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Superplastic behavior of a fine-grained Mg-Gd-Y-Ag alloy processed by equal channel angular pressing

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Journal of Magnesium and Alloys 2023年第10期11卷 3815-3828页

作者： A.rezaei r.Mahmudi r.E.Logé School of Metallurgical and Materials Engineering College of EngineeringUniversity of TehranTehran 14395-515Iran Laboratory of Thermomechanical Metallurgy-PX Group Chair Ecole Polytechnique Fédérale de Lausanne(EPFL)CH-2002 NeuchâtelSwitzerland

An extruded Mg-6Gd-3Y-1.5Ag(wt%) alloy was processed by 6 passes of equal channel angular pressing(ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction(EBSD) analysis showed a fully recrystallized microstructure for the extruded alloy with a mean grain size of 8.6 μm. The microstructure of the ECAP-processed alloy was uniformly refined through dynamic recrystallization(DrX). This microstructure contained fine grains with an average size of 1.3 μm, a high fraction of high angle grain boundaries(HAGBs), and nano-sized Mg_(5)Gd-type particles at the boundaries of the DrXed grains, detected by transmission electron microscopy(TEM). High-temperature shear punch testing(SPT) was used to evaluate the superplastic behavior of both the extruded and ECAP-processed alloys by measuring the strain rate sensitivity(SrS) index(m-value). While the highest m-value for the extruded alloy was measured to be 0.24 at 673 K, the ECAP-processed alloy exhibited much higher m-values of 0.41 and 0.52 at 598 and 623 K, respectively,delineating the occurrence of superplastic flow. Based on the calculated average activation energy of 118 kJ mol^(-1) and m-values close to 0.5, the deformation mechanism for superplastic flow at the temperatures of 598 and 623 K for the ECAP-processed alloys was recognized to be grain boundary sliding(GBS) assisted by grain boundary diffusion.

关键词： Mg-Gd-Y alloys Equal channel angular pressing Superplasticity Strain rate sensitivity Grain boundary sliding

Design concepts of an aircraft wing： composite and morphing airfoil with auxetic structures

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Frontiers of Structural and Civil Engineering 2016年第4期10卷 394-408页

作者： P r BUDArAPU Sudhir Sastry Y B r NATArAJAN Department of Aerospace Engineering Indian Institute of Science Bangalore 560 012 India Department of Aeronautical Engineering College of Engineering Defence University Ethiopia Department of Aeronautical Engineering Institute of Aeronautical Engineering Hyderabad India

This paper is categorized into two parts. （1） A frame work to design the aircraft wing structure and （2） analysis ofa morphing airfoil with auxetic structure. The developed design frame work in the first part is used to arrive at the sizes of the various components of an aircraft wing structure. The strength based design is adopted, where the design loads are extracted from the aerodynamic loads. The aerodynamic loads acting on a wing structure are converted to equivalent distributed loads, which are further converted point loads to arrive at the shear forces, bending and twisting moments along the wing span. Based on the estimated shear forces, bending and twisting moments, the strength based design is employed to estimate the sizes of various sections of a composite wing structure. A three dimensional numerical model of the composite wing structure has been developed and analyzed for the extreme load conditions. Glass fiber reinforced plastic material is used in the numerical analysis. The estimated natural frequencies are observed to be in the acceptable limits. Furthermore, the discussed design principles in the first part are extended to the design of a morphing airfoil with auxetic structure. The advantages of the morphing airfoil with auxetic structure are （i） larger displacement with limited straining of the components and （ii） unique deformation characteristics, which produce a theoretical in-plane Poisson＇s ratio of -1. Aluminum Alloy AL6061-T651 is considered in the design of all the structural elements. The compliance characteristics of the airfoil are investigated through a numerical model. The numerical results are observed to be in close agreement with the experimental results in the literature.

关键词： wing design aerodynamic loads morphing airfoil auxetic structures negative Poisson's ratio

Activator-assisted electroless deposition of copper nanostructured films

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International Journal of Minerals,Metallurgy and Materials 2014年第2期21卷 196-203页

作者： Varsha r. Mehto r. K. Pandey Department of Physics Barkatullah University NIIT University

This paper showed simple and effective synthesis of copper nanoparticles within controlled diameter using direct electroless deposition on glass substrates, following the sensitization and activation steps. Electroless-deposited metals, such as Cu, Co, Ni, and Ag, and their alloys had many advantages in micro- and nanotechnologies. The structural, morphological, and optical properties of copper deposits were characterized using X-ray diffraction （XrD）, atomic force microscopy （AFM）, and UV-Vis spectroscopy. The structural data was further analyzed using the rietveld refinement program. Structural studies reveal that the deposited copper prefers a （111） orientation. AFM studies suggest the deposited materials form compact, uniform, and nanocrystalline phases with a high tendency to self-organize. The data show that the particle size can be controlled by controlling the activator concentration. The absorption spectra of the as-deposited copper nanoparticles reveal that the plasmonic peak broadens and exhibits a blue shift with decreasing particle size.

