Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 An Experimental Approach for Determination of Locators Reaction Forces in Milling Fixtures An Experimental Approach for Determination of Locators Reaction Forces in Milling Fixtures 5615 5626 4545 10.22060/mej.2021.19596.7065 FA Mahfooz Sohrabifard Advanced Technologies in Machine Tools Lab, Mechanical Engineering Faculty, Tarbiat Modares University, Tehran, Iran Mohamad Javad Nategh Mechanical Engineering Faculty, Tarbiat Modares University Journal Article 2021 02 08 The contact stiffness between the workpiece and fixture locating system is one of the decisive factors for the maintenance of the stability of the workpiece during the machining process. In order to estimate the contact stiffness, it is needed to determine the locator reaction forces. These forces are created by the clamping forces, cutting forces, workpiece weight, and friction effects of the contact between the workpiece and fixture locating system. Some analytical approaches have already been presented for calculating the location reaction forces. However, there are six equations for a 3-2-1 locating system, but 18 unknown parameters. Therefore, an optimization solution is proposed in the literature to obtain the reaction forces which involves several simplifying assumptions which result in considerable errors in the solution. In this study, in addition to presenting the mathematical model of the total system, an experimental approach has been proposed in order to determine the locator reaction forces. This can provide a suitable means for evaluating the optimization solutions and analytical models for determining the locator reaction forces and contact stiffness and diminishing the errors. The contact stiffness between the workpiece and fixture locating system is one of the decisive factors for the maintenance of the stability of the workpiece during the machining process. In order to estimate the contact stiffness, it is needed to determine the locator reaction forces. These forces are created by the clamping forces, cutting forces, workpiece weight, and friction effects of the contact between the workpiece and fixture locating system. Some analytical approaches have already been presented for calculating the location reaction forces. However, there are six equations for a 3-2-1 locating system, but 18 unknown parameters. Therefore, an optimization solution is proposed in the literature to obtain the reaction forces which involves several simplifying assumptions which result in considerable errors in the solution. In this study, in addition to presenting the mathematical model of the total system, an experimental approach has been proposed in order to determine the locator reaction forces. This can provide a suitable means for evaluating the optimization solutions and analytical models for determining the locator reaction forces and contact stiffness and diminishing the errors.

https://mej.aut.ac.ir/article_4545_1f6419b1cbe79c71410cb320fc094775.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Experimental Study of the Effect of Initial Surface Roughness on Ball Burnishing Forces and Endurance Limit of AISI 4130 Hardened Steel Experimental Study of the Effect of Initial Surface Roughness on Ball Burnishing Forces and Endurance Limit of AISI 4130 Hardened Steel 5627 5644 4503 10.22060/mej.2021.19853.7131 FA Moosa Arsalani Ph.D. Student, Mechanical Engineering Department, Amirkabir University of Technology, Theran, Iran. Mohammad Reza Razfar Full Professor, Mechanical Engineering Department, Amirkabir University of Technology,Tehran, Iran. Amir Abdullah Associate Professor, Mechanical Engineering Department, Amirkabir University of Technology, Tehran, Iran. Mohsen Khajehzadeh Mechanical Engineering Department of Amirkabir University of Technology Journal Article 2021 04 11 Machining of hardened steels, which their hardness is generally higher than 45 Rockwell C, is called hard turning. These components usually work under dynamic loading conditions and require a high level of surface finish (in the order of 0.15 μm Ra) which cannot be achieved by sequential hard turning and burnishing processes. However, there are serious concerns about this complement grinding operation; the grinding process, on one hand, increases tensile residual stresses and on the other hand, increases crack nucleation regions. Therefore, these two factors might decrease workpiece fatigue strength. So, in this paper, the effects of adding a grinding operation before the ball burnishing process, have been experimentally studied on final surface roughness and burnishing forces; at the same time, in order to consider the possible destructive effects of the grinding process, a set of experimental measurements including surface residual stresses and endurance limit measurement, have been done for AISI 4130 fatigue samples. Based on the achieved results, adding a grinding operation before the burnishing process has led to a 91.56% improvement in surface finish and a 39.52% reduction in burnishing forces. In addition, surface residual stress is compressive and there is a slight difference in the magnitude of compressive residual stresses in comparison to burnished hard turned samples. Due to these positive findings, the endurance limit of produced samples shows 10.95% improvement in comparison to burnished hard turned samples. Machining of hardened steels, which their hardness is generally higher than 45 Rockwell C, is called hard turning. These components usually work under dynamic loading conditions and require a high level of surface finish (in the order of 0.15 μm Ra) which cannot be achieved by sequential hard turning and burnishing processes. However, there are serious concerns about this complement grinding operation; the grinding process, on one hand, increases tensile residual stresses and on the other hand, increases crack nucleation regions. Therefore, these two factors might decrease workpiece fatigue strength. So, in this paper, the effects of adding a grinding operation before the ball burnishing process, have been experimentally studied on final surface roughness and burnishing forces; at the same time, in order to consider the possible destructive effects of the grinding process, a set of experimental measurements including surface residual stresses and endurance limit measurement, have been done for AISI 4130 fatigue samples. Based on the achieved results, adding a grinding operation before the burnishing process has led to a 91.56% improvement in surface finish and a 39.52% reduction in burnishing forces. In addition, surface residual stress is compressive and there is a slight difference in the magnitude of compressive residual stresses in comparison to burnished hard turned samples. Due to these positive findings, the endurance limit of produced samples shows 10.95% improvement in comparison to burnished hard turned samples.

