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A numerical study on the influence of grain boundary oxides on dwell fatigue crack growth of a nickel-based superalloy

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Journal of Materials Science & Technology 2022年第9期104卷 224-235页

作者： c.Z.Fang h.c.Basoalto M.J.Anderson h.Y.Li S.J.Williams P.Bowen Department of Materials Science and Engineering University of SheffieldMappin StSheffield S13JDUK School of Metallurgy and Materials University of BirminghamEdgbastonBirmingham B152TTUK Institute of Structural Materials Swansea UniversitySwansea SA18ENUK

A theoretical treatment on the oxide-controlled dwell fatigue crack growth of aγ'strengthened nickelbased superalloys is *** particular,this study investigates the influence of an externally applied load and variations in theγ'dispersion on the grain boundary oxide growth kinetics.A dislocation-based viscoplastic constitutive description for high temperature deformation is used to simulate the stress state evolution in the vicinity of a crack at elevated *** viscoplastic model explicitly accounts for multimodalγ'particle size distributions.A multicomponent mass transport formulation is used to simulate the formation/evolution of an oxide wedge ahead of the crack tip,where stress-assisted vacancy diffusion is assumed to *** resulting set of constitutive and mass transport equations have been implemented within a finite element *** of predicted compositional fields across the matrix/oxide interface are compared with experiments and shown to be in good *** indicate that the presence of a fineγ'size distribution has a strong influence on the predicted ow stress of the material and consequently on the relaxation in the vicinity of the crack-tip/oxide *** is shown that a unimodal dispersion leads to reduced oxide growth rates(parabolic behavior)when compared to a bimodal *** conditions for oxide formation are investigated and is associated with the prediction of compressive stresses within the oxide layer just ahead of the crack tip,which become progressively negative as the oxide wedge ***,mechanical equilibrium requirements induce tensile stresses at the tip of the oxide wedge,where failure of the oxide is *** time taken to reach this critical stress for oxide failure has been calculated,from which dwell crack growth rates are computationally *** predicted rates are shown to be in good agreement with available experimental data.

关键词： Nickel based superalloy Dwell crack growth Gamma prime creep Oxidation Dislocation-based modeling Multicomponent diffusion Finite element method

Influences of residual stress and micro-deformation on microstructures and mechanical properties for Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy produced by laser powder bed fusion

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Journal of Materials Science & Technology 2021年第16期75卷 174-183页

作者： c.c.Zhang h.L.Wei T.T.Liu L.Y.Jiang T.Yang W.h.Liao National Joint Engineering Research center of Nc Forming Technology and Equipment School of Mechanical EngineeringNanjing University of Science and TechnologyNanjing 210094China

Laser powder bed fusion(LPBF)yields unique advantages during the fabrication of titanium *** the present work,Ti-6.5 Al-3.5 Mo-1.5 Zr-0.3 Si alloy specimens with excellent mechanical performances were fabricated by *** as-built specimens displayed relatively high strength and ductility under modest volume energy densities(VEDs),whereas they manifested high strength with low ductility under high *** investigate the key reason of this phenomenon,the specimens were designed with two VEDs ranges of 60 J/mm^(3) and 85 J/mm^(3).Special attention was paid to the influences of residual stress and micro-deformation on microstructures and mechanical properties for the first *** results indicated that the residual stresses and relative density of the 60 J/mm^(3) range specimens were higher than that of the 85 J/mm3 range *** multiplication and dislocation movement promoted by the residual stress were hindered by the initialα’phase grain boundary(prior-α’GB),leading to the formation ofα’metastable *** mean tensile strength and elongation of the 60 J/mm^(3) range specimens were 1248.1 MPa and 12.3%,respectively,whereas the corresponding values for the 85 J/mm^(3) range specimens were 1405.3 MPa,5.0%,*** deformation,the strength and ductility of the specimens were first improved by lamellar structures generated from prior-α’phases,and then effectively enhanced by the interaction between the{10–12}twins and ***,pores significantly reduced the ductility;hence,high VED specimens with large twins and numerous large pores increased the strength and reduce the ductility.

