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Progress in Natural Science:Materials International 2005年第8期15卷 742-748页

作者： LIANG Weiguo 1,2. and ZHAO Yangsheng1(1. Mining technology Institute, taiyuan university of technology, {2., china 2. Rock and Soil mechanics Institute, Chinese Academy of Sciences, Wuhan 430071, china) Mining technology Institute Taiyuan University of Technology Taiyuan 030024 China Rock and Soil mechanics Institute Chinese Academy of Sciences Wuhan 430071 China

The hydraulic fracture in rock salt is a complicated solid fluid and mass transfer coupling process. Through theoretical analysis, a solid fluid and mass transfer coupling mathematical model of hydraulic fracture in rock salt is established in this work, and numerical simulations are carried out with the model. The simulation results indicate that rock salt cracks in the typical way of wing-crack(or tensile crack) during the fracture, and the relation of fracture aperture (w) with expanding distance (x) and fracture time (t) is w=(0.0034+0.0006t)e (0.0007+0.0018t)x. Furthermore, it has been found that both the water pressure in the crack and the expanding velocity of the crack decrease gradually as a result of the influence of salt dissolving during fracturing. These numerical simulations well illustrate the process of hydraulic fracture in rock salt and are significantly meaningful in engineering practice.

关键词： rock salt hydraulic fracture solid liquid and mass transfer coupling mathematical model numerical simulation.

A study on compressive shock wave propagation in metallic foams

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Science china(Physics,mechanics & Astronomy) 2010年第2期53卷 279-287页

作者： WANG ZhiHua1,2.ZHANG YiFen2.REN HuiLan1 & ZHAO LongMao2.1 State Key Laboratory of Explosion Science and technology,Beijing Institute of technology,Beijing 100081,{2. 2.Institute of applied mechanics and biomedical engineering,taiyuan university of technology,taiyuan 03002.,{2. State Key Laboratory of Explosion Science and technology Beijing Institute of Technology Beijing China Institute of applied mechanics and {2. engineering Taiyuan University of Technology Taiyuan China

Metallic foam can dissipate a large amount of energy due to its relatively long stress plateau,which makes it widely applicable in the design of structural crashworthiness. However,in some experimental studies,stress enhancement has been observed when the specimens are subjected to intense impact loads,leading to severe damage to the objects being protected. This paper studies this phenomenon on a 2. mass-spring-bar model. With the model,a constitutive relationship of metal foam and corresponding loading and unloading criteria are presented; a nonlinear kinematics equilibrium equation is derived,where an explicit integra-tion algorithm is used to calculate the characteristic of the compressive shock wave propagation within the metallic foam; the effect of heterogeneous distribution of foam microstructures on the shock wave features is also included. The results reveal that under low impact pulses,considerable energy is dissipated during the progressive collapse of foam cells,which then reduces the crush of objects. When the pulse is sufficiently high,on the other hand,stress enhancement may take place,especially in the heterogeneous foams,where high peak stresses usually occur. The characteristics of compressive shock wave propagation in the foam and the magnitude and location of the peak stress produced are strongly dependent on the mechanical properties of the foam material,amplitude and period of the pulse,as well as the homogeneity of the microstructures. This research provides valuable insight into the reliability of the metallic foams used as a protective structure.

关键词： aluminum foam heterogeneous intensive pulse loading stress enhancement

A complex variable meshless method for fracture problems

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Science china(Physics,mechanics & Astronomy) 2006年第1期49卷 46-59页

作者： CHENG Yumin1 & LI Jiuhong2.1. Shanghai Institute of applied Mathematics and mechanics, Shanghai {2., Shanghai 2.0072. china 2. Department of Building engineering, Xi’an {2. of technology, Xi’an 710048, china Shanghai Institute of applied Mathematics and mechanics Shanghai University Shanghai China Department of Building engineering Xi’an University of Technology Xi’an China

Based on the moving least-square (MLS) approximation, the complex variable moving least-square approximation (CVMLS) is discussed in this paper. The complex variable moving least-square approximation cannot form ill-conditioned equations, and has greater precision and computational efficiency. Using the analytical solution near the tip of a crack, the trial functions in the complex variable moving least-square approxi- mation are extended, and the corresponding approximation function is obtained. And from the minimum potential energy principle, a complex variable meshless method for fracture problems is presented, and the formulae of the complex variable meshless method are obtained. The complex variable meshless method in this paper has greater precision and computational efficiency than the conventional meshless method. Some examples are given.

关键词： moving least-square approximation, complex variable moving least-square approximation, meshless method, complex variable meshless method, fracture.