https://mej.aut.ac.ir/article_4503_09a69de15cf89bc7fe8c0642f906a4dd.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Effect of 3D-Printing and Compression Molding on Anisotropy of Acrylonitrile Butadiene Styrene Micro Specimen: A Comparative Study Based on Digital Image Correlation Effect of 3D-Printing and Compression Molding on Anisotropy of Acrylonitrile Butadiene Styrene Micro Specimen: A Comparative Study Based on Digital Image Correlation 5645 5658 4522 10.22060/mej.2021.19874.7135 FA Sina Nazari-Onlaghi School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran Alireza Sadeghi School of Mechanical Engineering, College of Engineering, University of Tehran, Iran Morad KARIMPOUR School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran Hadi Mohammadi School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran Journal Article 2021 04 17 This paper aims to calculate and compare normal anisotropy coefficients in 3D-printed and hot-compression molded micro acrylonitrile butadiene styrene specimens. To achieve this goal, micro specimens of additively-printed and compression-molded acrylonitrile butadiene styrene were fabricated and tested using a micro-tensile testing apparatus integrated with an optical microscope while deformation of the specimens was recorded by a camera. Frames from this video were selected and strain distribution on a micron-sized area of interest was obtained using digital image correlation analysis. It was shown that there exists a close agreement between digital image correlation results and in situ optical observations. The plastic anisotropy coefficients (R-values) were then calculated from the surface strains as a function of the applied strain. For this purpose, a through-thickness strain component was obtained assuming plastic incompressibility condition. Results showed that both micro samples revealed an anisotropic response during plastic deformation. At low plastic strains, the printed micro specimen exhibits a more anisotropic behavior than the monolithic micro specimen. As the deformation proceeds, the normal anisotropy coefficient increases for the additively-manufactured micro specimen and decreases for the hot-pressed micro specimen. This paper aims to calculate and compare normal anisotropy coefficients in 3D-printed and hot-compression molded micro acrylonitrile butadiene styrene specimens. To achieve this goal, micro specimens of additively-printed and compression-molded acrylonitrile butadiene styrene were fabricated and tested using a micro-tensile testing apparatus integrated with an optical microscope while deformation of the specimens was recorded by a camera. Frames from this video were selected and strain distribution on a micron-sized area of interest was obtained using digital image correlation analysis. It was shown that there exists a close agreement between digital image correlation results and in situ optical observations. The plastic anisotropy coefficients (R-values) were then calculated from the surface strains as a function of the applied strain. For this purpose, a through-thickness strain component was obtained assuming plastic incompressibility condition. Results showed that both micro samples revealed an anisotropic response during plastic deformation. At low plastic strains, the printed micro specimen exhibits a more anisotropic behavior than the monolithic micro specimen. As the deformation proceeds, the normal anisotropy coefficient increases for the additively-manufactured micro specimen and decreases for the hot-pressed micro specimen.

https://mej.aut.ac.ir/article_4522_f110a326be6999afdeb8e7002c0ce44d.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Experimental Study of Effects of Hydrogen Embrittlement and Residual Stress on Mechanical Properties of GTD450 Experimental Study of Effects of Hydrogen Embrittlement and Residual Stress on Mechanical Properties of GTD450 5659 5678 4402 10.22060/mej.2021.19459.7032 FA Sepide Nosrati Department of mechanical engineering, Faculty of engineering, University of Zanjan, Zanjan, Iran Esmaeil Poursaeidi University Professor/ Department of mechanical engineering, Faculty of engineering, University of Zanjan, Zanjan, Iran. َAmin Dadashi PhD student/ Faculty of mechanical engineering, Tarbiat Modares University, Tehran, Iran Journal Article 2021 01 09 The subject of the present paper is the experimental study of the effects of hydrogen embrittlement with residual stress on the mechanical properties of GTD450 alloy. Hence, 0.5 M sulfuric acid was used to create one- and two-hour hydrogen charging, and the cylindrical-toothed method was used to generate residual stress. Based on experimental findings, changes in flexibility and percentage of reduction of failure area, compared to the baseline conditions ranged from 42.69% to 74.68% and 11.78% to 39.58%, respectively. The results of statistical analysis have estimated the contribution of residual stress and hydrogen embrittlement to flexibility as 1.15% and 67.05%, respectively. For the residual stress related to the five kN force, by increasing the hydrogen charging to two hours, the toughness value decreases by 60.54%. It was also observed that the maximum change in yield stress is 1.68%, which is caused in the sample by one-hour hydrogen embrittlement and residual stress due to a force of nine kN. In the baseline case, the necking was collapsed with high strain, and the area of failure was reduced by 36%; however, under two-hour charging, failure occurred with a minimum of necking, low strain, and slight reduction of failure area by 21.75%. The subject of the present paper is the experimental study of the effects of hydrogen embrittlement with residual stress on the mechanical properties of GTD450 alloy. Hence, 0.5 M sulfuric acid was used to create one- and two-hour hydrogen charging, and the cylindrical-toothed method was used to generate residual stress. Based on experimental findings, changes in flexibility and percentage of reduction of failure area, compared to the baseline conditions ranged from 42.69% to 74.68% and 11.78% to 39.58%, respectively. The results of statistical analysis have estimated the contribution of residual stress and hydrogen embrittlement to flexibility as 1.15% and 67.05%, respectively. For the residual stress related to the five kN force, by increasing the hydrogen charging to two hours, the toughness value decreases by 60.54%. It was also observed that the maximum change in yield stress is 1.68%, which is caused in the sample by one-hour hydrogen embrittlement and residual stress due to a force of nine kN. In the baseline case, the necking was collapsed with high strain, and the area of failure was reduced by 36%; however, under two-hour charging, failure occurred with a minimum of necking, low strain, and slight reduction of failure area by 21.75%.

