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Model of contact friction based on extreme value statistics

Friction 2019年第4期7卷 327-339页

作者： a.malekan S.ROUHANI Department of Physics Sharif University of Technology

We propose a model based on extreme value statistics(EVS) and combine it with different models for single-asperity contact, including adhesive and elasto-plastic contacts, to derive a relation between the applied load and the friction force on a rough interface. We determine that, when the summit distribution is Gumbel and the contact model is Hertzian, we obtain the closest conformity with Amonton’s law. The range over which Gumbel distribution mimics Amonton’s law is wider than that of the Greenwood–Williamson(GW) model. However, exact conformity with Amonton’s law is not observed for any of the well-known EVS distributions. Plastic deformations in the contact area reduce the relative change in pressure slightly with Gumbel distribution. Interestingly, when elasto-plastic contact is assumed for the asperities, together with Gumbel distribution for summits, the best conformity with Amonton’s law is achieved. Other extreme value statistics are also studied, and the results are presented. We combine Gumbel distribution with the GW–McC ool model, which is an improved version of the GW model, and the new model considers a bandwidth for wavelengths α. Comparisons of this model with the original GW–McCool model and other simplified versions of the Bush–Gibson–Thomas theory reveal that Gumbel distribution has a better conformity with Amonton’s law for all values of α. When the adhesive contact model is used, the main observation is that there is some friction for zero or even negative applied load. Asperities with a height even less than the separation between the two surfaces are in contact. For a small value of the adhesion parameter, a better conformity with Amonton’s law is observed. The relative pressure increases for stronger adhesion, which indicates that adhesion-controlled friction is dominated by load-controlled friction. We also observe that adhesion increases on a surface with a lower value of roughness.

关键词： Amonton’s law contact mechanics extreme value statistics friction

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Microstructural evaluation of Hastelloy-X transient liquid phase bonded joints:Effects of filler metal thickness and holding time

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Transactions of Nonferrous Metals Society of China 2022年第5期32卷 1548-1558页

作者： a.malekan S.E.MIRSALEHI M.FARVIZI N.SAITO K.NAKASHIMA Ceramic Division Materials and Energy Research CenterP.O.Box 14155-4777TehranIran Department of Materials and Metallurgical Engineering Amirkabir University of Technology(Tehran Polytechnic)Tehran 15875-4413Iran Department of Materials Science and Engineering Kyushu University744MotookaNishi-kuFukuoka 819-0395Japan

Transient liquid phase(TLP)bonding was investigated in Hastelloy-X samples with different filler metal thicknesses(20,35,50,65,and 100μm)and holding time(5,20,80,320,and 640 min)to obtain optimum bonding *** evaluations using electron probe microanalysis(EPMA)and electron backscattered diffraction(EBSD)show that the central eutectic phases present in the athermally solidified zone(ASZ)are Ni_(3)B,Ni_(2)Si,and CrB,and the precipitates formed in the diffusion-affected zone(DAZ)are MoB,CrB_(2),and Mo_(2)B_(5).According to the results,decreasing the filler thickness as well as increasing the holding time helps realize the completion of isothermal solidification and reduction in the density of precipitates in the DAZ,leading to a joint with more uniform *** of boron and silicon to longer distances with increasing holding time causes the removal of Cr-rich borides in the DAZ and the formation of Mo-rich silicide at the joint *** in hardness of ASZ and DAZ due to the elimination of brittle phases in these zones during long holding time causes more uniform hardness distribution in the joint *** best results are obtained for the sample joined with the 35μm-thick filler metal for 640 min holding time.

