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DYNAmIC PULL-IN INSTABILITY OF DOUBLE-SIDED ACTUATED NANO-TORSIONAL SWITCHES

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Acta mechanica Solida Sinica 2015年第1期28卷 91-101页

作者： hamid m.sedighi Kourosh H.Shirazi Department of mechanical Engineering Shahid Chamran University

A nonlinear frequency-amplitude relation is developed to investigate the vibrational amplitude effect on the dynamic pull-in instability of double-sided-actuated nano-torsional switches. The governing equation of a nano-electro-mechanical system pre-deformed by an electric field contains the quintic nonlinear term. The influences of basic parameters on the pull-in instability and natural frequency are investigated using a powerful analytical approach called the homotopy perturbation method. It is demonstrated that two terms in series expansion are sufficient to produce an acceptable solution. The numerical results obtained have verified the soundness of the asymptotic procedure. The phase portraits of the double-sided nano-torsionalactuator exhibit periodic, homoclinic and heteroclinic orbits.

关键词： homotopy perturbation method frequency-amplitude relationship double-sidedactuated nano-switch dynamic pull-in instability homoclinic orbit heteroclinic orbit

Velocity gradient elasticity for nonlinear vibration of carbon nanotube resonators

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Frontiers of Structural and Civil Engineering 2020年第6期14卷 1520-1530页

作者： hamid msedighi Hassen mOUAKAD mechanical Engineering Deparment Faculty of Engineering Shahid Chamran University of AhvazAhvaz ***Iran Driling Center of Exellence and Research Center Shahid Chamran University of AhvazAhvaz ***Iran mechanical and Industrial Engineering Department Collge of EngineeringSultan Qaboos UniversitMuscalOMAN

In this study,for the first time,we investigate the nonlocality superimposed to the size effects on the nonlinear dynamics of an electrically actuated single-walled carbon-nanotube-based *** undertake two models to capture the nanostructure nonlocal size effects:the strain and the velocity gradient *** use a reduced-order model based on the differential quadrature method(DQm)to discretize the goverming nonlinear equation of motion and acquire a discretized-parameter nonlinear model of the *** structural nonlinear behavior of the system assuming both strain and velocity gradient theories is investigated using the discretized *** results suggest that nonlocal and size effects should not be neglected because they improve the prediction of corresponding dynamic amplitudes and,most importantly,the critical resonant frequencies of such *** these effects may impose a considerable source of error,which can be amended using more accurate modeling techniques.

关键词： velocity gradient elasticity theory nanotube resonators differential-quadrature method nonlinear vibration

Experimental and theoretical investigations of the lateral vibrations of an unbalanced Jeffcott rotor

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Frontiers of Structural and Civil Engineering 2020年第4期14卷 1024-1032页

作者： Ali ALSALEH hamid msedighi Hassen mOUAKAD Saudi Arabian Oil Company(ARAmCO) Dhahran 31311Saudi Arabia mechanical Engineering Deparment Faculty of EngineeringShahid Chamran University of AhvazAhvaz 61357-43337Iran Drilling Center of Excellence and Research Shahid Chamran University of AhvazAhvaz 61357-43337Iran mechanical and Industrial Engineering Deparment Sultan Qaboos UniversinAI Khoudh MuscatOman

The current work experimentally explores and then theoretically examines the lateral vibrations of an unbalanced Jeffcott rotor-system working at several unbalance *** this end,three conditions of eccentric masses are considered by using a Bently Nevada RK-4 rotor *** of the steady-state as well as the startup data at rigid and flexible rotor states are captured by conducting a setup that mimics the vibration monitoring industrial *** linear governing equation of the considered rotor is extracted by adopting the Lagrange method on the basis of rigid rotor assumptions to theoretically predict the lateral *** dynamic features of the rotor system such as the linearized bearing induced stiffness are exclusively acquired from startup *** is demonstrated that,with an error of less than 5%,the proposed two-degrees-of-freedom model can predict the flexural vibrations at rigid *** at flexible condition,it fails to accurately predict the dynamic *** contrast to the other works where nonlinear mathematical models with some complexities are proposed to mathematically model the real systems,the present study illustrates the applicability of employing simple models to predict the dynamic response of a real rotor-system with an acceptable accuracy.