https://mej.aut.ac.ir/article_4402_19485224d128528da1602ca47383f078.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Micromechanical Damage Model for Plasticity of ‎Metals to Predict Failure under Shear Loads Micromechanical Damage Model for Plasticity of ‎Metals to Predict Failure under Shear Loads 5679 5702 4526 10.22060/mej.2021.19546.7050 FA Hamed Ghoolipour Amirkanir University of Technology, Mechanical Engineering Department, Tehran, Iran FaridReza Biglari Kamran Nikbin Imperial College-مهندسی مکانیک Journal Article 2021 01 24 The present work deals with the Gurson-Tvergaard-Needleman micromechanics based damage model to add ‎the ability to predict damage under shear loads and use it in modeling damage and failure under shear dominated ‎loading conditions. In the development of the Gurson-Tvergaard-Needleman model, since different damages have ‎different physical concepts and attenuation effects, so an independent shear damage parameter was presented as a ‎function of an equivalent plastic strain of the matrix. The modified Gurson-Tvergaard-Needleman damage model ‎was implemented by developing a code in the Abaqus software. To use the modified Gurson-Tvergaard-‎Needleman model, 16 input parameters of the model were determined for the material under study. After ‎modifying the model, developing the code, and determining the input parameters, it was first tested on a single ‎element. The results of the developed model showed complete agreement with the results of the basic Gurson-‎Tvergaard-Needleman model and analytical solutions under tensile and shear loads, respectively. Finally, the ‎developed model was tested in shear loading on the shear specimen. It was observed that the modified model ‎eliminates the weakness of the base Gurson-Tvergaard-Needleman model and well predicts the occurrence of ‎damage and weakening of the mechanical properties of the material under the prevailing shear conditions.‎ The present work deals with the Gurson-Tvergaard-Needleman micromechanics based damage model to add ‎the ability to predict damage under shear loads and use it in modeling damage and failure under shear dominated ‎loading conditions. In the development of the Gurson-Tvergaard-Needleman model, since different damages have ‎different physical concepts and attenuation effects, so an independent shear damage parameter was presented as a ‎function of an equivalent plastic strain of the matrix. The modified Gurson-Tvergaard-Needleman damage model ‎was implemented by developing a code in the Abaqus software. To use the modified Gurson-Tvergaard-‎Needleman model, 16 input parameters of the model were determined for the material under study. After ‎modifying the model, developing the code, and determining the input parameters, it was first tested on a single ‎element. The results of the developed model showed complete agreement with the results of the basic Gurson-‎Tvergaard-Needleman model and analytical solutions under tensile and shear loads, respectively. Finally, the ‎developed model was tested in shear loading on the shear specimen. It was observed that the modified model ‎eliminates the weakness of the base Gurson-Tvergaard-Needleman model and well predicts the occurrence of ‎damage and weakening of the mechanical properties of the material under the prevailing shear conditions.‎

https://mej.aut.ac.ir/article_4526_1dfcb07c683107f038d8c886145d097e.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Numerical Simulation of Elastoplastic Behavior and Damage Evolution at Various Stress Triaxiality Numerical Simulation of Elastoplastic Behavior and Damage Evolution at Various Stress Triaxiality 5703 5724 4570 10.22060/mej.2021.19697.7090 FA Mahdi Ansari MSc, Mahdi Ansari, School of mechanical engineering, University of Tehran Seyed Mahdi Ganjiani 0000-0001-9839-7795 Amin Lalegani Dezakia MSc, School of mechanical engineering, University of Tehran Journal Article 2021 03 03 The theory of continuum damage mechanics with a phenomenological approach is able to simulate phenomena such as soft strain, local necking of materials, and their failure. Stress triaxiality is defined as the stress state in a material that strongly affects the ductile failure phenomena. In this study, two damage models, Ganjiani and Bonora, are chosen to simulate and compare the elastoplastic behavior as well as damage evolution of some metals. These damage models are sensitive to the stress triaxiality. In order to validate the capability of the models in structural response, the proposed model has been implemented into user-defined subroutines VUMAT in the finite element program ABAQUS/Explicit. For this purpose, the explicit stress integration algorithms of the model have been explained. The model has been validated by comparing the predicted results with experimental data. The simulations are performed for steel 1045, aluminum 2024-T351, and steel HY130. The details of the integration algorithm in the framework of the explicit scheme are presented. Also, the model is developed in the large strain deformation. For the determination of the constants in the models, the stress-strain, the damage-strain, and the fracture strain-triaxiality curves are used. The predicted curves of load-displacement from simulation have good agreement with corresponding experimental data. The theory of continuum damage mechanics with a phenomenological approach is able to simulate phenomena such as soft strain, local necking of materials, and their failure. Stress triaxiality is defined as the stress state in a material that strongly affects the ductile failure phenomena. In this study, two damage models, Ganjiani and Bonora, are chosen to simulate and compare the elastoplastic behavior as well as damage evolution of some metals. These damage models are sensitive to the stress triaxiality. In order to validate the capability of the models in structural response, the proposed model has been implemented into user-defined subroutines VUMAT in the finite element program ABAQUS/Explicit. For this purpose, the explicit stress integration algorithms of the model have been explained. The model has been validated by comparing the predicted results with experimental data. The simulations are performed for steel 1045, aluminum 2024-T351, and steel HY130. The details of the integration algorithm in the framework of the explicit scheme are presented. Also, the model is developed in the large strain deformation. For the determination of the constants in the models, the stress-strain, the damage-strain, and the fracture strain-triaxiality curves are used. The predicted curves of load-displacement from simulation have good agreement with corresponding experimental data.