Numerical and experimental investigation of the fracture behavior of shock loaded alumina

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Science china(Physics,mechanics & Astronomy) 2010年第2期53卷 244-252页

作者： REN HuiLan1,SHU XueFeng2.& LI Ping3 1 State Key Laboratory of Explosion Science and technology,Beijing Institute of technology,Beijing 100081,{2. 2.Institute of applied mechanics and biomedical engineering,taiyuan university of technology,taiyuan 03002.,{2. 3 Labroratory for Shock Wave and Detonation Physics Research,Institute of Fluid Physics,CAEP,Mianyang 610059,{2. State Key Laboratory of Explosion Science and technology Beijing Institute of Technology Beijing China Institute of applied mechanics and {2. engineering Taiyuan University of Technology Taiyuan China Labroratory for Shock Wave and Detonation Physics Research Institute of Fluid Physics CAEP Mianyang China

Plate impact expeiments are conducted to investigate the dynamic behavior of alumina by using one stage light gas gun. A ve-locity interferometer system for reflectors (VISAR) is used to obtain Hugoniot elastic limit and the free surface velocity profile,which consists of an elastic wave followed immediately by a dispersive inelastic wave. The stress histories under different impact velocities are measured by in-material manganin gauges. Based on the experimental data a Hugoniot curve is fitted,which shows the compressive characteristics that alumina changes typically from elastic to "plastic" ,and under higher pressure it will be transferred to similar-fluid state. The turning point of the Hugoniot curve from a high pressure region to a low pressure region is about 11.4 GPa. The fracture process of alumina is simulated by way of finite element code. After the analysis of the fracture mechanism,the numerical results show an important role played by the nucleation and the growth of the cracks in the macro-scopic fracture of the alumina target. The numerical predictions of stress histories are compared with the experimental results,which indicates consistency between them.

关键词： plate impact experiment hugoniot curve fracture characteristics numerical simulation

Fracture analysis of a functionally graded interfacial zone between two dissimilar homogeneous materials

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Science china(Physics,mechanics & Astronomy) 2006年第5期49卷 540-552页

作者： CHENG Zhanqi1,2.& ZHONG Zheng1 1. School of Aerospace engineering and applied {2., Tongji university, Shanghai 2.0092. china 2. College of Civil engineering, Zhengzhou university, Zhengzhou 450002. china School of Aerospace engineering and applied {2. Tongji University Shanghai China College of Civil engineering Zhengzhou University Zhengzhou China

In this paper the plane elasticity problem for a functionally graded interfacial zone containing a crack between two dissimilar homogeneous materials has been considered. It is assumed that in the interfacial zone the reciprocal of the shear modulus is a linear function of the coordinate, while Possion’s ratio keeps constant. By utilizing the Fourier transformation technique and the transfer matrix method, the mixed boundary problem is reduced to a system of singular integral equations that are solved numerically. The influences of the geometric parameters and the graded parameter on the stress intensity factors are investigated. The numerical results show that the graded parameters, the thickness of interfacial zone, the crack size and location have significant effects on the stress intensity factors.

关键词： functionally graded material interfacial zone fracture stress intensity factor

The dust emission law in the wind erosion process on soil surface

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Science china(Physics,mechanics & Astronomy) 2009年第2期52卷 258-269页

作者： XING Mao1 & GUO LieJin2.1 Mining technology Institute, taiyuan university of technology, {2., china 2.State Key Laboratory of Multiphase Flow in Power engineering, Xi’an Jiaotong university, Xi’an 710049, china Mining technology Institute Taiyuan University of Technology Taiyuan China State Key Laboratory of Multiphase Flow in Power engineering Xi’an Jiaotong University Xi’an China

The dust emission models to date cannot describe the relation between the transport rate of different sized grains and their grain size composition in soil surface, so Aeolian grain transport on a soil-like bed composed of fine sand and silt powder was measured in a wind tunnel. Six types of soil-like beds with different silt fractions have been tested in this experiment. The mass flux profiles of silt dust and sand grains are much different due to their different motion modes. Analysis of the vertical distribution of the powder and sand grains reveals that for a given soil bed, the ratio of the horizontal dust flux to the horizontal sand flux is directly proportional to their mass ratio in the bed. The dust flux is closely linked to the sand flux by the bombardment mechanism. For a given wind velocity and grain size of the bed, the slopes of the vertical mass flux profiles of sand grains larger than 100 μm are nearly equal in a log-linear plot and the ratio between the fraction of transport rate of each size group to the whole transport rate and the mass fraction of each size group in the bed is a constant only dependent on grain size. With this law, the transport rate of dust and different sized grains can be related with the grain size composition in the soil surface.

