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cracking evolution behaviors of lightweight materials based on in situ synchrotron X-ray tomography： A review

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Frontiers of Mechanical Engineering 2018年第4期13卷 461-481页

作者： y. Luo S. c. Wu y. N. Hu y. N. Fu State Key Laboratory of Traction Power Southwest Jiaotong University Chengdu 610031 China Shanghai Synchrotron Radiation Facility Shanghai 201204 China

Damage accumulation and failure behaviors are crucial concerns during the design and service of a critical component, leading researchers and engineers to thoroughly identifying the crack evolution. Third-generation synchrotron radiation X-ray computed microtomo- graphy can be used to detect the inner damage evolution of a large-density material or component. This paper provides a brief review of studying the crack initiation and propagation inside lightweight materials with advanced synchrotron three-dimensional （3D） X-ray imaging, such as aluminum materials. Various damage modes under both static and dynamic loading are elucidated for pure aluminum, aluminum alloy matrix, aluminum alloy metal matrix composite, and aluminum alloy welded joint. For aluminum alloy matrix, metallurgical defects （porosity, void, inclusion, precipitate, etc.） or artificial defects （notch, scratch, pit, etc.） strongly affect the crack initiation and propagation. For aluminum alloy metal matrix composites, the fracture occurs either from the particle debonding or voids at the particle/matrix interface, and the void evolution is closely related with fatigued cycles. For the hybrid laser welded aluminum alloy, fatigue cracks usually initiate from gas pores located at the surface or sub-surface and gradually propagate to a quarter ellipse or a typical semi-ellipse profile.

关键词： fatigue crack initiation and growth fatigue damage mechanism damage tolerance defect characterization laser welded aluminum alloys

Non-contact evaluation of the resonant frequency of a microstructure using ultrasonic wave

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Acta Mechanica Sinica 2010年第2期26卷 317-323页

作者： X. Kang X. y. He c.J. Tay c. Quan Department of Applied Mechanics Nanjing University of Science and Technology 210094 Nanjing China Institute of Engineering Mechanics Southeast University210096 Nanjing China Department of Mechanical Engineering National Universityof Singapore 9 Engineering Drive 1 117576 Singapore Singapore

This paper presents a novel non-contact method for evaluating the resonant frequency of a microstructure, Firstly, the microstructure under test is excited by ultrasonic waves. This excitation method does not impose any undefined load on the specimen like the electrostatic excitation and also this is the first actual use of ultrasonic wave for exciting a microstructure in the literature. Secondly, the amplitudes of the microstructure are determined by image edge detection using a Mexican hat wavelet transform on the vibrating images of the microstructure. The vibrating images are captured by a ccD camera when the microstructure is vibrated by ultrasonic waves at a series of discrete high frequencies （〉30 kHz）. Upon processing the vibrating images, the amplitudes at various excitation frequencies are obtained and an amplitude-frequency spectrum is obtained from which the resonant frequency is subsequently evaluated. A micro silicon structure consisting of a perforated plate （192 × 192 μm） and two cantilever beams （76 × 43 μm） which is about 4 μm thickness is tested. Since laser interferometry is not required, thermal effects on a test object can be avoided. Hence, the setup is relatively simple. Results show that the proposed method is a simple and effective approach for evaluating the dynamic characteristics of microstructures.

关键词： Non-contact Microstructure· Resonant frequency Ultrasonic wave Image processing

Unusual F_(3)stacking fault in magnesium

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Journal of Magnesium and Alloys 2023年第7期11卷 2404-2428页

作者： y.yue S.L.yang c.c.Wu J.F.Nie Department of Materials Science and Engineering Monash UniversityVictoria 3800Australia

An unusual F_(3)basal stacking fault resulting from twin-dislocation interaction in magnesium is observed in molecular dynamics *** F_(3)fault is produced in the twin lattice from the interaction between a migrating(1012)twin boundary and a partial dislocation of either a prismaticc>edge,or a prismaticc+a>mixed dislocation in the *** condition is that the partial dislocation needs to have a negative sign and lie on a plane intersecting a compression site of the twin *** F_(3)fault can also be generated when a positive basalmixed dislocation in the twin lattice,with slip plane intersecting a compression site of the twin boundary,interacts with a basal-prismatic twinning *** F_(3)fault comprises two I_(1) faults that have the same character but are separated by two basal *** has one end connected to the twin boundary,and the other end bounded by a lattice defect with a Burgers vector identical to that of a 30°Shockley partial *** formation frequency of the F_(3)fault is higher at a lower shear stress(below∼400 MPa)and/or a lower temperature(100 K and 200 K).The F_(3)fault can decompose into a glissile 30°Shockley and a T_(2) fault at a temperature above∼400 *** relationships between the F_(3)fault and other types of basal stacking faults such as I_(2),T_(2) or paired I_(1) faults that are separated by multiple basal layers are discussed.