https://mej.aut.ac.ir/article_4570_e9dae45ec08b498f7e1af247757c9b35.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 A Study on the Ballistic Behavior of Kevlar Fabric Impregnated with Shear Thickening Fluid Containing Graphene Oxide Additive A Study on the Ballistic Behavior of Kevlar Fabric Impregnated with Shear Thickening Fluid Containing Graphene Oxide Additive 5725 5738 4453 10.22060/mej.2021.19806.7119 FA Amirhosein Naghizadeh School of Mechanical Engineering, Iran University of Science and Technology (IUST), Tehran, Iran Hadi Khoramishad School of Mechanical Engineering, Iran University of Science and Technology 0000-0003-2705-0203 Maisam Jalaly Nanotechnology Department, School of Advanced Technologies, Iran University of Science &amp;amp; Technology (IUST), Tehran, Iran 0000-0002-3123-7460 Journal Article 2021 03 31 In this research, the effects of graphene oxide as an additive to Kevlar fabric impregnated with nanosilica/polyethylene glycol shear thickening fluid on the ballistic performance were investigated. In order to understand the influence of shear thickening fluid, pull-out tests were accomplished to assess the friction between yarns. The energy absorption in the high-impact ballistic test for the fabric impregnated with shear thickening fluid increased by 25.8% compared to that for the neat Kevlar fabric. This parameter for the fabric impregnated with shear thickening fluid-0.2 wt.% graphene oxide was 23.3% as compared with that of the neat fabric, demonstrating the deteriorating effect of graphene oxide additive. The results of the pull-up tests were in agreement with ballistic tests, meaning that the increase or decrease in the maximum forces in pull-up tests was followed by the increase or decrease in the energy absorption in ballistic tests. Compared to the sample impregnated with shear thickening fluid, adding graphene oxide causes the decrease in the maximum force in the pull-up test, resulting in a reduction in restriction of yarns movement, consequently facilitating their movement inside the fabric. In this research, the effects of graphene oxide as an additive to Kevlar fabric impregnated with nanosilica/polyethylene glycol shear thickening fluid on the ballistic performance were investigated. In order to understand the influence of shear thickening fluid, pull-out tests were accomplished to assess the friction between yarns. The energy absorption in the high-impact ballistic test for the fabric impregnated with shear thickening fluid increased by 25.8% compared to that for the neat Kevlar fabric. This parameter for the fabric impregnated with shear thickening fluid-0.2 wt.% graphene oxide was 23.3% as compared with that of the neat fabric, demonstrating the deteriorating effect of graphene oxide additive. The results of the pull-up tests were in agreement with ballistic tests, meaning that the increase or decrease in the maximum forces in pull-up tests was followed by the increase or decrease in the energy absorption in ballistic tests. Compared to the sample impregnated with shear thickening fluid, adding graphene oxide causes the decrease in the maximum force in the pull-up test, resulting in a reduction in restriction of yarns movement, consequently facilitating their movement inside the fabric.

