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Elastic-plastic behavior of a semicircular frame being pressed against a rigid plane

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Acta Mechanica Sinica 2008年第4期24卷 419-432页

作者： x.W.Zhang J.L.Yang T.x.yu Institute of Solid Mechanics Beihang University Beijing 100083 China Department of Mechanical Engineering Hong Kong University of Science and Technology Kowloon Hong Kong China

As a simplified structural model, a semicircular frame is used to study the crashworthiness behavior of an aircraft fuselage. The quasi-static large elastic-plastic deformation of a semicircular frame in the process of its being pressed against a rigid ground is analyzed. First, based on the linear elastic assumption, the quasi-static large deformation contact process of the frame can be divided into three phases, i.e., point contact, line contact and post-buckling. By means of a shooting method, the relations between the displacement and contact force as well as the distribution of bending moment in the three phases are obtained. Then, by assuming an elastic, perfectly-plastic moment-curvature relationship for the semi-circular frame, the contact process is analyzed in detail to reveal the plastic collapse mechanism, the traveling of plastic hinge and the force-displacement relationship. In order to verify the analysis, a preliminary experiment was conducted, in which two types of half rings with clamped ends were pressed by a rigid plate. In addition, a numerical simulation is also conducted by employing ABAQUS to analyze both rectangular cross-sectional beam and I-beam. Finally, the theoretical predictions are compared with the experimental results and numerical solutions, showing that the elastic-plastic analysis can predict the contact process very well.

关键词： Elastic-plastic·Large deformation ·Semicircular frame Contact ·Traveling hinge

Static and dynamic snap-through behaviour of an elastic spherical shell

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Acta Mechanica Sinica 2012年第3期28卷 695-710页

作者： D. Karagiozova x.-W. Zhang T.-x. yu Department of Mechanical Engineering Hong Kong University of Science and TechnologyClear Water Bay Kowloon Hong Kong China Institute of Mechanics Bulgarian Academy of SciencesAcad. G. Bonchev Street Block 4Sofia 1113 Bulgaria School of Mechantronical Engineering Beijing Institute of Technology100081 Beijing China

The deformation and snap-through behaviour of a thin-walled elastic spherical shell statically compressed on a flat surface or impacted against a fiat surface are studied the- oretically and numerically in order to estimate the influence of the dynamic effects on the response. A table tennis ball is considered as an example of a thin-walled elastic shell. It is shown that the increase of the impact velocity leads to a variation of the deformed shape thus resulting in larger de- formation energy. The increase of the contact force is caused by both the increased contribution of the inertia forces and contribution of the increased deformation energy. The contact force resulted from deformation/inertia of the ball and the shape of the deformed region are calcu- lated by the proposed theoretical models and compared with the results from both the finite element analysis and some previously obtained experimental data. Good agreement is demonstrated.

关键词： Elastic spherical shell Snap-through buckling.Static Dynamic

MECHANICAL BEHAVIOR OF FCC CRYSTAL SIMULATED BY 3-D DISCRETE DISLOCATION DYNAMICS

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Acta Metallurgica Sinica(English Letters) 2008年第2期21卷 94-102页

作者： Y.yu x.x. Pan Y.H. Rong School of Materials Science and Engineering Shanghai Jiaotong University Shanghai 200030 China Institute of Structural Mechanics China Academy of Engineering Physics Mianyang 621900 ChinaManuscript received 31 May 2007

To simulate the mechanical behavior of the FCC crystal with the lower Peierls stress, the stiff property and physical meaning of the differential equation group consisting of dislocation evolution and mechanical state was investigated based on the 3-D discrete dislocation dynamics; the results indicate that the differential equation group is serious stiff, namely the external stress changes more quickly than dislocation evolution. Using the established numerical algorithm, the mechanical behavior of FCC crystal was simulated with the dislocations located in the parallel slip planes, and the effect of strain rate on the dislocation configuration and mechanical behavior, and the sat- uration process of mobile dislocation were discussed. The simulation results indicate that the numerical algorithm can efficiently simulate the dislocation dipole and the low strain rate loading.

关键词： FCC crystal Mechanical behavior Dislocation dynamics Nu-merical simulation

Guided Waves in the Multilayered One-Dimensional Hexagonal Quasi-crystal Plates

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Acta Mechanica Solida Sinica 2021年第1期34卷 91-103页

作者： B.Zhang J.G.yu x.M.Zhang x.H.Wang School of Mechanical and Power Engineering Henan Polytechnic UniversityJiaozuo454003China

Guided waves in the multilayered one-dimensional quasi-crystal plates are,respectively,investigated in the context of the Bak and elasto-hydrodynamic *** curves and phonon and phason displacements are calculated using the Legendre polynomial *** characteristics in the context of these two models are analyzed in *** show that the phonon-phason coupling effects on the first two layers are the same at low frequencies;but,they are more significant on the first layer than those on the second layer at high *** obtained results lay the theoretical basis of guided-wave nondestructive test on multilayered quasi-crystal plates.

