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Propagation behavior of elastic waves in one-dimensional piezoelectric/piezomagnetic phononic crystal with line defects

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Acta Mechanica Sinica 2014年第5期30卷 703-713页

作者： Y.Pang F.-Y.Jiao J.-x.liu Department of Engineering Mechanics Shijiazhuang Tie Dao University School of Mathematics and Physics University of Science and Technology Beijing

Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the re- placement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volume fraction of the defect layers, the type of incident waves, the location of defect layer and the number of structural layers are discussed in detail. Numerical results indicate that defect modes are the most obvious when the defect layers are inserted in the middle of the perfect PCs; the types of incidence wave and material properties of the defect layers have important effects on the numbers, the location of frequencies and the peaks of defect modes, and the defect modes are strongly de- pendent on volume fraction of the defect layers. We hope this paper will be found useful for the design of PE/PM acoustic filters or acoustic transducer with PCs structures.

关键词： 1D phononic crystal Piezoelectric/piezomag- netic. Elastic wave Line defect Stiffness matrix method

In-situ synchrotron high energy x-ray diffraction study on the internal strain evolution of D019-α2 phase during high-temperature compression and subsequent annealing in a TiAl alloy

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Journal of Materials Science & Technology 2023年第32期163卷 212-222页

作者： x.liu L.Song A.Stark F.Pyczak T.B.Zhang State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Innovation Center NPU Chongqing Northwestern Polytechnical UniversityChongqing 400000China Institute of Materials Physics Helmholtz-Zentrum HereonMax Planck-Str.1Geesthacht 21502Germany

The residual stress in the D019-α2 phase is known to be significantly higher than that in the L10-γphase in TiAl alloys after deformation due to the poor plasticity and strong mechanical anisotropy of theα2 ***,the internal stress accumulation and relaxation in theα2 phase during high-temperature deformation and annealing are scarcely *** this study,for the first time,the internal strain evolution and load partitioning between theα2 andγphases at high temperatures are characterized by in-situ synchrotron high energy x-ray diffraction(HExRD)*** plastic deformation is at least initiated at a stress of roughly 200 MPa in theγphase and 775 MPa in theα2 *** intergranular strains in theα2 phase are generated by the onset of dislocation glide in theγphase,and accentuated with the accumulated dislocations and the ensuing twinning *** unloading,great intergranular strains are preserved in theα2 phase constrained by the heavily plastically deformedγ*** subsequent heating from 400 to 1000℃,the internal strains in theα2 phase are almost fully relaxed by substantial dislocation annihilation and rearrangement in theγ*** annealing at 800℃,the internal strain relaxation is rapid in the initial 10 min,whereas considerably retarded *** extent of relaxation after holding at 800℃for 1 h is equivalent to that of heating in an effective temperature range of 680-880℃for 10 *** in-situ lattice strain measurements with various thermal relaxation schemes provide guidance for the stress relief annealing of TiAl components.

关键词： TiAl alloys Synchrotron radiation Intergranular strain Stress relaxation

Phase-field modeling for anisotropic ductile damage of magnesium alloys at finite deformations

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Journal of Magnesium and Alloys 2024年第7期12卷 2967-2984页

作者： C.xie x.K.He x.liu J.H.Ye J.B.Chen Faculty of Mechanical Engineering and Mechanics Ningbo UniversityNingbo 315211PR China Key Laboratory of High Temperature Wear Resistant Materials Preparation Technology of Hunan Province Hunan University of Science and TechnologyXiangtan 411201PR China

The damage anisotropy of an extruded ZK60 Mg alloy is characterized using tensile tests and scanning electronic *** accumulation of anisotropic deformations leads to the great differences of the dimple evolution and strains at fracture along different loading *** introduce the anisotropic deformation information into the damage constitutive relationship,a thermodynamically consistent phase-field model of ductile damage fully coupled with elastoplastic finite deformations is developed in this *** the user-defined constitutive relationship and displacement-temperature coupling element,the finite element simulations are *** results show that:(1)ZK60 Mg alloys presents clear R-value difference in 0°,45°,and 90°tests of intact *** 45°test possesses the greatest R-value(1.50)and the greatest strain at fracture,however,the R-value for 0°is less than 1,indicating the thinning is preferential.(2)The higher ultimate stress leads to a larger average dimension of the dimples,whereas the higher density correlates with a larger elongation ratio at the *** disappearance of the stress-bearing area indicates that the phase-field assumption on stress degradation is completely compatible with the dimple analysis on fractography.(3)The simulation results of the stress-strain relationships and damage paths correlate well with the experimental ductile damage of magnesium alloys at 200◦*** errors are basically attributed to the modeling parameters and finite element iteration *** proposed model presents fine applicability and reliability for the predictions of plastic deformations,ductile damage,and fracture of anisotropic Mg alloys.