https://mej.aut.ac.ir/article_4453_fd95ec8df5dbeea25aa8e6c808bad583.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Analytical Study on Effect of Loosening on Nonlinear Vibration Behavior of Bolted Joints Analytical Study on Effect of Loosening on Nonlinear Vibration Behavior of Bolted Joints 5739 5754 4549 10.22060/mej.2021.19852.7132 FA Abouzar Pirdayr Department of Mechanical Engineering –Shiraz Branch Islamic Azad University shiraz Iran 0000-0001-7440-5500 Mehrdad Mohammadi Department of Mechanical Engineering &ndash;Shiraz Branch Islamic Azad University shiraz Iran Mohammad Javad Kazemzadeh-Parsi Department of Mechanical Engineering –Shiraz Branch Islamic Azad University shiraz Iran 0000-0002-5942-2238 Majid Rajabi School of Mechanical Engineering - Iran University of Science And Technology 0000-0001-9511-4382 Journal Article 2021 04 14 Bolt connections often loosen under environmental loading conditions and system vibrations, which can lead to disaster risks during its operation. In this study, the nonlinear vibration behavior of an aluminum single-lap joint has been studied analytically and experimentally. Accordingly, considering the effects of nonlinear behavior at the bole joint, a nonlinear two-degree of freedom model for this type of connection is proposed. Then, in order to determine the unknown parameters of the proposed model, the vibrational and dynamic properties of this structure have been estimated using experimental modal analysis and model updating method. Finally, the effect of the amplitude of the excitation force and the preload force of the bolts on the dynamic behavior of these systems has been studied analytically. Examination of amplitude-frequency curves shows that reducing the preload force of the bolts reduces the natural frequency and also distorts the amplitude-frequency curve to the left side, which indicates the softening nonlinear behavior of the system with decreasing applied bolt preload force. In addition, the comparison of the theoretical and experimental natural frequencies shows that the proposed model predicts the vibrational characteristics of these systems with good accuracy, and using the proposed model can study the dynamic behavior of these systems for different parameters Bolt connections often loosen under environmental loading conditions and system vibrations, which can lead to disaster risks during its operation. In this study, the nonlinear vibration behavior of an aluminum single-lap joint has been studied analytically and experimentally. Accordingly, considering the effects of nonlinear behavior at the bole joint, a nonlinear two-degree of freedom model for this type of connection is proposed. Then, in order to determine the unknown parameters of the proposed model, the vibrational and dynamic properties of this structure have been estimated using experimental modal analysis and model updating method. Finally, the effect of the amplitude of the excitation force and the preload force of the bolts on the dynamic behavior of these systems has been studied analytically. Examination of amplitude-frequency curves shows that reducing the preload force of the bolts reduces the natural frequency and also distorts the amplitude-frequency curve to the left side, which indicates the softening nonlinear behavior of the system with decreasing applied bolt preload force. In addition, the comparison of the theoretical and experimental natural frequencies shows that the proposed model predicts the vibrational characteristics of these systems with good accuracy, and using the proposed model can study the dynamic behavior of these systems for different parameters

https://mej.aut.ac.ir/article_4549_3eb2f1a06667bfb9daba7f7effa0284b.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Crystal Plasticity Finite Element Study of Necking Behavior of Aluminum Alloy Sheet Subject to Thickness-Stress Crystal Plasticity Finite Element Study of Necking Behavior of Aluminum Alloy Sheet Subject to Thickness-Stress 5755 5768 4517 10.22060/mej.2021.19957.7146 FA Mohammadreza Kargar Daroonkolaee MSc Mech. Eng., Department of Mechanical Engineering and Mechatronics, Shahrood Univ. of Tech., Shahrood, Iran 0000-0002-1975-7287 Seyed Hadi Ghaderi صنعتی شاهرود-مهندسی مکانیک 0000-0003-1198-6795 Journal Article 2021 04 29 This paper investigates the effect of thickness stress on the formability of aluminum alloy metal sheets using crystal plasticity finite element analysis. A self-hardening behavior is considered for the slip systems. Further, for the prediction of necking initiation and growth, the maximum shear strain criterion is used for damage initiation and evolution. In order to implement the model in Abaqus finite element package, a VUMAT was developed based on the discretized equations and forward Euler integration scheme. After verification of the developed code, the parameters of the model were calibrated against the tensile test results. For simulating tensile test of 1 mm thick sheet, a representative volume of 3×1.5×0.5 mm3،was partitioned into 14790 grains through a python code in ABAQUS/CAE environment and then discretized using 50 μm tetrahedral linear elements. Using the experimental data available in the literature and considering appropriate texture for the simulation domain, the crystal orientations were assigned through Euler angles. Then, tensile tests were performed on the sample in the presence of the thickness pressure stress. The results show that application of the through thickness stress increases the strain corresponding to the necking initiation and thus postpones necking. Correspondingly, a decrease in tensile load is observed in this case. This paper investigates the effect of thickness stress on the formability of aluminum alloy metal sheets using crystal plasticity finite element analysis. A self-hardening behavior is considered for the slip systems. Further, for the prediction of necking initiation and growth, the maximum shear strain criterion is used for damage initiation and evolution. In order to implement the model in Abaqus finite element package, a VUMAT was developed based on the discretized equations and forward Euler integration scheme. After verification of the developed code, the parameters of the model were calibrated against the tensile test results. For simulating tensile test of 1 mm thick sheet, a representative volume of 3×1.5×0.5 mm3،was partitioned into 14790 grains through a python code in ABAQUS/CAE environment and then discretized using 50 μm tetrahedral linear elements. Using the experimental data available in the literature and considering appropriate texture for the simulation domain, the crystal orientations were assigned through Euler angles. Then, tensile tests were performed on the sample in the presence of the thickness pressure stress. The results show that application of the through thickness stress increases the strain corresponding to the necking initiation and thus postpones necking. Correspondingly, a decrease in tensile load is observed in this case.