关键词： Multilayered structures Quasi-crystal plate Guided wave Phonon-phason coupling effect

A two-scale method for identifying mechanical parameters of composite materials with periodic configuration

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Acta Mechanica Sinica 2006年第6期22卷 581-594页

作者： J.Z. Cui x.G. yu Academy of Mathematics and System Sciences Chinese Academy of Sciences Beijing 10080 China

In this paper, a two-scale method （TSM） is presented for identifying the mechanics parameters such as stiffness and strength of composite materials with small periodic configuration. Firstly, a formulation is briefly given for two-scale analysis （TSA） of the composite materials. And then a two-scale computation formulation of strains and stresses is developed by displacement solution with orthotropic material coefficients for three kinds of such composites structures, i.e., the tension column with a square cross section, the bending cantilever with a rectangular cross section and the torsion column with a circle cross section. The strength formulas for the three kinds of structures are derived and the TSM procedure is discussed. Finally the numerical results of stiffness and strength are presented and compared with experimental data. It shows that the TSM method in this paper is feasible and valid for predicting both the stiffness and the strength of the composite materials with periodic configuration.

关键词： Two-scale method Stiffness Strength Composite materials Small periodic configuration

Deformation kinking and highly localized nanocrystallization in metastableβ-Ti alloys using cold forging

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Journal of Materials Science & Technology 2022年第25期120卷 53-64页

作者： Keer Li W.Chen G.x.yu J.Y.Zhang S.W.xin J.x.Liu x.x.Wang J.Sun State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China Northwest Institute for Nonferrous Metal Research Xi’an 710016China Baoji Titanium Industry Co. Ltd.Baoji 721014China

Deformation kinking as an uncommon plastic deformation mechanism has been reported in several materials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so *** this study,the issue was systematically investigated by utilizing cold forging to impose severe plastic deformation(SPD)on Ti-11 V metastableβ-Ti *** is found that the formation of kink bands experiences dislocation gliding,pre-kinking and the ripening of pre-kinks in *** kink bands are subsequently thickened through the coalescence of multiple kink bands in a manner of high *** dislocation slip is developed as a dominant deformation mechanism when deformation kinking is *** resulting grain refinement involves transverse breakdown and longitudinal splitting of dislocation walls and cells,which fragment kink bands into smallβ-*** refinement of theβ-blocks is still governed by dislocation activities,and finally nanograins with a diameter of~15 nm are produced at a large strain of ***,it is revealed that nanocrystallization is highly localized inside kink bands while the outer microstructure maintains original coarse *** localized refinement characterization is ascribed to the intrinsic soft nature of kink bands,shown as low hardness in nanoindentation *** intrinsic softening of kink bands is uncovered to originate from the inner degraded dislocation density evidenced by both experimental measurement and theoretical *** findings enrich fundamental understanding of deformation kinking,and shed some light on exploring the deformation accommodation mechanisms for metal materials at large strains.

关键词： Metastableβ-Ti alloys Deformation kinking Microstructural evolution Grain refinement Dislocations

Production of Nanometer Powders with an Electrohydrodynamic Technique

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Journal of Materials Science & Technology 1997年第3期13卷 211-214页

作者： yu, xF Hu, ZQ Liu, x Cheng, LZ NORTHEASTERN UNIV SHENYANG 110006 PEOPLES R CHINA

The principle of producing nanometer powders with the electrohydrodynamic technique and the apparatus were described. The effects of the geometry and size of the cathode and anode. and the applied voltage on the emitted current and the mean size of the nanometer powders were *** results show that with the decreasing in the diameter of the cylindrical cathode and in the calibre of the spiral cathode, the mean size of the nanometer powders decreases. The effect of the calibre of the spiral cathode is more remarkable. In addition, the mean size of the nanometer powders decreases with decrease in the internal and external diameter of the anode and the increase in the applied voltage.

关键词： Nanotechnology

Fracture of Aramid Fiber/Epoxy Resin Micro Composites

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Journal of Materials Science & Technology 1995年第4期11卷 260-264页

作者： WANG, x ZHANG, Cx JIN, SJ yu, YZ Inst of Chemistry Chinese Acad of Sciences Beijing China

Kevlar-49 fiber was modified through cold air plasma treatment and plasma grafting with acrylic monomers. Fracture of aramid fiber/epoxy resin micro composites has been studied by means of single fiber pull-out test. Tow types of pull-out curves are correlated with the different failure modes. A polyacrylic acid-co-ethyl acrylate graft layer can improve the adhesion and protect the fiber from damage caused by interfacial stresses.

关键词： Fiber reinforced plastics

4D spinless topological insulator in a periodic electric circuit

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National Science Review 2020年第8期7卷 1288-1295页

作者： Rui yu Y.x.Zhao Andreas P.Schnyder School of Physics and Technology Wuhan University National Laboratory of Solid State Microstructures and Department of Physics Nanjing University Collaborative Innovation Center of Advanced Microstructures Nanjing University Max-Planck-Institute for Solid State Research

According to the mathematical classification of topological band structures, there exist a number of fascinating topological states in dimensions larger than three with exotic boundary phenomena and interesting topological responses. While these topological states are not accessible in condensed matter systems, recent works have shown that synthetic systems, such as photonic crystals or electric circuits, can realize higher-dimensional band structures. Here, we argue that, because of its symmetry properties, the 4D spinless topological insulator is particularly well suited for implementation in these synthetic systems. We explicitly construct a 2D electric circuit lattice, whose resonance frequency spectrum simulates the 4D spinless topological insulator. We perform detailed numerical calculations of the circuit lattice and show that the resonance frequency spectrum exhibits pairs of 3D Weyl boundary states, a hallmark of the nontrivial topology. These pairs of 3D Weyl states with the same chirality are protected by classical time-reversal symmetry that squares to +1, which is inherent in the proposed circuit lattice. We also discuss how the simulated 4D topological band structure can be observed in experiments.

关键词： topological circuit 4D topological states 4D topological Hall effect second Chern number Weyl states