiffness, while the value of the non-dimensional deflection of the plate with two parallel free boundary condition edges having the lowest amount of stiffness is 2.2036. In addition, for the plate with a clamped boundary condition and length-to-thickness ratio of 10, with the increase of the power index from 0.5 to 10, the value of displacement changes from 0.3327 to 0.3545, which means an increase of about 6%.In this paper, an analytical solution for bending analysis of functionally-graded piezoelectric plate with two simply-supported parallel edges and two other arbitrary boundary conditions under uniformly-distributed transverse loading is presented. The five-variable refined plate theory is employed for describing the displacement field. This theory, despite the few numbers of unknown variables, predicts a parabolic distribution for transverse shear stresses across the thickness and also considers the thickness-stretching effect. The governing equations are obtained using Hamilton’s principle and Maxwell's equation. The Levy-type solution in conjunction with the state-space approach is used to solve them. Comparing the results with those obtained by the higher-order shear theories and Abaqus finite element simulation confirms the accuracy and efficiency of the proposed method. It can be seen that for the length-to-thickness ratio of 10 and the power-law index of 0.5, the value of non-dimensional deflection of the plate with the clamped boundary condition is 0.3327, which has the largest amount of stiffness, while the value of the non-dimensional deflection of the plate with two parallel free boundary condition edges having the lowest amount of stiffness is 2.2036. In addition, for the plate with a clamped boundary condition and length-to-thickness ratio of 10, with the increase of the power index from 0.5 to 10, the value of displacement changes from 0.3327 to 0.3545, which means an increase of about 6%.https://mej.aut.ac.ir/article_5103_03a3655fff3e9bdea48de9f49e938e32.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603255220230421Aeroelastic analysis of a thin composite plate, with the effect of general and local geometric defectsAeroelastic analysis of a thin composite plate, with the effect of general and local geometric defects235256512310.22060/mej.2023.21270.7413FAHamidMoosazadehtarbiat modares univercity of technologyMohammad MahdiMohammadiFaculty of Mechanic - Malek Ashtar University of Technology- Tehran- Iran0000-0003-4384-6674Journal Article20220405In this study, the effect of laminate type and number of layers, fiber angle and modulus of elasticity in combination with the effect of global and local geometric defects has been investigated as a new combination in the field of aeroelasticity. Using the principle of virtual work, by directly integrating the problem-solving boundary, the governing equations are determined based on Kirchhoff thin-plate theory. Then, using the assumption mode method in Galerkin's theory, the partial differential equations are converted to ordinary nonlinear differential equations. The final nonlinear equations are solved using the Runge–Kutta numerical method and the time domain results are extracted to determine the flutter and post-flutter behavior of the plate. The results of the analysis showed that the geometric defect with non-uniform and asymmetric load production, the type of layering, the number of layers and mechanical loads are effective on the plane flutter boundary. The effect of local geometric defects in determining the flutter border is not necessarily destabilizing, but in some cases, depending on the size and location of the defect, it is also possible to increase the stability of the plane flutter boundary. In addition, the dynamic behavior of the plate under the effect of local geometric defects with different shapes and dimensions is very diverse and different from the of general defect (first mode shape) or shell with small curvature.In this study, the effect of laminate type and number of layers, fiber angle and modulus of elasticity in combination with the effect of global and local geometric defects has been investigated as a new combination in the field of aeroelasticity. Using the principle of virtual work, by directly integrating the problem-solving boundary, the governing equations are determined based on Kirchhoff thin-plate theory. Then, using the assumption mode method in Galerkin's theory, the partial differential equations are converted to ordinary nonlinear differential equations. The final nonlinear equations are solved using the Runge–Kutta numerical method and the time domain results are extracted to determine the flutter and post-flutter behavior of the plate. The results of the analysis showed that the geometric defect with non-uniform and asymmetric load production, the type of layering, the number of layers and mechanical loads are effective on the plane flutter boundary. The effect of local geometric defects in determining the flutter border is not necessarily destabilizing, but in some cases, depending on the size and location of the defect, it is also possible to increase the stability of the plane flutter boundary. In addition, the dynamic behavior of the plate under the effect of local geometric defects with different shapes and dimensions is very diverse and different from the of general defect (first mode shape) or shell with small curvature.https://mej.aut.ac.ir/article_5123_037a595e6f4f0576a9efe43154d71c18.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603255220230421A Practical Method for Controlling the Parallel Robot Path Based on the Sliding Mode Method with Fuzzy Adjustable CoefficientsA Practical Method for Controlling the Parallel Robot Path Based on the Sliding Mode Method with Fuzzy Adjustable Coefficients257282513410.22060/mej.2023.21694.7491FABabakTaranTarbiat Modarres UniversityMostafaBarghandanUniversity of ZanjanAli AkbarPirmohammadiMechanical Engineering, Zanjan University, Zanjan
https://orcid.org/0000-0001-5070-14950000-0001-5070-1495SalehMobayenUniversity of Zanjan, Zanjan, IranJournal Article20220822Parallel manipulators are of interest in various industries due to their high precision, rigidity, high speed and low inertia. Controlling these types of systems faces challenges due to their complex and non-linear dynamics. Among the many methods of controlling the path of parallel manipulators, computed torque and sliding mode methods are the famous methods that are proposed. In practical applications, when the speed of the robot increases, adjusting the controller parameters is very difficult and depends on the working conditions of the robot, so the robot cannot work properly with fixed and predetermined coefficients under any condition. The type of path, the speed of the robot along the path, the initial conditions of the end effector of the robot in relation to the path, and even the sampling time are factors that affect the accuracy of the controller, and by changing each of them, it may be necessary to redefine the parameters of the control system and change the control coefficients. In this article, a method is presented which is based on the sliding mode method and the coefficients of the control system are adjusted appropriately by changing the sliding surface and sliding speed using the fuzzy method. The performance of this method has been investigated in two ways: modeling in MATLAB software and real time applying it to a planar parallel robot.Parallel manipulators are of interest in various industries due to their high precision, rigidity, high speed and low inertia. Controlling these types of systems faces challenges due to their complex and non-linear dynamics. Among the many methods of controlling the path of parallel manipulators, computed torque and sliding mode methods are the famous methods that are proposed. In practical applications, when the speed of the robot increases, adjusting the controller parameters is very difficult and depends on the working conditions of the robot, so the robot cannot work properly with fixed and predetermined coefficients under any condition. The type of path, the speed of the robot along the path, the initial conditions of the end effector of the robot in relation to the path, and even the sampling time are factors that affect the accuracy of the controller, and by changing each of them, it may be necessary to redefine the parameters of the control system and change the control coefficients. In this article, a method is presented which is based on the sliding mode method and the coefficients of the control system are adjusted appropriately by changing the sliding surface and sliding speed using the fuzzy method. The performance of this method has been investigated in two ways: modeling in MATLAB software and real time applying it to a planar parallel robot.https://mej.aut.ac.ir/article_5134_cceff8faa855336ad53b3325914caea2.pdf