https://mej.aut.ac.ir/article_4517_7109af321d970c64a0154000a60e65c8.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Experimental Extraction of Young's Modulus of MCF-7 Breast Cancer Cell Using Spherical Contact Models Experimental Extraction of Young's Modulus of MCF-7 Breast Cancer Cell Using Spherical Contact Models 5769 5784 4528 10.22060/mej.2021.19993.7149 FA Moein Taheri Department of Engineering, Arak University, Arak, Iran 0000-0001-6583-3925 Mahdi Mirzaluo Department of Engineering, Arak University, Arak, Iran Journal Article 2021 05 03 Breast cancer is one of the most important cancers in the field of medicine due to its high prevalence. Understanding the mechanical properties of cellular tissue, including Young's modulus, and comparing the differences created after the onset of the disease, lead to the development of new methods in recognizing, controlling, and treating the disease. Nanomanipulation is one of the processes used in the field of nanotechnology, which explores the properties of cellular tissues. An atomic force microscope is a tool used during this process that examines the properties of cellular tissue by measuring the movement of the cantilevers and the changes due to displacement and force. In this study, nanomanipulation of MCF-7 breast cancer cells was performed experimentally using an atomic force microscope with the aim of finding the Young modulus of cell tissue. After extracting the experimental results, modeling and calculating the critical force and time by considering different contact models including the Hertz contact model, PT, and COS, has been done. According to the comparison of experimental and simulation results, Young's modulus of MCF-7 breast cancer cells was obtained in the range of 800 Pa. Also, the COS contact model was more in line with the experimental results. Breast cancer is one of the most important cancers in the field of medicine due to its high prevalence. Understanding the mechanical properties of cellular tissue, including Young's modulus, and comparing the differences created after the onset of the disease, lead to the development of new methods in recognizing, controlling, and treating the disease. Nanomanipulation is one of the processes used in the field of nanotechnology, which explores the properties of cellular tissues. An atomic force microscope is a tool used during this process that examines the properties of cellular tissue by measuring the movement of the cantilevers and the changes due to displacement and force. In this study, nanomanipulation of MCF-7 breast cancer cells was performed experimentally using an atomic force microscope with the aim of finding the Young modulus of cell tissue. After extracting the experimental results, modeling and calculating the critical force and time by considering different contact models including the Hertz contact model, PT, and COS, has been done. According to the comparison of experimental and simulation results, Young's modulus of MCF-7 breast cancer cells was obtained in the range of 800 Pa. Also, the COS contact model was more in line with the experimental results.

https://mej.aut.ac.ir/article_4528_59112692262234e3fad47fa8eabf03a4.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 A Fast Warehouse Inventory Micro Aerial Vehicle System Equipped with Visual Guidance and Navigation Algorithm A Fast Warehouse Inventory Micro Aerial Vehicle System Equipped with Visual Guidance and Navigation Algorithm 5785 5808 4602 10.22060/mej.2021.19428.7022 FA Hamidreza Fahimi Flight Dynamics and Control, Department of Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran Abolghasem Naghash Department of Aerospace Engineering, Amirkabir University of Technology 0000-0001-7776-7662 Journal Article 2020 12 28 This paper is an attempt to integrate computer vision techniques and micro aerial vehicle guidance to design and optimize an automated mission performed by a light micro aerial vehicle such that automating the mission becomes reasonably more efficient than performing it manually. A system is provided for warehouse management using a micro aerial vehicle equipped with a front camera. Computer vision algorithms make it possible for the micro aerial vehicle to locate packages, verify the presence or absence of a specified package and list the entire warehouse inventory in a short time. An innovative method is provided to detect shelves and their packages by the camera image, which enables the system to instantly plan the shortest path for the micro aerial vehicle while performing a shelf inventory listing. Then, following the planned path completes the mission faster than conventional guidance methods. The guidance algorithm is designed such that the efficiency of automatic operations compared to human operations is significantly increased. The system is first simulated and then implemented and the test output data is provided. The tests indicate the success of the system in securing automated operations while decreasing mission time. This paper is an attempt to integrate computer vision techniques and micro aerial vehicle guidance to design and optimize an automated mission performed by a light micro aerial vehicle such that automating the mission becomes reasonably more efficient than performing it manually. A system is provided for warehouse management using a micro aerial vehicle equipped with a front camera. Computer vision algorithms make it possible for the micro aerial vehicle to locate packages, verify the presence or absence of a specified package and list the entire warehouse inventory in a short time. An innovative method is provided to detect shelves and their packages by the camera image, which enables the system to instantly plan the shortest path for the micro aerial vehicle while performing a shelf inventory listing. Then, following the planned path completes the mission faster than conventional guidance methods. The guidance algorithm is designed such that the efficiency of automatic operations compared to human operations is significantly increased. The system is first simulated and then implemented and the test output data is provided. The tests indicate the success of the system in securing automated operations while decreasing mission time.

