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ON THE MECHANISM OF THE FORMATION OF HORIZONTAL CRACKS IN A VERTICAL COLUMN OF SATURATED SAND

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Acta Mechanica Sinica 2001年第1期17卷 1-9页

作者：郑哲敏谈庆明彭福骄 State key laboratory of nonlinear mechanics Institute of Mechanics Chinese Academy of Sciences Beijing China 100080 Institute of mechanics Chinese Academy of Sciences Beijing China 100080

Extended horizontal cracks have! been observed experimentally in a vertical column of saturated sand when a flow of water is forced to percolate upward through it. This paper provides a theory for this phenomenon. It will be shown that the presence of inhomogeneity in permeability along the length of the column is essential for such cracks to develop. It will also be shown that small initial inhomogeneity may be magnified through the transport of the finer component of the sand by percolation. Under certain conditions liquefaction takes place at a section of the sand column causing a crack to initiate and grow there. This theory is found to be in good qualitative agreement with the experimental findings.

关键词： liquefaction cracks percolation

Effect of Structural Relaxation on Deformation Behaviour of Zr-Based Metallic Glass

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Chinese Physics Letters 2006年第7期23卷 1868-1871页

作者：刘渊张泰华魏炳忱邢冬梅李维火张凌晨 National Microgravity laboratory Institute of Mechanics Chinese Academy of Sciences Beijing 100080 State key laboratory of nonlinear mechanics (LNM) Institute of Mechanics Chinese Academy of Sciences Beijing 100080

Structural relaxation through isothermal annealing at temperature below glass transition is conducted on Zr46.75 Ti8.25 CU7.5Ni11Be27.5 （Vitreloy-4） bulk metallic glass. Defect concentration is correlated with the annealing time t according to differential scanning calorimetry thermalgrams. The effects of structural relaxation on mechanical properties and deformation behaviour are investigated by using instrumented nanoindentation. It is found that the as-cast alloy exhibits pronounced serration flow during the loading process of nanoindentation, and the size and number of the serrations decrease with the annealing time. The change of the deformation behaviour with structural relaxation is explained using a free volume model.

关键词： NANOINDENTATION ALLOYS FLOW EMBRITTLEMENT TEMPERATURE

Single-legweight limit of fixation model of simple supracondylar fracture of the femur

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Acta Mechanica Sinica 2019年第4期35卷 926-939页

作者： Guo-Yu Bai Xiang-Hong Xu Jin-Hui Wang Ning Sun Tianjin key laboratory of Modern Engineering mechanics Department of Mechanics Tianjin UniversityTianjin 300072 China State key laboratory of nonlinear mechanics Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China Beijing Jishuitan Hospital Beijing 100035China

Postoperative early rehabilitation training for supracondylar fracture of femur aids in accelerating the healing of fractures with shorter recovery periods. Presently, clinical studies on post-operative early weight training are still in the nascent stages. The weight bearing capacity at different healing stages typically depends on clinical experience and there is a lack of standards to quantify the weight that would be conducive to the healing of fractures. In this paper, a 3D geometric model of the femur is obtained using imaging data, a locking plate fixation model of a simple supracondylar fracture of the femur, which considers the angle and spatial direction of the fracture surface, is established, the stress distribution and load transmission mechanism of the fracture fixation model on a single leg standing posture are studied and the weight bearing capacity of a standing single leg at the early stage of fracture is given. This provides the basis for objective quantification of postoperative early weight bearing capacity.

关键词： Simple supracondylar fracture of the femur Early weight bearing Single-leg weight limit

Biomechanical research into lamina cribrosa in glaucoma

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National Science Review 2020年第8期7卷 1277-1279页

作者： Long Li Fan Song State key laboratory of nonlinear mechanics and Beijing key laboratory of Engineered Construction and Mechanobiology Institute of MechanicsChinese Academy of Sciences School of Engineering Science University of Chinese Academy of Sciences

Glaucoma, a leading cause of irreversible blindness, poses a considerable public health challenge and burden. Mechanical models of the lamina cribrosa under elevated intraocular pressure at different scales, contributing significantly to uncovering the glaucomatous pathogenesis, are discussed. Meanwhile, the open issues and avenues for further development are highlighted.

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Second mode unstable disturbance measurement of hypersonic boundary layer on cone by wavelet transform

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Acta Mechanica Sinica 2011年第4期27卷 488-493页

作者： Jian Han.Nan Jiang.Yan Tian Department of Mathematics,Tianjin University,300072 Tianjin,China Department of mechanics,Tianjin University,300072 Tianjin,China Tianjin key laboratory of Modern Engineering mechanics,300072 Tianjin,China State key laboratory of nonlinear mechanics,Institute of mechanics,Chinese Academy of Sciences,100190 Beijing,China Department of Mathematics Tianjin University Tianjin China Department of mechanics Tianjin University Tianjin China Tianjin key laboratory of Modern Engineering mechanics Tianjin China State key laboratory of nonlinear mechanics Institute of Mechanics Chinese Academy of Sciences Beijing China

Experimental investigation of hypersonic boundary layer instability on a cone is performed at Mach number 6 in a hypersonic wind tunnel. Time series signals of instantaneous fluctuating surface-thermal-flux are measured by Pt-thin-film thermocouple temperature sensors mounted at 28 stations on the cone surface in the streamwise direction to investigate the development of the unstable disturbance. Wavelet transform is employed as a mathematical tool to obtain the multi-scale characteristics of fluctuating surfacethermal-flux both in the temporal and spectrum space. The conditional sampling algorithm using wavelet coefficient as an index is put forward to extract the unstable disturbance waveform from the fluctuating surface-thermal-flux *** generic waveform for the second mode unstable disturbance is obtained by a phase-averaging technique. The development of the unstable disturbance in the streamwise direction is assessed both in the temporal and spectrum space. Our study shows that the local unstable disturbance detection method based on wavelet transformation offers an alternative powerful tool in studying the hypersonic unstable mode of laminar-turbulent transition. It is demonstrated that, at hypersonic speeds, the dominant flow instability is the second mode, which governs the course of laminar-turbulent transition of sharp cone boundary layer.