关键词： Hastelloy-X transient liquid phase(TLP)bonding microstructure filler metal electron probe microanalysis(EPMA) electron backscattered diffraction(EBSD)

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Preparation of tungsten-particle-reinforced Zr-based bulk metallic glass composites by two-step spark plasma sintering:microstructure evolution,densification mechanism and mechanical properties

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Rare Metals 2024年第4期43卷 1793-1808页

作者： Yun-Fei Ma Pan Gong Mao Zhang Hui-EHu Zhen Peng Xiao Xu Xin Wang Mehdi malekan Xue-Feng Tang Lei Deng Jun-Song Jin Xin-Yun Wang State Key Laboratory of Materials Processing and Die and Mould Technology School of Materials Science and EngineeringHuazhong University of Science and TechnologyWuhan430074China Research Institute of Huazhong University of Science and Technology in Shenzhen Shenzhen518057China Department of Chemistry and Materials Naval University of EngineeringWuhan430032China School of Materials Science and Engineering Jiangsu UniversityZhenjiang212013China College of Machine Shanghai Dianji UniversityShanghai201306China School of Metallurgy and Materials Engineering College of EngineeringUniversity of TehranTehran 11155-4563Iran

A new two-step spark plasma sintering(TSS)process with low-temperature pre-sintering and high-temperature final sintering has been successfully applied to prepare the tungsten-particle(Wp)-reinforced bulk metallic glass composites(Wp/BMGCs).Compared to normal spark plasma sintering(NS),the densification rate and relative density of Wp/BMGCs can be improved by selecting TSS with appropriate sintering pressure in the low temperature pre-sintering ***,the compressive strength and plastic strain of 30%Wp/BMGCs prepared by TSS are both higher than those of the samples prepared by *** TSS process can significantly enhance the compressive strength of 30%Wp/BMGCs by 12%and remarkably increase the plastic strain by 50%,while the trend is completely opposite for 50%Wp/***-in situ experiments and finite element simulations reveal that uneven temperature distribution among particles during low-temperature pre-sintering causes local overheating at contact points between particles,accelerating formation of sintering neck between particles and plastic deformation of *** the volume fraction of Wp is low,TSS can improve the interface bonding between particles by increasing the number of sintering *** makes the fracture mode of Wp/BMGCs being predominantly transgranular ***,as the volume fraction of Wp increases,the adverse effects of Wp plastic deformation are becoming more and more *** aggregated Wp tends to form a solid"cage structure"that hinders the bonding between particles at the interface;correspondingly,the fracture behavior of Wp/BMGCs is mainly dominated by intergranular ***,reducing the sintering pressure during the low-temperature pre-sintering stage of TSS has been shown to effectively decrease plastic deformation in Wp,resulting in a higher degree of densification and better mechanical properties.

关键词： Bulk metallic glass composites Tungsten particle Two-step spark plasma sintering Densification mechanism Mechanical properties

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In-vitro corrosion behavior of the cast and extruded biodegradable Mg-Zn-Cu alloys in simulated body fluid(SBF)

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Journal of Magnesium and Alloys 2021年第6期9卷 2078-2096页

作者： Mehrab Lotfpour Changiz Dehghanian Massoud Emamy Ahmad Bahmani Mehdi malekan Ahmad Saadati Milad Taghizadeh Mohammadreza Shokouhimehr School of Metallurgy and Materials Engineering College of EngineeringUniversity of TehranP.O.Box 11155-4563TehranIran Department of Mater.Sci.Eng. Research Institute of Advanced MaterialsSeoul National UniversitySeoul 08826Republic of Korea

In the present study,a new biodegradable Mg-Zn-Cu magnesium alloy was introduced for biological *** microstructural analysis showed the formation of Mg Zn Cu intermetallics for the Mg-2Zn-0.1Cu alloy and also the Mg(Zn,Cu);compounds for the Mg-2 Zn alloys with higher Cu ***,the hot extrusion was applied for the grain refinement and changing the distribution of *** vitro immersion tests,electrochemical and corroded surface analyses represented the enhancement of corrosion resistance with 0.1 wt.%Cu ***,the extruded alloys demonstrated more corrosion resistance behavior than that of the cast *** considering the improved tensile properties of Mg-2Zn-0.1Cu alloy,this alloy was regarded as the potential candidate for use as the biodegradable magnesium implant.