https://mej.aut.ac.ir/article_4602_fd00d3474e495e7b6d5f9f575b2d7ec4.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Modeling and Flutter Analysis of a Three Dimensional Box-Wing using Wagner Unsteady Aerodynamic Model Modeling and Flutter Analysis of a Three Dimensional Box-Wing using Wagner Unsteady Aerodynamic Model 5809 5830 4591 10.22060/mej.2021.19690.7092 FA Amirhossein Ghasemikaram Mechanical Engineering Faculty, Yazd University, Yazd, Iran Abbas Mazidi Mechanical Engineering Faculty, Yazd University, Yazd, Iran S. Ahmad Fazelzadeh Haghighi Mechanical Engineering Faculty, Shiraz University, Shiraz, Iran Journal Article 2021 03 06 In this paper, a three dimensional model of a box wing configuration is derived by a semi-analytical approach and the aeroelastic behavior is studied. So far, the flutter characteristics have been studied on the typical wing sections or via a whole lot more time and cost in the professional software. The winglet is modeled by two longitudinal and torsional springs and in order to simulate the effect of the winglet on the dynamic behavior, two ends of the springs are placed on the elastic axis of the sections. The governing equations are extracted via Hamilton's principle and in order to apply the aerodynamic forces, Wagner unsteady model is considered. To transform the linear partial integro-differential equations into a set of ordinary differential equations, mathematical techniques are employed. For the purpose of validation, the flutter values of the box wing are obtained by MSC NASTRAN and the proposed numerical procedure. The effects of the sweep angles and the winglet rigidity on the flutter are investigated. The results reveal that increasing the sweep angles and the chord ratio, enhances the flutter speed, remarkably. Furthermore, increasing the torsional rigidity of the winglet is more significant than the longitudinal rigidity on the flutter. In this paper, a three dimensional model of a box wing configuration is derived by a semi-analytical approach and the aeroelastic behavior is studied. So far, the flutter characteristics have been studied on the typical wing sections or via a whole lot more time and cost in the professional software. The winglet is modeled by two longitudinal and torsional springs and in order to simulate the effect of the winglet on the dynamic behavior, two ends of the springs are placed on the elastic axis of the sections. The governing equations are extracted via Hamilton's principle and in order to apply the aerodynamic forces, Wagner unsteady model is considered. To transform the linear partial integro-differential equations into a set of ordinary differential equations, mathematical techniques are employed. For the purpose of validation, the flutter values of the box wing are obtained by MSC NASTRAN and the proposed numerical procedure. The effects of the sweep angles and the winglet rigidity on the flutter are investigated. The results reveal that increasing the sweep angles and the chord ratio, enhances the flutter speed, remarkably. Furthermore, increasing the torsional rigidity of the winglet is more significant than the longitudinal rigidity on the flutter.

https://mej.aut.ac.ir/article_4591_f58c9875ac84dfe1fbe91b918773d050.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Robust and Adaptive Control of an Exoskeleton Robot For Tracking Modified Desired Trajectory Based on Zero Moment Point Stability Theory Robust and Adaptive Control of an Exoskeleton Robot For Tracking Modified Desired Trajectory Based on Zero Moment Point Stability Theory 5831 5850 4569 10.22060/mej.2021.19761.7106 FA Majid Mokhtari School of Mechanical engineering, ShahidBeheshti University, Tehran, Iran Mostafa Taghizadeh shahid beheshti university Mahmood Mazare School of Mechanical Engineering, ShahidBeheshtiUniversity, Tehran, Iran. Journal Article 2021 03 19 The Creation of reference trajectories and the ability to track them in the presence of disturbances and uncertainties are important issues in investigating the exoskeleton performance. One of the methods of trajectory planning is the central pattern generation algorithm. This algorithm will behave in a limit cycle and the temporal disturbances have quickly removed the system and created harmonious trajectories. In this paper, for the creation of reference trajectories of each joint, a combination of seven modified Hopfield oscillators is used which provides the ability to change the frequency and domain of walking. Online modification of robot joint reference trajectories is done by using the feedback error signal between desired zero momentum point and zero momentum point of the robot at any moment. In order to cope with the disturbances and uncertainty with the uncertain domain and achieve maximum efficiency in tracking robot reference trajectories, an adaptive dynamic fast terminal sliding mode controller is used due to the elimination of chattering phenomena, and finite-time convergence. Also, by moving the Upper link the maximum stability of the robot based on the zero momentum point criterion is guaranteed. To achieve maximum performance, controller parameters, oscillator coefficients, and connections between them are optimized. Finally, the performance of the proposed method is compared with a sliding mode controller. The results demonstrate the superiority of the proposed method. The Creation of reference trajectories and the ability to track them in the presence of disturbances and uncertainties are important issues in investigating the exoskeleton performance. One of the methods of trajectory planning is the central pattern generation algorithm. This algorithm will behave in a limit cycle and the temporal disturbances have quickly removed the system and created harmonious trajectories. In this paper, for the creation of reference trajectories of each joint, a combination of seven modified Hopfield oscillators is used which provides the ability to change the frequency and domain of walking. Online modification of robot joint reference trajectories is done by using the feedback error signal between desired zero momentum point and zero momentum point of the robot at any moment. In order to cope with the disturbances and uncertainty with the uncertain domain and achieve maximum efficiency in tracking robot reference trajectories, an adaptive dynamic fast terminal sliding mode controller is used due to the elimination of chattering phenomena, and finite-time convergence. Also, by moving the Upper link the maximum stability of the robot based on the zero momentum point criterion is guaranteed. To achieve maximum performance, controller parameters, oscillator coefficients, and connections between them are optimized. Finally, the performance of the proposed method is compared with a sliding mode controller. The results demonstrate the superiority of the proposed method.