关键词： Hypersonic boundary layer. Sharp cone Insta-bility Wavelet transform

Effects of laser power density on static and dynamic mechanical properties of dissimilar stainless steel welded joints

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Acta Mechanica Sinica 2012年第5期28卷 1334-1339页

作者： Yan-Peng Wei Mao-Hui Li Gang Yu Xian-Qian Wu Chen-Guang Huang Zhu-Ping Duan key laboratory of Hydrodynamics and Ocean Engineering Institute of MechanicsChinese Academy of Sciences The Quartermaster Equipment Research Institute of the General Logistics Department of PLA key Lab of mechanics in Advanced Manufacturing Institute of MechanicsChinese Academy of Sciences The State key laboratory of nonlinear mechanics Institute of MechanicsChinese Academy of Sciences

The mechanical properties of laser welded joints under impact loadings such as explosion and car crash etc. are critical for the engineering designs. The hardness, static and dynamic mechanical properties of AISI304 and AISI316L dissimilar stainless steel welded joints by CO2 laser were experimentally studied. The dynamic strainstress curves at the strain rate around 103 s-1 were obtained by the split Hopkinson tensile bar （SHTB）. The static mechanical properties of the welded joints have little changes with the laser power density and all fracture occurs at 316 L side. However, the strain rate sensitivity has a strong depen- dence on laser power density. The value of strain rate factor decreases with the increase of laser power density. The welded joint which may be applied for the impact loading can be obtained by reducing the laser power density in the case of welding quality assurance.

关键词： Laser welding Dynamic mechanics Strain rate.Power density

Effects of loading condition on very-high-cycle fatigue behaviour and dominant variable analysis

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Science China(Physics,mechanics & Astronomy) 2014年第1期57卷 74-82页

作者： LEI ZhengQiang XIE JiJia SUN ChengQi HONG YouShi State key laboratory of nonlinear mechanics Institute of Mechanics Chinese Academy of Sciences PetroChina Pipeline R&D Center

The specimens of a high carbon chromium steel were quenched and tempered at 150℃, 180℃ and 300℃. Such specimens were tested via rotating bending and a push-pull type of axial loading to investigate the influences of loading condition on the behaviour of very-high-cycle fatigue （VHCF）. Experimental results show the different influences of inclusion size on the fa- tigue life for the two loading conditions. Predominant factors and mechanism for the fine-granular-area （FGA） of crack origin were discussed. In addition, a reliability analysis based on a modified Tanaka-Mura model was carried out to evaluate the sen- sitivity of inclusion size, stress, and AKFGA to the life of VHCF crack initiation.

关键词： very-high-cycle fatigue FGA loading condition life scatter inclusion

Dynamic equations for curved submerged floating tunnel

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Applied Mathematics and mechanics(English Edition) 2007年第10期28卷 1299-1308页

作者：董满生葛斐张双寅洪友士 State key laboratory of nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100080P.R.China

In virtue of reference Cartesian coordinates, geometrical relations of spatial curved structure are presented in orthogonal curvilinear coordinates. Dynamic equations for helical girder are derived by Hamilton principle. These equations indicate that four generalized displacements are coupled with each other. When spatial structure degenerates into planar curvilinear structure, two generalized displacements in two perpendicular planes are coupled with each other. Dynamic equations for arbitrary curvilinear structure may be obtained by the method used in this paper.

关键词： submerged floating tunnel (SFT) dynamic equations Hamilton principle,curved girder

NANO-TRIBOLOGICAL STUDY ON A SUPER-HYDROPHOBIC FILM FORMED ON ROUGH ALUMINUM SUBSTRATES

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Acta Mechanica Sinica 2004年第2期20卷 159-164页

作者：任嗣利杨生荣赵亚溥 State key laboratory of Solid Lubrication Lanzhou Institute of Chemical PhysicsChinese Academy of SciencesLanzhou 730000China State key Laboratory of Nonlinear MechanicsInstitute of MechanicsChinese Academy of SciencesBeijing 100080China State key laboratory of Solid Lubrication Lanzhou Institute of Chemical PhysicsChinese Academy of SciencesLanzhou 730000China State key laboratory of nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100080China

A novel super-hydrophobic stearic acid(STA)film with a water contact angle of 166° was prepared by chemical adsorption on aluminum wafer coated with polyethyleneimine(PEI)film. The micro-tribological behavior of the super-hydrophobic STA monolayer was compared with that of the polished and PEI-coated Al *** effect of relative humidity on the adhesion and friction was investigated as *** was found that the STA monolayer showed decreased friction,while the adhesive force was greatly decreased by increasing the surface roughness of the Al wafer to reduce the contact area between the atomic force microscope(AFM)tip and the sample surface to be *** the friction and adhesion of the Al wafer was effectively decreased by generating the STA monolayer, which indicated that it could be feasible and rational to prepare a surface with good adhesion resistance and lubricity by properly controlling the surface morphology and the chemical *** the adhesion and friction decreased as the relative humidity was lowered from 65% to 10%,though the decrease extent became insignificant for the STA monolayer.

关键词： nano-tribology adhesion friction super-hydrophobic AFM/FFM