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Effects of grain size and Al addition on the activation volume and strain-rate sensitivity of CoCrFeMnNi high-entropy alloy

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Journal of Materials Science & Technology 2023年第12期143卷 242-252页

作者： h.T.Jeong w.J.Kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul121-791Republic of Korea

The activation volume(V∗)and strain-rate sensitivity exponent(m)of CoCrFeMnNi and Al_(0.5)CoCrFeMnNi high entropy alloys(hEAs)with various grain sizes(ranging between 2.4 and 356μm)were measured at different strain rates and strain levels at room *** the strain rate decreased,the plastic strain decreased,and the grain size increased,V∗*** enhanced solid-solution strengthening by addition of aluminum decreased V∗.The hassen plot was modified to capture the grain-size depen-dence of V∗by considering the grain-size dependence of the dislocation *** the plastic strain increased,the strain rate decreased,and the grain size decreased,m *** behavior of m could be quantitatively predicted by using equations derived for the grain-size-dependent V∗and flow *** difference in the grain-size dependence of m between conventional face centered cubic(FCC)metals and FCC hEAs over the nanograin size range could not be explained in terms of a relatively large hall-Petch slope of the FCC hEAs compared with that of the FCC conventional metals,but was explainable in terms of a substantially higher probability of activation of grain-boundary diffusion-controlled grain-boundary-sliding mechanism at nanograin sizes in the FCC conventional metals than in the FCC hEAs.

关键词： Grain size high entropy alloys Activation volume Strain-rate sensitivity Solid solution

A novel approach to determine residual stress field during FSw of AZ91 Mg alloy using combined smoothed particle hydrodynamics/neuro-fuzzy computations and ultrasonic testing

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Journal of Magnesium and Alloys 2021年第4期9卷 1311-1335页

作者： A.r.Eivani h.Vafaeenezhad h.r.Jafarian J.Zhou School of metallurgy and materials engineering iran university of science and technology^nartnaktehraniran department of biomechanical engineering delft university of technologymekehveg 22628 cd delftthe netherlands

The faults in welding design and process every so often yield defective parts during friction stir welding(FSw).The development of numerical approaches including the finite element method(FEM)provides a way to draw a process paradigm before any physical *** is not practical to simulate all possible designs to identify the optimal FSw practice due to the inefficiency associated with concurrent modeling of material flow and heat dissipation throughout the *** study intends to develop a computational workflow based on the mesh-free FEM framework named smoothed particle hydrodynamics(SPh)which was integrated with adaptive neuro-fiizzy inference system(ANFIS)to evaluate the residual stress in the FSw *** integrated SPh and ANFIS methodology was established and the well-trained ANIS was then used to predict how the FSw process depends on its *** verify the SPh calculation,an itemized FSw case was performed on AZ91 Mg alloy and the induced residual stress was measured by ultrasonic *** suggested methodology can efficiently predict the residual stress distribution throughout friction stir welding of AZ91 alloy.

关键词： Friction stir welding(FSw) Smoothed particle hydrodynamics(SPh) Adaptive neuro-fuzzy inference system(ANFIS) Ultrasonic residual stress

An Iterative Pose Estimation Algorithm Based on Epipolar Geometry with Application to Multi-Target Tracking

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IEEE/CAA Journal of Automatica Sinica 2020年第4期7卷 942-953页

作者： Jacob h.white randal w.Beard the Brigham Young University ProvoUtah 84058 USA

This paper introduces a new algorithm for estimating the relative pose of a moving camera using consecutive frames of a video sequence. State-of-the-art algorithms for calculating the relative pose between two images use matching features to estimate the essential matrix. The essential matrix is then decomposed into the relative rotation and normalized translation between frames. To be robust to noise and feature match outliers, these methods generate a large number of essential matrix hypotheses from randomly selected minimal subsets of feature pairs, and then score these hypotheses on all feature pairs. Alternatively, the algorithm introduced in this paper calculates relative pose hypotheses by directly optimizing the rotation and normalized translation between frames, rather than calculating the essential matrix and then performing the decomposition. The resulting algorithm improves computation time by an order of magnitude. If an inertial measurement unit(IMU) is available, it is used to seed the optimizer, and in addition, we reuse the best hypothesis at each iteration to seed the optimizer thereby reducing the number of relative pose hypotheses that must be generated and scored. These advantages greatly speed up performance and enable the algorithm to run in real-time on low cost embedded hardware. we show application of our algorithm to visual multi-target tracking(MTT) in the presence of parallax and demonstrate its real-time performance on a 640 × 480 video sequence captured on a UAV. Video results are available at https://***/hh K-p2 h XNn U.