https://mej.aut.ac.ir/article_4569_f1920129f9c75b3d604ea4874e120736.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Out-of-Plane Vibration Mitigation of Wind Turbine Blade Using Highly Efficient Nonlinear Energy Sink Out-of-Plane Vibration Mitigation of Wind Turbine Blade Using Highly Efficient Nonlinear Energy Sink 5851 5866 4533 10.22060/mej.2021.19784.7111 FA Maziyar Daghighi School of Mechanical Engineering, Shahid Rajaee teacher training Uni. Ali Rahmani Hanzaki Faculty member with Mechanical engineering faculty, Shahid Rajaeeteacher training Uni. 0000-0002-2895-7176 Majid Shahgholi School of Mechanical Engineering-Shahid Rajaee teacher training Uni. Tehran-Iran 0000-0002-1134-068X Saeed Bab Niroo Research Institute,-Tehran-Iran Journal Article 2021 03 23 Nowadays, the use of wind as one of the main sources of low carbon and renewable energy is expanding rapidly all around the world. Recently, with the development of wind farms and the increase in the size of wind turbines, the wind loads on them have increased, and as a result, they have become more difficult and expensive to maintain. Therefore, researchers have deeply focused on the analysis and the control of their vibration. In this study, a wind turbine blade with a type of nonlinear absorber, called highly efficient nonlinear energy sink is analyzed, furthermore the interaction between the heavy and long blade and the nonlinear energy sink, under the influence of gravity in the vertical plane and time-dependent wind force, which is due to its height dependency is examined. For this purpose, the equations of motion of the system are obtained by the energy method and solved numerically. The blade- nonlinear energy sink system behavior is compared to that of the blade and linear absorber system. Also, the sensitivity of the parameters affecting the performance of the nonlinear energy sink is analyzed and the vibration of the system with optimized nonlinear energy sink is compared with the alone blade and the blade with the optimal linear absorber behaviors. Nowadays, the use of wind as one of the main sources of low carbon and renewable energy is expanding rapidly all around the world. Recently, with the development of wind farms and the increase in the size of wind turbines, the wind loads on them have increased, and as a result, they have become more difficult and expensive to maintain. Therefore, researchers have deeply focused on the analysis and the control of their vibration. In this study, a wind turbine blade with a type of nonlinear absorber, called highly efficient nonlinear energy sink is analyzed, furthermore the interaction between the heavy and long blade and the nonlinear energy sink, under the influence of gravity in the vertical plane and time-dependent wind force, which is due to its height dependency is examined. For this purpose, the equations of motion of the system are obtained by the energy method and solved numerically. The blade- nonlinear energy sink system behavior is compared to that of the blade and linear absorber system. Also, the sensitivity of the parameters affecting the performance of the nonlinear energy sink is analyzed and the vibration of the system with optimized nonlinear energy sink is compared with the alone blade and the blade with the optimal linear absorber behaviors.

https://mej.aut.ac.ir/article_4533_56a8da1d3bcb2e9b334a778be5b1d781.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 12 2022 02 20 Free and Forced Vibration Analysis of Stiffened Cylindrical Shells under Moving Internal Pressure Free and Forced Vibration Analysis of Stiffened Cylindrical Shells under Moving Internal Pressure 5867 5886 4583 10.22060/mej.2021.19846.7138 FA Reza Arab MSc student, Mechanical Engineering,- Malek Ashtar University of Technology (MUT), -Tehran,- Iran Hosein Lexian Malek-e-Ashtar University of Technology/ Faculty of Materials &amp; Manufacturing Processes Journal Article 2021 04 19 Cylindrical shells are used tremendously in many engineering fields such as ships, submarines, and fuel tanks in airplanes. In many cases, shells are exposed to dynamic loads. One of the dynamic loads in shells is internal moving pressure. Analysis of cylindrical stiffened shells under moving internal pressure are investigated in this research. Equations of motion are based on classic shell theory and derived from Hamilton’s method. Boundary conditions are assumed simply support. Displacement components are assumed Fourie double series based on boundary conditions. Equations of motions are solved by Galerkin weighted functions method for calculation of natural frequency and dynamic response of cylindrical shells under moving internal pressure. Codes in FORTRAN are used to derive the natural frequency and dynamic response of cylindrical shells. Results are compared with other references and Abaqus software. The effect of geometrical parameters on natural frequency and dynamic response of cylindrical shells under moving internal pressure are investigated finally and results for stiffened shells and unstiffened shells with different stiffeners are compared. Cylindrical shells are used tremendously in many engineering fields such as ships, submarines, and fuel tanks in airplanes. In many cases, shells are exposed to dynamic loads. One of the dynamic loads in shells is internal moving pressure. Analysis of cylindrical stiffened shells under moving internal pressure are investigated in this research. Equations of motion are based on classic shell theory and derived from Hamilton’s method. Boundary conditions are assumed simply support. Displacement components are assumed Fourie double series based on boundary conditions. Equations of motions are solved by Galerkin weighted functions method for calculation of natural frequency and dynamic response of cylindrical shells under moving internal pressure. Codes in FORTRAN are used to derive the natural frequency and dynamic response of cylindrical shells. Results are compared with other references and Abaqus software. The effect of geometrical parameters on natural frequency and dynamic response of cylindrical shells under moving internal pressure are investigated finally and results for stiffened shells and unstiffened shells with different stiffeners are compared.

https://mej.aut.ac.ir/article_4583_33805671920f0d02e6d18f630985aace.pdf