关键词： Laser powder bed fusion Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy Residual stress Twin Mechanical properties

DYNAMIc cOMPAcTION OF PURE cOPPER POWDER USING PULSED MAGNETIc FORcE

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Acta Metallurgica Sinica(English Letters) 2007年第4期20卷 277-283页

作者： h.P. Yu c.F. Li National Key Laboratory for Precision hot Processing of Metals Harbin Institute of Technology Harbin 150001 China

The compaction of pure cu powder was carried out through a series of experiments using dynamic magnetic pulse compaction, and the effects of process parameters, such as discharge energy and compacting direction, on the homogeneity and the compaction density of compacted specimens were presented and discussed. The results indicated that the compaction density of specimens increased with the augment of discharge voltage and time. During unidirectional compaction, there was a density gradient along the loading direction in the compacted specimen, and the minimum compaction density was localized to the center of the bottom of the specimen. The larger the aspect ratio of a powder body, the higher the compaction density of the compacted specimen. And high conductivity drivers were beneficial to the increase of the compaction density. The iterative and the double direction compaction were efficient means to manufacture the homogeneous and high-density powder parts.

关键词： magnetic pulse compaction copper powder compaction density electromagnetic forming

Intermediate Energy coulomb Excitation of Neutron-Rich Nuclei

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chinese Physics Letters 2010年第3期27卷 104-107页

作者： Rajiv Kumar Rajesh Kharab h. c. Sharma Department of Applied Sciences Haryana College of Technology and Management Kaithal-136027 India Department of Physics Kurukshetra University Kurukshetra-136119 India

We reinvestigate the collective effects of the retardation as well as the bending on the coulomb excitation cross sections and also on the B（E2） strengths of some neutron-rich isotopes using the intermediate energy coulomb excitation theory. It is found that the B（E2） strengths extracted from the experimental coulomb excitation cross section data get suppressed approximately by 6%. Furthermore, the obtained B（E2） strengths in the energy range 30-100 MeV/A are found to be in better agreement with the corresponding values known from other sources, than those obtained by using the recoil-corrected relativistic coulomb excitation theory.

关键词： Nuclear physics

Exact solution and transient behavior for torsional vibration of functionally graded finite hollow cylinders

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Acta Mechanica Sinica 2009年第4期25卷 555-563页

作者： h. M. Wang c. B. Liu h. J. Ding Department of Mechanics Zhejiang University Department of civil Engineering Zhejiang University

Exact solutions are obtained for transient torsio- nal responses of a finitely long, functionally graded hollow cylinder under three different end conditions, i.e. free-free, free-fixed and fixed-fixed. The cylinder with its external surface fixed is subjected to a dynamic shearing stress at the internal surface. The material properties are assumed to vary in the radial direction in a power law form, while keep invariant in the axial direction. With expansion in the axial direction in terms of trigonometric series, the governing equations for the unknown functions about the radial coordinate r and time t are deduced. By applying the variable substitution technique, the superposition method and the separation of variables consecutively, series-form solutions of the equations are obtained. Natural frequencies and the transient torsional responses are finally discussed for a functionally graded finite hollow cylinder.

关键词： Exact solution Functionally graded material Finite hollow cylinder Transient torsional vibration

Design of a Biomimetic Skin for an Octopus-Inspired Robot - Part Ⅱ： Development of the Skin Artefact

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Journal of Bionic Engineering 2011年第3期8卷 297-304页

作者： Jinping hou Richard h. c. Bonser George Jeronimidis centre for Biomimetics School of Construction Management and Engineering UniversiO~ of Reading Reading RG6 6A Y UK

In order to develop skin artefact for an octopus-inspired robot arm, which is designed to be able to elongate 60% of its original length, silicone nlbber and knitted nylon sheet were selected to manufacture an artificial skin, due to their higher elastic strain and high flexibility. Tensile and scissors cutting tests were conducted to characterise the matrix and reinforcing materials and the skin artefact. Material properties of the individual and the composite materials were compared with the measured properties of real octopus skin presented ill Part I. The Young＇s modulus of the skin should be below 20 MPa and the elastic strain range should be over 60%. The fracture toughness should be at least 0.9 kJ.m 2. Tubes made of the skin artefact filled with liquid were tested to study volume change under deformation. Finite element analysis model was developed to simulate the material and arm structure under tensile loading. Results show that the skin artefact developed has similar mechanical properties as the real octopus skin and satisfies all the design specifications of the OcTOPUS robot.