关键词： Aerial robotics epipolar geometry multi-target tracking pose estimation unmanned aircraft systems vision-based flight

Microstructure tailoring of Al_(0.5)CoCrFeMnNi to achieve high strength and high uniform strain using severe plastic deformation and an annealing treatment

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Journal of Materials Science & Technology 2021年第12期71卷 228-240页

作者： h.T.Jeong w.J.Kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

Ultrafine-grained alloys fabricated by severe plastic deformation(SPD)have high strength but often poor uniform *** via high-ratio differential speed rolling(hrDSr)followed by an annealing treatment was applied to Al_(0.5)CoCrFeMnNi to design the microstructure from which both high strength and high uniform strain can be *** optimized microstructure was composed of an ultrafine-grained FCC matrix(1.7-2μm)with a high fraction of high-angle grain boundaries(61%-66%)and ultrafine BCC particles(with a size of 0.6-1μm and a volume fraction of8%-9.3%)distributed uniformly at the grain boundaries of the FCC *** the severely plastically deformed microstructure,the nucleation kinetics of the BCC phase was *** static recrystallization(CSrX)took place during the annealing process at 1273 *** of the BCC phase particles occurring concurrently with CSrX effectively retarded the grain growth of the FCC *** precipitation of the hard and brittleσphase was,however,*** annealed sample processed by hrDSr with the optimized microstructure exhibited a high tensile strength of over 1 GPa with a good uniform elongation of 14%-20%.These tensile properties are comparable to those of transformation-induced plasticity *** mechanisms of the severely plastically deformed alloy before and after annealing were identified,and each strengthening mechanism contribution was *** calculated results matched well with the experimental results.

关键词： high entropy alloys Severe plastic deformation Uniform ductility high strength Dual phase Annealing

Mechanistic investigation on Ce addition in tuning recrystallization behavior and mechanical property of Mg alloy

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Journal of Materials Science & Technology 2023年第1期132卷 1-17页

作者： J.r.Li D.S.Xie Z.r.Zeng B.Song h.B.Xie r.S.Pei h.C.Pan Y.P.ren G.w.Qin Key Laboratory for Anisotropy and Texture of Materials(Ministry of Education) College of Materials Science and EngineeringNortheastern UniversityShenyang110819China College of Engineering and Computer Science Australian National UniversityACT 2601Australia School of Materials and Energy Southwest UniversityChongqing 400715China Institute for Physical Metallurgy and Materials Physics RWTH Aachen UniversityAachen 52062Germany

Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility syn-ergy in Mg *** of bimodal grain is closely related to the dynamic and/or static recrystal-lization process,which has not been fully understood in the typical Mg-rE based *** this work,it is claimed for the first time that the minor Ce addition(∼0.3 wt%)into Mg matrix significantly pro-motes the pyramidaland non-basaldislocations at the early stage of extrusion,which con-sequently enhances the formation of sub-grain boundaries via the movement and recovery of pyramidal II-type*** this stage,fine sub-grain lamellae are widely observed predominantly due to the low migration rate of sub-grain boundary caused by the limited mobility of*** the later stage,the sub-grains continuously transform into dynamic recrystallized(DrXed)grains that have10¯10Taylor axis and also strong fiber texture,indicating substantial activation of pyramidal II-type*** low mobility ofdislocations,accompanied with the solute drag from grain boundary(GB)segregation and pinning from nano-phases,cause a sluggish DrX process and thus a bimodal microstructure with ultra-fined DrXed grains,∼0.51μ*** resultant texture hardening and grain refinement hardening effects,originated from bimodal microstructure,result in a yield strength of∼352 MPa,which is exceptional in Mg-Ce dilute *** work clarifies the critical role of Ce addition in tuning recrystallization behavior and mechanical property of magnesium,and can also shed light on designing the other high-performance Mg alloys.