关键词： rotor-dynamics Jeffcott rotor lateral vibrations Lagrange method system-equivalent stfess sleeve bearings il film induced stiffness

Strain-Rate Dependency of a Unidirectional Filament Wound Composite under Compression

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Computer modeling in Engineering & Sciences 2023年第12期137卷 2149-2161页

作者： Stepan Konev Victor A.Eremeyev hamid m.sedighi Leonid Igumnov Anatoly Bragov Aleksandr Konstantinov Ayaulym Kuanyshova Ivan Sergeichev Skolkovo Institute of Science and Technologies Center for Materials TechnologiesMoscowRussia National Research Lobachevsky State University of Nizhny Novgorod Nizhny NovgorodRussia Dipartimento di Ingegneria Civile Ambientale e Architettura(DICAAR)Universitàdegli Studi di CagliariCagliari(CA)Italy mechanical Engineering Department Faculty of EngineeringShahid Chamran University of AhvazAhvazIran Drilling Center of Excellence and Research Center Shahid Chamran University of AhvazAhvazIran

This article presents the results of experimental studies concerning the dynamic deformation and failure of a unidirectional carbon fiber reinforced plastic(T700/LY113)under *** test samples were manufactured through the filament winding of flat *** establish the strain rate dependencies of the strength and elastic modulus of the material,dynamic tests were carried out using a drop tower,the Split Hopkinson Pressure Bar method,and standard static *** samples were loaded both along and perpendicular to the direction of the reinforcing *** applicability of the obtained samples for static and dynamic tests was confirmed through finite elementmodeling and the high-speed imaging of the deformation and failure of samples during *** a result of the conducted experimental studies,static and dynamic stress-strain curves,time dependencies of deformation and the stress and strain rates of the samples during compression were *** on these results,the strain rate dependencies of the strength and elasticity modulus in the strain rate range of 0.001-6001/s are *** is shown that the strain rate significantly affects the strength and deformation characteristics of the unidirectional carbon fiber composites under *** increase in the strain rate by 5 orders of magnitude increased the strength and elastic modulus along the fiber direction by 42%and 50%,*** loading resulted in a strength and elastic modulus increase by 58%and 50%,*** average strength along the fibers at the largest studied strain rate was about *** obtained results can be used to design structural elements made of polymer composite materials operating under dynamic shock loads,as well as to build models of mechanical behavior and failure criteria of such materials,taking into account the strain rate effects.

关键词： High strain rate composites filament winding dynamic strength Split Hopkinson Pressure Bar compression

In vitro corrosion-fatigue behavior of biodegradable mg/HA composite in simulated body fluid

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Journal of magnesium and Alloys 2021年第6期9卷 2169-2184页

作者： E.Ghazizadeh A.H.Jabbari m.sedighi School of mechanical Engineering Iran University of Science and TechnologyNarmakTehranIran

magnesium and its composites as biodegradable materials offer especial capabilities to be used as bio-absorbable ***,their poor corrosion and fatigue properties in the physiological environment can restrict their *** this study,corrosion-fatigue tests have been performed on the extruded magnesium and magnesium/hydroxyapatite(mg/HA)composites in a high cycle *** produce the composites,pure magnesium was reinforced by 2.5 wt.%and 5 wt.%of hydroxyapatite submicron particles using an electromagneticmechanical stirring method and hot extrusion *** experimental density measurement exhibits that the porosity increases in the extruded samples with more hydroxyapatite *** investigate the corrosion and corrosion-fatigue behavior of the specimens,simulated body fluid(SBF)was used during in vitro *** results of the potentiodynamic polarization corrosion test show that the composite with 2.5 wt.%of hydroxyapatite(mg/2.5 wt.%HA)and the pure magnesium specimen exhibit the highest and the lowest corrosion resistance,*** the elemental mapping analysis of the corroded samples,this behavior could be due to the formation of strong phosphorus-calcium based layers on the composite *** results obtained from the mechanical tests indicate that mg/5 wt.%HA offered the highest tensile and compressive yield strengths,as well as the most promising high cycle fatigue *** the corrosionfatigue test,the simultaneous effects of fatigue and corrosion damages led to a similar corrosion-fatigue behavior in both *** fracture surfaces of the corrosion-fatigue samples suggest that the cracks are initiated in the corroded regions of the samples surface,which reduces the crack initiation step and subsequently decreases the fatigue *** comparison with the pure magnesium,both composites exhibit more promising corrosion and corrosion-fatigue behaviors with a significant fatigue life improvement in the ph

关键词： magnesium magnesium/Hydroxyapatite composite Corrosion Biodegradation High cycle fatigue Corrosion-fatigue

Severe plastic deformation (SPD) of biodegradable magnesium alloys and composites: A review of developments and prospects

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Journal of magnesium and Alloys 2022年第4期10卷 938-955页