关键词： Magnesium Basal stacking fault F3 fault Twin-dislocation interactions

Natural vibration of cantilever porous twisted plate with variable thickness in different directions

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Defence Technology（防务技术） 2023年第9期27卷 200-216页

作者： y.X.Hao y.y.Liu W.Zhang L.T.Liu K.c.Sun S.W.yang college of Mechanical Engineering Beijing Information Science and Technology UniversityBeijing100192PR China college of Mechanical Engineering Beijing University of TechnologyBeijing100124PR China

In this paper,the blade is assumed to be a rotating variable thickness cantilever twisted plate structure,and the natural vibrations of variable thickness cantilever twisted plate made of metal porous material are *** is assumed that the thickness of the plate changes along spanwise direction and chordwise direction,respectively,and it changes in both *** classical thin shell theory,the first and second fundamental forms of surface and von Karman geometric relationship are employed to derive the total potential energy and kinetic energy of the cantilever twisted plate,in which the centrifugal force potential due to high rotational speed is ***,according to the Rayleigh-Ritz procedure and applying the polynomial functions which satisfy the cantilever boundary conditions,the dynamic system expressed by equations of motion is reduced to an eigenvalue *** numerical simulation,the frequency curves and the mode shapes of the twisted plate can be obtained to reveal the internal connection between natural vibration and the parameters.A series of comparison studies are performed to verify the accuracy of the present formulation and calculations,in which compared data come from experimental,finite element method and theoretical calculation,*** influence of pre-twist angle,three different forms of thickness taper ratio and rotational speed on natural vibration,mode exchange and frequency veering phenomenon of the system is discussed in *** addition,the approach proposed here can efficiently extract analytical expressions of mode functions for rotating variable thickness cantilever twisted plate structures.

关键词： Porous cantilever twisted plate Variable thickness Natural vibration Frequency veering Mode exchange

Statistical moment-based structural damage detection method in time domain

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Earthquake Engineering and Engineering Vibration 2013年第1期12卷 13-23页

作者： J.Zhang y.L.Xu J.Li y.Xia J.c.Li Department of civil and Environmental Engineering The Hong Kong Polytechnic University Department of Building Engineering Tongji University Faculty of Engineering University of Technology Sydney

A novel structural damage detection method with a new damage index,i.e.,the statistical moment-based damage detection（SMBDD） method in the frequency domain,has been recently *** aim of this study is to extend the SMBDD method in the frequency domain to the time domain for building structures subjected to non-Gaussian and non-stationary *** applicability and effectiveness of the SMBDD method in the time domainis verified both numerically and *** buildings with various damage scenarios are first numerically investigated in the time domain taking into account the effect of measurement *** applicability of the proposed method in the time domain to building structures subjected to non-Gaussian and non-stationary excitations is then experimentally investigated through a series of shaking table tests,in which two three-story shear building models with four damage scenarios *** identified damage locations and severities are then compared with the preset *** comparative results are found to be satisfactory,and the SMBDD method is shown to be feasible and effective for building structures subjected to non-Gaussian and non-stationary excitations.

关键词： damage detection statistical moment time domain non-Gaussian non-stationary experimental investigation

Plasma enhanced diamond deposition on steel and Si substrates

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Acta Metallurgica Sinica(English Letters) 2009年第5期22卷 321-329页

作者： y.S. Li y. Tang Wo chen Q. yang c.Xiao A. Hirose Plasma Physics Laboratory University of Saskatchewan Saskatoon SK S7N 5E2 Canada Department of Mechanical Engineering University of Saskatchewan Saskatoon S7N 5A9 Canada

Diamond growth on Fe-cr-Al-Si steel and Si substrates was comparatively investigated in microwave plasma enhanced chemical vapor deposition （MPcVD） reactor with different deposition parameters. Adherent nanocrystalline diamond films were directly deposited on this steel substrate under a typical deposition condition, whereas microcrystalline diamond films were produced on Si wafer. With increasing cH4 concentration, reaction pressure, or the total gas flow rate, the quality of nanocrystalline diamond films formed on Fe-cr-Al-Si substrates is gradually deteriorated in terms of density and adhesion. This impaired diamond quality on steels is primarily associated with a combined effect by the substrate composition and the specific process conditions that favor excessive nucleation of diamond.