关键词： Mg alloys recrystallization behavior Mechanical property Pyramidal dislocation Thermal stability

Nucleon transition form factors at JLab:status and outlook

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Chinese Physics C 2009年第12期33卷 1216-1221页

作者： r. w. Gothe University of South Carolina Columbia SC 29208 USA

The measurements of exclusive single-meson and double-pion electro-production cross sections off the proton to study nucleon resonances will be extended to higher momentum transfers with the CLAS12 detector and the energy upgraded CEBAF beam. Based on new theoretical developments to extract and interpret the electromagnetic transition form factors and on the experience gained from the most recent results, the newly formed collaboration of experimentalists and theorists shall enable us to provide unprecedented high- precision data, high-quality analyses, and state-of-the-art model and QCD based calculations in a Q2 domain up to 10 GeV2. For the first time nucleon resonance structures will be studied at still unexplored distance scales, where the dressed quark contributions are the dominating degrees of freedom and their strong interaction is responsible for the ground and excited nucleon state formation. These studies also open up a promising opportunity to understand the origin of more than 98% of the nucleon mass that is created by strong fields predominantly at these distance scales by dressing the current quarks.

关键词： baryon structure strong degrees of freedom

Control over hysteresis curves and thresholds of optical bistability in different semiconductor double quantum wells

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Chinese Physics B 2015年第8期24卷 373-380页

作者： hamedi h r Mehmannavaz M r Afshari hadi Institute of Theoretical Physics and Astronomy Vilnius University Young researchers and Elite Club Mashhad Branch Islamic Azad University research Institute for Applied Physics University of Tabriz

The effects of optical field on the phenomenon of optical bistability(OB) are investigated in a K-type semiconductor double quantum well(SDQw) under various parametric conditions. It is shown that the OB threshold can be manipulated by increasing the intensity of coupling field. The dependence of the shift of OB hysteresis curve on probe wavelength detuning is then explored. In order to demonstrate controllability of the OB in this SDQw, we compare the OB features of three different configurations which could arise in this SDQw scheme, i.e., K-type, Y-type, and inverted Y-type systems. The controllability of this semiconductor nanostructure medium makes the presented OB scheme more valuable for applications in all-optical switches, information storage, and logic circuits of all optical information processing.

关键词： optical bistability semiconductor double quantum wells K-type Y-type and inverted Y-type schemes OB threshold intensity

Effect of electrical discharge in water on concentration of nitrate solution

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Chinese Physics B 2017年第2期26卷 305-312页

作者： F Sohbatzadeh h Bagheri r Safari Department of Atomic and Molecular Physics Faculty of Basic Sciences University of Mazandaran Babolsar lra

In this work, the effect of electrical discharge on nitrate concentration is considered in aqueous solution. The atmospheric pressure plasma was produced by a high-voltage power supply at 27 k hz using pin-to-pin configuration. Air, argon,and argon/methane mixture were used to study the working gas effect. UV-VIS spectroscopy and ion chromatography were used to analyze the effect of the electrical discharge on nitrate concentration in deionized water. Optical emission spectroscopy（OES） was applied to diagnose active species inside and on the surface of the deionized water solution. The results of the present work showed that the atmospheric pressure electric discharge with air increases nitrate concentration while it remains constant using argon and argon/methane electrical discharges. It was also revealed that in the presence of air, the electrical discharge reduces p h, acidifying the solution and increasing solution conductivity due to production of extra nitrate ions. On the other hand, argon electrical discharge increases p h and conductivity due to production of Ohion in water.

关键词： electric discharge nitrate solution optical spectroscopy

robust nonlinear control for nuclear reactors using sliding mode observer to estimate the xenon concentration

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Nuclear Science and Techniques 2016年第2期27卷 106-114页

作者： G.r.Ansarifar h.r.Akhavan Department of Nuclear Engineering Faculty of Advanced Sciences and Technologies University of Isfahan

This paper presents findings on the sliding mode controller for a nuclear reactor. One of the important operations in nuclear power plants is load following. In this paper, a sliding mode control system, which is a robust nonlinear controller, is designed to control the pressurizedwater reactor power. The reactor core is simulated based on the point kinetics equations and six delayed neutron groups. Considering neutron absorber poisons and regarding the limitations of the xenon concentration measurement, a sliding mode observer is designed to estimate its value, and finally, a sliding mode control based on the sliding mode observer is presented to control the core power of reactor. The stability analysis is given by means Lyapunov approach; thus, the control system is guaranteed to be stable within a large range. The employed method is easy to implement in practical applications, and moreover,the sliding mode control exhibits the desired dynamic properties during the entire output-tracking process independent of perturbations. Simulation results are presented to demonstrate the effectiveness of the proposed observerbased controller in terms of performance, robustness and stability.

关键词：鲁棒非线性控制滑模观测器核反应堆估计氙气气浓度非线性鲁棒控制器滑模控制系统