作者： m.Kasaeian-Naeini m.sedighi R.Hashemi School of mechanical Engineering Iran University of Science and TechnologyTehranIran

The use of magnesium in orthopedic and cardiovascular applications has been widely attracted by diminishing the risk of abnormal interaction of the implant with the body tissue and eliminating the second surgery to remove it from the ***,the fast degradation rate and generally inhomogeneous corrosion subsequently caused a decline in the mechanical strength of mg during the healing *** researches have been conducted on the influences of various severe plastic deformation(SPD)processes on magnesium bioalloys and *** paper strives to summarize the various SPD techniques used to achieve magnesium with an ultrafine-grained(UFG)***,the effects of various severe plastic deformation methods on magnesium microstructure,mechanical properties,and corrosion behavior have been ***,this review intends to clarify the different potentials of applying SPD processes to the magnesium alloys and composites to augment their usage in biomedical applications.

关键词： magnesium Severe plastic deformation Biodegradable implant mechanical properties Corrosion

Static and Dynamic Pull-In Instability of Nano-Beams Resting on Elastic Foundation Based on the Nonlocal Elasticity Theory

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Chinese Journal of mechanical Engineering 2017年第2期30卷 385-397页

作者： hamid m.sedighi ASHKAN Sheikhanzadeh mechanical Engineering Department Faculty of EngineeringShahid Chamran University of Ahvaz Departmentof mechanical Engineering Najafabad BranchIslamic Azad Univesity

This paper provides the static and dynamic pullin behavior of nano-beams resting on the elastic foundation based on the nonlocal theory which is able to capture the size effects for structures in micron and sub-micron scales. For this purpose, the governing equation of motion and the boundary conditions are driven using a variational approach. This formulation includes the influences of fringing field and intermolecular forces such as Casimir and van der Waals forces. The differential quadrature （DQ） method is employed as a high-order approximation to discretize the governing nonlinear differential equation, yielding more accurate results with a Considerably smaller number of grid points. In addition, a powerful analytical method called parameter expansion method （PEm） is utilized to compute the dynamic solution and frequency-amplitude relationship. It is illustrated that the first two terms in series expansions are sufficient to produce an acceptable solution of the mentioned structure. Finally, the effects of basic parameters on static and dynamic pull-in insta- bility and natural frequency are studied.

关键词： Static and dynamic pull·in voltages Size dependent Nonlocal theory Euler·Bernoulli beam model Differential quadrature method Parameter Expansion method

Effect of stiffeners on crashworthiness of square aluminium columns considering damage evolution

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Journal of Central South University 2013年第3期20卷 599-607页

作者： H.R.Allahbakhsh m.Shariati m.sedighi mechanical Department Damghan BranchIslamic Azad UniversityDamghan 36716-39998Iran mechanical Department Ferdowsi University of MashhadMashhad 91779-48974Iran

Combining the optimization and FEm technology,crashworthiness of aluminum extrusions was studied for an automobile safety *** effects of longitudinal stiffeners on the crushing of stiffened square columns were studied considering the damage *** numerical analysis was carried out by ABAQUS ***,the collapse behavior of aluminum extrusion damage was validated by comparing against solution published in ***,in order to find more efficient and lighter crush absorber and achieving minimum peak crushing force,response surface methodology(RSm) has been applied for optimizing the aluminum extrusion tube.

关键词： damage response surface methodology (RSm) crashworthiness stiffener

Designing of ECAP parameters based on strain distribution uniformity

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Progress in Natural Science:materials International 2012年第5期22卷 452-460页

作者： F.Djavanroodi B.Omranpour m.Ebrahimi m.sedighi Department of mechanical Engineering Iran University of Science and TechnologyTehranIran

Equal Channel Angular Pressing(ECAP) is currently one of the most popular methods for fabricating Ultra-Fine Grained(UFG) *** this work,ECAP process has been performed on commercial pure aluminum up to 8 passes by route *** verification of FEm work,the influences of four die channel angles,three outer corner angles and pass number up to 8 have been analyzed to investigate strain distribution behavior of ECAPed *** methods for quantifying the strain homogeneity namely inhomogeneity index(Ci) and standard deviation(S.D.) are *** is shown that Ci is not a good candidate for examining the strain distribution ***,it is suggested that designing of ECAP die geometry to achieve optimum strain distribution homogeneity is more suitable than the optimum effective strain *** best strain distribution uniformity in the transverse plane is obtained with Ф=60° and Ψ=15° and for the bulk of the sample,Ф=120° and Ψ=15° or 60°,gives the highest strain dispersal uniformity.

关键词： ECAP FEm Die design Strain distribution