关键词： nanostructured materials thin films copper electroless plating deposition

Analysis of surface roughness of rock dust reinforced AA6061-Mg matrix composite in turning

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Journal of Magnesium and Alloys 2021年第5期9卷 1686-1693页

作者： r.Balachandhar r.Balasundaram M.ravichandran Department of Mechanical Engineering Pavender Barathidasan College of Engineering and TechnologyTiruchirappalli620024Tamil NaduIndia Department of Mechanical Engineering K.Ramakrishnan College of EngineeringTiruchirappalli621112Tamil NaduIndia Department of Mechanical Engineering SRM Institute of Science and TechnologyTiruchirappalli Campus621105Tamil NaduIndia

This work,examines the Surface roughness(Sr)of composite consisting Aluminium alloy(AA6061),Magnesium and rock dust during turning *** study the performance,three different test specimens with different constituents of Al 6061-T6,AZ31 and rock dust were prepared by stir casting *** experiments were carried out using MTAB Siemens-CNC *** input parameters for machining are speed,depth of cut&feed and output response is surface roughness For each test specimen,there are 15 turning operations were performed using Box-Ben hen Design *** analyze the process parameters for Sr,the models of ANOVA and Decision Tree(DT)algorithms were *** algorithms are confirmed that,speed is the most significant factor for *** addition of AZ 31 with 1%and rock dust of 2%in AA6061 produced better surface *** models of linear regression,multilayer perception and support vector regression from data science were formulated to find the relationship between *** these models multi layer perception produced minimum root mean square error.

关键词： Composite Turning Surface roughness Anova Decision tree regression

Kinematic analysis of flexible bipedal robotic systems

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Applied Mathematics and Mechanics(English Edition) 2024年第5期45卷 795-818页

作者： r.FAZEL A.M.SHAFEI S.r.NEKOO Department of Mechanical Engineering Shahid Bahonar University of KermanKerman ***Iran Departamento de Ingenieria de Sistemas y Automatica Escuela Técnica Superior de IngenieriaUniversidad de SevillaSeville 41092Spain

In spite of its intrinsic complexities,the passive gait of bipedal robots on a sloping ramp is a subject of interest for numerous *** distinguishes the present research from similar works is the consideration of flexibility in the constituent links of this type of robotic *** is not a far-fetched assumption because in the transient(impact)phase,due to the impulsive forces which are applied to the system,the likelihood of exciting the vibration modes increases ***,the human leg bones that are involved in walking are supported by viscoelastic muscles and ***,for achieving more exact results,it is essential to model the robot links with viscoelastic *** this end,the Gibbs-Appell formulation and Newton's kinematic impact law are used to derive the most general form of the system's dynamic equations in the swing and transient phases of *** most important issue in the passive walking motion of bipedal robots is the determination of the initial robot configuration with which the system could accomplish a periodic and stable gait solely under the effect of gravitational *** extremely unstable nature of the system studied in this paper and the vibrations caused by the impulsive forces induced by the impact of robot feet with the inclined surface are some of the very serious challenges encountered for achieving the above-mentioned *** overcome such challenges,an innovative method that uses a combination of the linearized equations of motion in the swing phase and the algebraic motion equations in the transition phase is presented in this paper to obtain an eigenvalue *** solving this problem,the suitable initial conditions that are necessary for the passive gait of this bipedal robot on a sloping surface are *** effects of the characteristic parameters of elastic links including the modulus of elasticity and the Kelvin-Voigt coefficient on the walking stability of this type of

关键词： bipedal robot flexible link swing phase transient phase eigenvalue problem Kelvin-Voigt coefficient

Experimental investigation and numerical simulation of plastic flow behavior during forward-backward-radial extrusion process

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Progress in Natural Science:Materials International 2016年第6期26卷 650-656页

作者： A.Farhoumand r.Ebrahimi Department of Materials Science and Engineering School of Engineering Shiraz University

Finite element method was employed to investigate the effect of process parameters of plastic deformation behavior in Forward-Backward-radial Extrusion(FBrE) process. The result of an axisymmetric model shows that the friction between die components and the sample has a substantial effect on the material flow *** strain heterogeneity index(SHI) slightly decreases with an increase in friction, large portion of the sample experiences significant strain heterogeneity. Increasing the friction factor also localizes the strain heterogeneity effect in the backward section, and spread the effect in the forward section. Decreasing the friction in the FBrE process can reduce the amount of the strain heterogeneity in the product while decreases the required punch force substantially. Furthermore, an increase in gap thickness increases the deformation in the area close to the lower punch at the expense of the area in the vicinity of the upper punch. The numerical simulation has a good agreement with the experimental results which confirms the accuracy of the proposed finite element model.