关键词： Plasma cVD Diamond film Steel Si

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chinese Annals of Mathematics,Series B 2002年第2期23卷 149-164页

作者： c.BARDOS y.GUO W.STRAUSS Universite DivisionDepartment Denis Diderot and LAN Universite Pierre et Marie CurieParisFrance.of Applied MathematicsBrown UniversityProvidenceRhode Island 02912U?

The authors investigate the stability of a steady ideal plane flow in an arbitrary domain in terms of the L^2 norm of the vorticity. Linear stability implies nonlinear instability provided the growth rate of the linearized system exceeds the Liapunov exponent of the flow. In contrast,a maximizer of the entropy subject to constant energy and mass is stable. This implies the stability of certain solutions of the mean field equation.

关键词： Stable ideal plane flows Unstable ideal plane flows Liapunov exponent

PREPARATION OF MULTI-WALLED cARBON NANOTUBES USING NiO cATALyST SyNTHESIZED By HyDROTHERMAL METHOD

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Acta Metallurgica Sinica(English Letters) 2003年第5期16卷 416-420页

作者： y.J.Zhu y.L.chen X.M.Xue y.M.chen c.y.Wu T.c.Kuang S.H.Li H.y.Zhang DepartmentofAppliedPhysics GuangdongUniversityofTechnologyGuangzhou510090China centerofAnalysisTesting GuangdongUniversityofTechnologyGuangzhou510O9OChina FacultyofMaterialandEnergy GuangdongUniversityofTechnologyGuangzhou510090.China

The Ni(OH)2/SiO2 binary colloid was prepared using Ni(NO3)2.6H2O and (c2H5O)4SiO4 as starting materials and was used to form NiO/SiO2. composite powder by hydrothermal method and desiccant method in open air respectively. Multi-walled carbon nanotubes (MWcNTs) were synthesized respectively by chemical vapor deposition using the NiO/SiO2 catalyst prepared by different methods. The phase and morphology of the catalysts and the morphology, output yield and purity of MWcNTs were compared by XRD, TEM and SEM. The results show that the catalyst powder prepared by hydrothermal method, compared with that by desiccant method, is smaller, better dispersion and has stronger catalytic activity. Pure MWcNTs with smaller tube diameter and narrow range could be obtained at a high yield using that NiO/SiO2 powder prepared by hydrothermal method as catalyst.

关键词： hydrothermal method dry method at atmosphere carbon nan- otube catalytic pyrolysis

Relationship Between coarse/Fine Aggregate Space coefficient and Properties of Self-compacting concrete

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武汉理工大学学报 2010年第17期32卷 158-164,169页

作者： LONG G c LIU y H XIE y J School of civil Engineering and Architecture Central South UniversityChangsha 410075China Quality Intendance and Inspect Station of construction Engineering Chenzhou 423000China

For the sake of expounding the relationship between coarse/fine aggregate volume content and properties of self-compacting concrete(Scc),a parameter of aggregate space coefficient is proposed to study systematically the effects of fine/ coarse aggregates on workability,strength and volume stability of Scc by experiments. The optimized coarse/fine aggregates volume content of Scc was discussed with regard to specified properties. Results indicate there is a close relationship between aggregate space coefficient and properties of Scc not only in fresh state but also in hardened state. With the increasing coarse/fine aggregate space coefficients,workability of fresh Scc will be improved,the compressive strength decreases slightly and shrinkage of Scc however increases. When coarse aggregate space coefficient ranges from 1.2 to 1.7 and the fine aggregate space coefficients is from 0.6 to 1.0,Scc can meet self-compactability requirements in fresh state and have a good volume stability and appropriate strength in hardened state. The results will benefits for developing a new mixing design method for Scc.

关键词： self-compacting concrete aggregate space coefficient workability compressive strength shrinkage