关键词： octopus skin static tensile test toughness skin artefact nylon/silicone composite

Developing Skin Analogues for a Robotic Octopus

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Journal of Bionic Engineering 2012年第3期9卷 385-390页

作者： Jinping hou Richard h. c. Bonser George Jeronimidis centre for Biomimetics School of Construction Management and Engineering University of Reading Reading RG6 6AY UK School of Engineering and Design Brunel University Uxbridge Middlesex UB8 3PH UK

In order to fabricate a biomimetic skin for an octopus inspired robot, a new process was developed based on mechanical properties measured from real octopus skin. Various knitted nylon textiles were tested and the one of 10-denier nylon was chosen as reinforcement. A combination of Ecoflex 0030 and 0010 silicone rubbers was used as matrix of the composite to obtain the right stiffness for the skin-analogue system. The open mould fabrication process developed allows air bubble to escape easily and the artificial skin produced was thin and waterproof. Material properties of the biomimetic skin were char- acterised using static tensile and instrumented scissors cutting tests. The Young＇s moduli of the artificial skin are 0.08 MPa and 0.13 MPa in the longitudinal and transverse directions, which are much lower than those of the octopus skin. The strength and fracture toughness of the artificial skin, on the other hand are higher than those of real octopus skins. conically-shaped skin prototypes to be used to cover the robotic arm unit were manufactured and tested. The biomimetic skin prototype was stiff enough to maintain it conical shape when filled with water. The driving force for elongation was reduced significantly compared with previous prototypes.

关键词： biomimetic skin artefact octopus robot textile composite

Bifurcation phenomena and control for magnetohydrodynamic flows in a smooth expanded channel

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chinese Physics B 2014年第11期23卷 374-383页

作者： G.c.Layek Mani Shankar Mandal h.A.Khalaf Department of Mathematics The University of Burdwan Department of Mathematics Krishnagar Govt. College KrishnagarNadia 741101India Thi-Qar University Marshes Research Center Thi-QarIraq

This work reports the effects of magnetic field on an electrically conducting fluid with low electrical conductivity flowing in a smooth expanded channel. The governing nonlinear magnetohydrodynamic （MhD） equations in induction- free situations are derived in the framework of MhD approximations and solved numerically using the finite-difference technique. The critical values of Reynolds number （based on upstream mean velocity and channel height） for symmetry breaking bifurcation for a sudden expansion channel （1：4） is about 36, whereas the value in the case of the smooth expansion geometry used in this work is obtained as 298, approximately （non-magnetic case）. The flow of an electrically conducting fluid in the presence of an externally applied constant magnetic field perpendicular to the plane of the flow is reduced significantly depending on the magnetic parameter （M）. It is expansion （1：4） is about 475 for the magnetic parameter M found that the critical value of Reynolds number for smooth = 2. The separating regions developed behind the smooth symmetric expansion are decreased in length for increasing values of the magnetic parameter. The bifurcation diagram is shown for a symmetric smoothly expanding channel. It is noted that the critical values of Reynolds number increase with increasing magnetic field strength.

关键词： weakly electrically conducting fluid flow bifurcation asymmetric flow smooth expansion

Flow of a micropolar fluid in a micro-channel under the action of an alternating electric field: Estimates of flow in bio-fluidic devices

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Journal of hydrodynamics 2015年第3期27卷 350-358页

作者： MISRA J.c. chANDRA S. hERWIG h. centre for healthcare Science and Technology Indian Institute of Engineering Science and Technology Department of Physics Sabang S. K. Mahavidyalaya Vidyasagar University Institute of Thermo-Fluid Dynamics Technische Universitat Hamburg-Harburg

The paper is devoted to a study of the electro-osmotic flow of a micropolar bio-fluid, when the flow takes place between two plates that are in a state of periodic vibrations. considering blood as a micropolar fluid, it is found that the amplitude of oscillation of the microparticles of blood increases when the micropolar effect is pronounced more and more and that a rise in Debyehtickel parameter enhances both the velocity and microrotation gradient. The results provide guidelines for the improvement of design of bio-sensing and micro-fluidic devices. The study leads to the conclusion that electrical double layers formed in the vicinity of the wall can significantly alter the flow dynamics of physiological fluids in micro-bio-fluidic devices.

关键词： microrotation Electro-osmotic flow Debye-hiickel parameter micropolar fluid