关键词： Finite element analysis Extrusion Forming Plastic deformation Strain heterogeneity

A study of local amplification effect of soil layers on ground motion in the Kathmandu Valley using microtremor analysis

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Earthquake Engineering and Engineering Vibration 2012年第2期11卷 257-268页

作者： Paudyal Y.r. Yatabe r. Bhandary N.P. Dahal r.K. Geo-disaster research Laboratory Graduate School of Science and EngineeringEhime UniversityEhimeMatsuyamaJapan

Past researchers have anticipated the occurrence of a great earthquake in the central Himalayas in the near *** may cause serious damage in the Kathmandu Valley,which sits on an ancient lake bed zone,with lacustrine sediments of more than 500 m *** this study,the predominant frequency of ground motion is evaluated using the Horizontal-to-Vertical (H/V) spectral ratio technique and recordings of ambient *** results of the H/V ratio show two peaks in about 20 percent of the locations,which are distributed mainly in and around the center and northern part of the Kathmandu *** predominant frequencies vary from 0.5 Hz to 8.9 Hz in the study area,whereas the second resonance fiequency varies from 4 Hz to 6 Hz in the center and northern part of the *** indicates that the center and northern part of the valley have a wide range of resonance frequency due to two levels of impedance contrast- one may be from the surface layer and the other may be from the layer *** two levels of resonance indicate the importance of considering the effects of surface and lower layers during the planning and designing of infrastructures in the Kathmandu Valley.

关键词： microtremor predominant frequency resonance Kathmandu Valley

Warmer springs, laying date and clutch size of tree sparrows Passer montanus in Croatia

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Current Zoology 2011年第3期57卷 414-418页

作者： Z. DOLENEC r DOLENEC A.r MDLLEr Department of Zoology Faculty of Science University of Zagreb Rooseveltov trg 6 HR- 10000 Zagreb Croatia High School Oroslavje Ljudevita Gaja 1 HR-49243 Oroslavje Croatia Laboratorie d'Ecologie Syst6matique et Evolution CNRS UMR 8079 Universit6 Paris-Sud 362 F-91405 Orsay Cedex France

Global surface air temperatures increased during the past 100 years. Many long-term studies of birds have reported a climatic influence on breeding performance. We analysed long-term changes in first laying date and clutch size for first clutches of sedentary, hole-nesting and socially monogamous tree sparrows Passer montanus during 1980-2009 in northwestern Croatia. Laying date advanced and spring temperature increased significantly during the study. Date of laying was significantly correlated with mean air spring temperature and advanced by 8.6 days during the 30 years period. Laying date was delayed in extremely cold, but not in extremely warm springs compared to years with normal temperatures. These results suggest that current climate change including extreme change does not have negative effects on timing of laying or clutch size. In contrast to laying date, clutch size did not vary systematically during the study period or with mean spring air temperature changes [Current Zoology 57 （3）： 414-418, 2011].

关键词： Climate change Clutch size Laying date Passer montanus Tree sparrow

Transient Thermal Management Comparison of a Microprocessor Using PCMs in Various Configurations

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Journal of Thermal Science 2011年第6期20卷 516-520页

作者： Thenmozhi r Sharmeela C Natarajan P Velraj r Ganthipathy Tulsis' Engineering College AUIndia Anna University ChennaiIndia Bharathidasan Engineering college AUIndia

There has been a strong interest in the use of Phase Change Materials (PCMs) for the transient thermal abatement of high powered *** paper presents a set of transient computational analysis for selected IC packages with the purpose of calibrating the merits of PCM in different *** transient analysis of high powered microprocessors with heat sinks was performed as a benchmark for comparison with the same microprocessors fitted with PCM in the following configurations:a) PCM imbedded into the finned region of the heat sink,b) PCM mounted between the microprocessor and heat sink,c) sealed PCM underfill to the microprocessor and d) PCM fitted to the underside of the printed circuit board directly beneath the *** analysis was performed using a commercial CFD tool together with an approximation to the phase change mechanism using the slope *** indicate the merit of each configuration.

关键词： Phase Change Materials CFD Thermal Management Transient Latent heat