关键词： Ductile damage Anisotropy Phase field Constitutive relationship Magnesium

Plastic Effect on the Sliding Inception Bet ween a Cylinder and a Rigid Flat

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Acta Mechanica Solida Sinica 2019年第1期32卷 1-16页

作者： S.Zhang J.Huan H.Song x.liu Y.G.Wei LNM Institute of MechanicsChinese Academy of SciencesBeijing 100190China Department of Mechanical Engineering Johns Hopkins UniversityBaltimoreMD 21218USA College of Engineering Peking UniversityBeijing 100871China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China

The effec ts of mat erial plasticity and local slip on the sliding inception of asperity are studied in the present ***,a semi-analytical solution is derived under the full-stick condition to analyze the effect of material plasticity on sliding ***,a friction model with contact stiffness criterion is proposed to study the cases from partial-slip condition to full-stick *** element simulations with the provided model are used to present the friction *** friction coefficient of full-s tick interface converges at a st able value,approxima tely *** saturation appears as the normalized contact interference u*is larger than 3.A transition mechanism from slip-dominated to yield-dominated takes place in the sliding *** simulation results are compared with the semi-analytical solution.

关键词： Mat erial yielding Local slip Contact stiffness criterion Finite element simulation

Near-Earth Asteroids as the Parents of theδ-Cancrid Meteoroid Stream

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Research in Astronomy and Astrophysics 2024年第12期24卷 11-23页

作者： G.I.Kokhirova M.Zhang x.-G.Li A.I.Zhonmuhammadi x.liu Institute of Astrophysics National Academy of Sciences of TajikistanAyni 299/5Dushanbe734067Tajikistan xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China Key Laboratory for Radio Astronomy Chinese Academy of SciencesNanjing 210008China xinjiang Key Laboratory of Radio Astrophysics Urumqi 830011China University of Chinese Academy of Sciences Beijing 100049China

Theδ-Cancrid meteoroid stream forms four active meteor showers which are observable on the Earth annually during January–February and August–*** stream's definite parent comet has not been *** performed a search for near-Earth asteroids(NEAs)associated with this *** have followed the backward evolution of the orbital elements of a sample of NEAs and found their orbits at the Earth-crossing *** these orbits,we calculated the theoretical parameters of meteor showers associated with the considered *** carried out our search for observable active showers that match theoretically predicted ones with published data,and the result turned out that the predicted meteor showers of 13 NEAs were identified with the active showers produced by theδ-Cancrid meteoroid *** comet-like orbits of NEAs and established association with active meteor showers indicate their common cometary *** NEAs considered are moving within the stream and likely represent the dormant remnants of a parent comet of theδ-Cancrid asteroid-meteoroid complex that disintegrated more than 12 thousand years ago.

关键词： comets general-minor planets-asteroids-δ-Cancrids-meteorites-meteors-meteoroids

Dynamic Impact of High-Density Aluminum Foam

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Acta Mechanica Solida Sinica 2022年第2期35卷 198-214页

作者： Q.Peng J.xie H.S.Ma x.Ling x.liu Y.G.Wei LNM Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China School of Engineering and Technology China University of GeosciencesBeijing 100083China College of Engineering Peking UniversityBeijing 100871China

High-density aluminum foam can provide higher stiffness and absorb more energy during the impact Obtaining the constitutive law of such foam requires tri-axial tests with very high pressure,where difficulty may arise because the hydrostatic pressure can reach more than 30 *** this paper,instead of using tri-axial tests,we proposed three easier tests-tension,compression and shear to obtain the parameters of constitutive model(the Deshpande-Fleck model).To verify the constitutive model both statically and dynamically,we carried out addi-tional triaxial tests and direct impact tests,*** on the derived model,we performed finite element simulation to study the impact response of the present *** dimensional analysis,we proposed an empirical equation for a non-dimensional impact time the impact time divided by the time required for plastic wave travelling from the impact surface to the bottom surface,to det ermine the deformation charac teristic of the aluminum foam after *** the case with t_(d)≤1,the deformation tends to exhibit a shock-type characteristic,while for the case with t_(d)>5,the deformation tends to exhibit an upsetting-type characteristic.

关键词： High density aluminum Foam Deshpande-Fleck model Finite element method Impact analysis Plastic wave

Releasing the residual stress of C_(f)/SiC-GH3536 joint by designing an Ag-Cu-Ti+Sc_(2)(WO_(4))_(3) composite filler metal

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Journal of Materials Science & Technology 2022年第13期108卷 102-109页

作者： P.Wang x.liu H.Wang J.Cao J.Qi J.Feng State Key Laboratory of Advanced Welding and Joining Harbin Institute of TechnologyHarbin 150001China

