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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

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

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

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

PCL/HA静电纺丝纤维涂层对可降解mg/HA复合材料的表面改性:力学性能、腐蚀和生物相容性

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Transactions of Nonferrous metals Society of China 2024年第5期34卷 1470-1486页

作者： m.SHAmSI m.sedighi A.BAGHERI School of mechanical Engineering Iran University of Science and TechnologyTehranIran

采用搅拌铸造和挤压法制备mg/HA复合材料,并在其表面采用静电纺丝法涂覆聚己内酯/羟基磷灰石(PCL/HA)纤维(2.5%和5%HA,质量分数),以提高其耐腐蚀性。力学性能测试结果表明,复合材料的压缩屈服强度从73mPa(纯镁)提高到151mPa,提高了107%... 详细信息

采用搅拌铸造和挤压法制备mg/HA复合材料,并在其表面采用静电纺丝法涂覆聚己内酯/羟基磷灰石(PCL/HA)纤维(2.5%和5%HA,质量分数),以提高其耐腐蚀性。力学性能测试结果表明,复合材料的压缩屈服强度从73mPa(纯镁)提高到151mPa,提高了107%。SEm、EDS和XRD分析表明,HA颗粒分布在多孔涂层中。极化曲线结果表明,涂层试样的耐腐蚀性能均优于未涂覆试样。PCL涂层使样品的腐蚀电流密度降低了两个数量级。通过极化和体外腐蚀试验证明了HA在涂层中的有效性。涂层和随后形成的Ca-P层阻碍了模拟体液与基体的接触和渗透,从而起到保护表面的作用。PCL/2.5%HA涂层样品的腐蚀速率最低,其平均值为0.98mm/a,与未涂层样品相比,在14天内减少了81%。根据3天mTT结果,使用PCL/2.5%HA涂层可使细胞活性从43%提高到121%。综上,涂覆PCL/2.5%HA纤维的mg/HA复合材料在生物可吸收植入物方面具有广阔的应用前景。

关键词：镁基复合材料复合涂层生物可降解羟基磷灰石聚己内酯纤维

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Effect of nano-sized Al2O3 reinforcing particles on uniaxial and high cycle fatigue behaviors of hot-forged AZ31B magnesium alloy

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Transactions of Nonferrous metals Society of China 2020年第5期30卷 1249-1266页

作者： m.DAREINI A.H.JABBARI m.sedighi School of mechanical Engineering Iran University of Science and TechnologyNarmakTehran ***Iran

The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.

关键词： magnesium matrix nanocomposite AZ31B alloy nano-sized Al2O3 open-die hot-forging high cycle fatigue mechanical properties microstructural evolution

Process parameter effects on microstructure and mechanical properties of tubes processed via friction assisted tube straining method

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Journal of Central South University 2021年第10期28卷 3008-3017页

作者： S.H.HOSSEINI m.sedighi School of mechanical Engineering Iran University of Science and TechnologyTehran 16846-13114Iran

This paper investigates process parameter effects on microstructure and mechanical properties of the tubes processed via recently developed friction assisted tube straining(FATS)*** this purpose,design of experiment was used to arrange finite element analyses and experimental *** and experimental tests were executed by changing rotary speed,feed rate and die *** design results show that increasing feed rate and decreasing rotary speed enhance Zener-Hollomon(Z)parameter and decrease average grain size,while die angle has no considerable *** Z value reduces grain size and enhances flow stress of the processed samples,while the experiment with the highest Z value refines initial microstructure from 40 to 8μm and increases flow stress by 5 times.

关键词： friction assisted tube straining process parameter microstructure Taguchi method finite element simulation