关键词： wind erosion dust transport rate grain size

Boundary element-free method for elastodynamics

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Science china(Physics,mechanics & Astronomy) 2005年第6期48卷 641-657页

作者： CHENG Yumin1 & PENG Miaojuan2.1. Shanghai Institute of applied Mathematics and mechanics, Shanghai {2., Shanghai 2.0072. china 2. Department of Civil engineering, Shanghai {2., Shanghai 2.0072. china Shanghai Institute of applied Mathematics and mechanics Shanghai University Shanghai China Department of Civil engineering Shanghai University Shanghai China

The moving least-square approximation is discussed first. Sometimes the method can form an ill-conditioned equation system, and thus the solution cannot be obtained correctly. A Hilbert space is presented on which an orthogonal function system mixed a weight function is defined. Next the improved moving least-square approximation is discussed in detail. The improved method has higher computational efficiency and precision than the old method, and cannot form an ill-conditioned equation system. A boundary element-free method (BEFM) for elastodynamics problems is presented by combining the boundary integral equation method for elastodynamics and the improved moving least-square approximation. The boundary element-free method is a meshless method of boundary integral equation and is a direct numerical method compared with others, in which the basic unknowns are the real solutions of the nodal variables and the boundary conditions can be applied easily. The boundary element-free method has a higher computational efficiency and precision. In addition, the numerical procedure of the boundary element-free method for elastodynamics problems is presented in this paper. Finally, some numerical examples are given.

关键词： moving least-square approximation, improved moving least-square approximation, elastodynamics, boundary integral equation, meshless method, boundary element-free method, Fourier eigen transform.

Electric-stimulus rate encoding algorithm of Mandarin tonal information in cochlear implant

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Progress in Natural Science:Materials International 2006年第12期16卷 1315-1321页

作者： GUAN Tian~1, GONG Qin~1 and YE Datian~2.*(1. Department of biomedical engineering, Tsinghua {2., Beijing 100084, china 2. Research Center of biomedical engineering, Graduate School at Shenzhen, Tsinghua {2., Shenzhen 518055, china) Department of biomedical engineering Tsinghua University Beijing 100084 China Research Center of biomedical engineering Graduate School Shenzhen Tsinghua University Shenzhen 518055 China

The modern multi-channel cochlear implants usually extract and encode the temporal envelope cues. This kind of algorithms can hardly satisfy the users who speak tonal languages, such as Mandarin. Many studies have tried to enhance the recognition ability of Mandarin through encoding tonal information and made suggestions to frequency-modulate the fixed pulse-rate carrier with the extracted tonal information based on the rate-pitch theory in electric hearing. However, how to encode and deliver the tonal information such as F_0by changing electric-stimulus rate has not got further study in clinical electric-stimulus mode. The present paper focuses on this matter by piecewise calculating the appreciable electric-stimulus rates. Then an electric-stimulus encoding algorithm of Mandarin tone is brought forward and testified through acoustic simulations. Such conclusion can be drawn that this algorithm of electric-stimulus rate could convey tonal information well and help to enhance the Mandarin speech recognition ability.

关键词： cochlear implant tone fundamental frequency electric-stimulus rate.

A low frequency piezoelectric power harvester using a spiral-shaped bimorph

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Science china(Physics,mechanics & Astronomy) 2006年第6期49卷 649-659页

作者： HU Yuantai1,2.HU Hongping2.& YANG Jiashi3 1. Institute of mechanics and Sensing technology,Central South {2.,Changsha 410083,china 2. Department of mechanics,Huazhong {2. of Science and technology,Wuhan 430074,china 3. Department of engineering mechanics,{2. of Nebraska,Lincoln,NE 68588-052.,USA Institute of mechanics and Sensing technology Central South University Changsha China Department of mechanics Huazhong University of Science and Technology Wuhan China Department of engineering mechanics University of Nebraska Lincoln USA

We propose a spiral-shaped piezoelectric bimorph power harvester operating with coupled flexural and extensional vibration modes for applications to low frequency energy sources. A theoretical analysis is performed and the computational results show that the spiral structure has relatively low operating frequency compared to beam power harvesters of the same size. It is found that to optimize the performance of a piezoelectric spiral-shaped harvester careful design is needed.

关键词： spiral-shaped bimorph,piezoelectric harvester,power density.

The numerical method for three-dimensional impact with friction of multi-rigid-body system

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Science china(Physics,mechanics & Astronomy) 2006年第1期49卷 102-118页

作者： ZHAO Zhen1,2. LIU Caishan2.& CHEN Bin2.1. Beijing Institute of Graphic Communication, Beijing 102.00, china 2. Department of mechanics & {2. Science, Peking university, Beijing 100871, china Beijing Institute of Graphic Communication Beijing China Department of mechanics & engineering Science Peking University Beijing China

The differential equations for planar impacts reduce to an algebraic form, and can be easily solved. For three dimensional impacts with friction, there is no closed-form solution, and numerical integration is required due to the swerve behavior of tangential impulse during collisions. The dynamic governing equations in the impact process are built up in impulse space based on the Lagrangian equation in this paper. The coefficient of restitution defined by Poisson is used as the condition of impact termination. A valid nu- merical method for solving three-dimensional frictional impact of multi-rigid body system is established. The singular cases of tangential movement in sticking point are especially noticed and analyzed. Several examples are present to reveal the different kinds of tan- gential movement modes varied with the normal impulse during collision.

关键词： multi-rigid body, impact, friction.