Due to native character of thermal expansion coefficient(CTE)mismatch between C_(f)/SiC and GH3536,achieving high strength joint was a huge challenge for C_(f)/SiC-GH3536 ***,a composite filler metal of Ag-Cu-Ti+Sc_(2)(WO_(4))_(3) was developed to join C_(f)/SiC and *** work introduced Sc_(2)(WO_(4))_(3) to Ag-Cu-Ti system as a negative thermal expansion(NTE)reinforcing phase to release joint residual ***_(2)(WO_(4))_(3) was evenly distributed in the brazing seam and reacted with Ti to form Ti_(3)O_(5) reaction *** results of finite element analysis showed that the residual stress of the joints was effectively released by introducing Sc_(2)(WO_(4))_(3) reinforcing phase,and the mises stress was decreased from447 to 401 *** maximum shear strength of the C_(f)/SiC-GH3536 joint brazed with Ag-Cu-Ti+6 vol%Sc_(2)(WO_(4))_(3) filler alloys was 64 MPa,which was about 2.6 times higher than that of Ag-Cu-Ti *** results of this study provide a promising strategy for the introduction of new Sc_(2)(WO_(4))_(3) reinforcing phase in Ag-Cu-Ti system,and improve the reliability and feasibility of composite brazing alloy in brazing filed.

关键词： Negative thermal expansion Brazing Residual stress Composite brazing alloy CTE

Microstructure evolution and shape memory behaviors of Ni_(47)Ti_(44)Nb_(9)alloy subjected to multistep thermomechanical loading with different prestrain levels

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Journal of Materials Science & Technology 2024年第4期171卷 80-93页

作者： Y.H.Zhang H.Li Z.W.Yang x.liu Q.F.Gu State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an 710072China Shaanxi Key Laboratory of High-Performance Precision Forming Technology and Equipment Northwestern Polytechnical UniversityXi’an 710072China

Ni_(47)Ti_(44)Nb_(9)shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation *** application of shape memory effect depends on multistep thermomechan-ical loading,viz.,low-temperature deformation and subsequent heating to ***-temperature deformation prestrain plays a pivotal role in shape memory properties tailoring of SMA ***,microstructure evolution and deformation mechanisms of Ni_(47)Ti_(44)Nb_(9)SMA subjected to vari-ous prestrain levels are still *** this end,microstructure evolution and shape memory behaviors of Ni_(47)Ti_(44)Nb_(9)alloy subjected to multistep thermomechanical loading with prestrain levels of 8%-16%at-28℃(M_(s)+30℃)were *** results demonstrate that the stress-strain curve of the specimen exhibits four distinct stages at a maximal prestrain of 16%.Whereas stageⅡand stageⅢend at prestrains of∼8%and∼12%,*** stageⅡ,the stress-induced martensitic transformation is accompanied by the dislocation slip of the NiTi matrix andβ-Nb *** stageⅢ,in addition to the higher density of dislocations and further growth of stress-induced martensite variants(SIMVs),(001)compound twins are introduced as a result of the(001)deformation twinning in stress-induced ***{20-1}martensite twins are gradually introduced in stageⅣ.Correspondingly,after subsequent unloading and heating,a higher density of{114}austenite twins form in the specimen with a larger prestrain of 16%.With increasing prestrain from 8%to 16%,the recoverable strainε_(re)^(T)upon heating increases first and then ***ε_(re)^(T)obtains a maximum of 7.03%at 10%prestrain and de-creases to 6.17%at 16%*** increase ofε_(re)^(T)can be attributed to the formation of new SIMVs,the further growth of existing SIMVs,and the recoverable(001)compound *** the decrease ofε_(re)^(T)is mainly associated with the irrecoverable strain by{20−1}martensite *** effe

关键词： Ni_(47)Ti_(44)Nb_(9)shape memory alloy Wide transformation hysteresis Thermomechanical loading Microstructure evolution Shape memory behaviors Stress-induced martensitic transformation Deformation twinning

Numerical Study on Sinusoidal Fluctuated Pulsatile Laminar Flow Through Various Constrictions

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Communications in Computational Physics 2007年第1期2卷 99-122页

作者： T.S.Lee x.liu G.C.Li H.T.Low Department of Mechanical Engineering National University of SingaporeSingapore 119260.

Numerical simulations have been carried out for laminar sinusoidal pulsating flow in a tube with smooth single constriction.A second-order finite volume method has been developed to solve the fluid flow governing equations on a nonstaggered non-orthogonal *** effects of the Reynolds number,the Womersley number,the pulsatile amplitude,the constriction ratio and the constriction length on fluid flow in constricted tube will be *** will be demonstrated that the dynamic nature of the pulsating flow greatly depends on the frequency of the flow *** is observed that the peak wall vorticity seems to increase with the increase of Reynolds number,the pulsating amplitude and the constriction *** peak values of instantaneous wall vorticity are not greatly affected by the variation of Womersly *** constriction length does not put a significant impact on the flow instantaneous streamline behaviors compared with other ***,the peak wall vorticity increases monotonically with the decrease of the constriction length.

关键词： Numerical modeling constriction tube pulsatile flow control volume.