关键词： Mg alloys Grain refinement Second phases Hot extrusion Biodegradation behavior

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Enhanced oxidation and overheating resistance of the extruded Mg–Zn–Al–Mn magnesium alloy by Calcium addition

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Journal of Magnesium and Alloys 2023年第4期11卷 1276-1291页

作者： Hanieh Yeganeh Ahmad Bahmani Mehrab Lotfpour Mehdi malekan Masoud Emamy Behzad Nayebi Kwang Seon Shin School of Metallurgy and Materials Engineering College of EngineeringUniversity of TehranP.O.Box 11155-4563TehranIran Department of Advanced Materials and Renewable Energies Iranian Research Organization for Science and TechnologyTehranIran Department of Mechanical Engineering University of NevadaRenoRenoNV 89557USA Advanced Research and Technology of Magnesium(ARTofMag)Co. TehranIran Research Institute of Advanced Materials School of Materials Science and EngineeringSeoul National UniversityGwanak-guSeoul 08826Republic of Korea

The effects of Ca addition on the microstructure and oxidation properties of a new Mg alloy were *** oxidation behavior of the alloys was analyzed by thermal analysis and material characterization of the alloys exposed in flame environment;and both electrical and induction ***,the surface layers were characterized using field emission scanning electron microscopy,and X-ray diffraction *** was found that increasing the Ca addition reduces the grain size and increases the fraction of the secondary phases,and enhances the mechanical ***,increasing the Ca contents resulted in the formation of a dense CaO/MgO layer on the surface prohibited the oxygen diffusion and assisted in protection of the substrate against further ***,ignition temperature was increased from 680℃ to 890℃ after addition of the Ca *** mechanical properties and ignition behavior of the current materials was compared with the literature which it showed an excellent combination of the properties in the developed alloys.

关键词： Mg alloys Oxidation properties Ca addition Microstructure Intermetallic phases

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Unveiling the influence of dendrite characteristics on the slip/twinning activity and the strain hardening capacity of Mg-Sn-Li-Zn cast alloys

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Journal of Magnesium and Alloys 2023年第1期11卷 329-347页

作者： MS.Jalali A.Zarei-Hanzaki M.Mosayebi H.R.Abedi M.malekan M.Kahnooji E.Farabi Su-Hyeon Kim Hot Deformation and Thermomechanical Processing Laboratory of High Performance Engineering Materials School of Metallurgy and Materials EngineeringCollege of EngineeringUniversity of TehranTehranIran Materials Science and Engineering Department McMaster University1280 Main Street WestHamiltonON L8S 4L8Canada School of Metallurgy&Materials Engineering Iran University of Science and Technology(IUST)TehranIran Institute for Frontier Materials Deakin UniversityGeelongVictoria 3216Australia Korea Institute of Materials Science(KIMS) 797 ChangwondaeroSeongsanguChangwonGyeongnam 51508Republic of Korea

This work explores the correlation between the characteristics of the cast structure(dendrite growth pattern,dendrite morphology and macro-texture)and strain hardening capacity during high temperature deformation of Mg-5Sn-0.3Li-0 and 3Zn multi-component *** three dimensional(3D)morphology of the dendrite structure demonstrates the transition of the growth directions from,andtoanddue to the addition of *** simultaneous effects of growing tendency and the decrement of dendrite coarsening rate at the solidification interval lead to dendrite morphology transition from the globular-like to the hyper-branch *** morphology transition results in the variation of the solidification macro-texture,which has effectively influenced the dominant deformation mechanisms(slip/twin activity).The higher activity of the slip systems increases the tendency of the dendrite arms for bending along the deformation direction and *** from this,the dendrite holding hyper-branch structure with an average thickness below 20μm are more favorable for *** dendrite fragmentation leads to considerable softening fractions,and as an effective strain compensation mechanism increases the workability of dendritic structure.

关键词： Magnesium alloys Dendrite orientation selection Solidification texture Dendrite fragmentation 3-D tomography analysis Thermomechanical processing

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