力学学报

ANTI-BLAST ANALYSIS OF CELLULAR SACRIFICIAL CLADDING

Ding Yuanyuan, Wang Shilong, Zheng Zhijun, Yang Liming, Yu Jilin

The behavior of a cellular sacrificial cladding for blast attenuation was studied by using 1D shock models and 3D cell-based finite element models. Based on a rate-independent, rigid-plastic hardening (R-PH) idealization, a shock model was developed and an equation governing the shock wave propagation in the sacrificial cladding was obtained. The results reveal the shock wave propagation characteristics in the sacrificial cladding. Two parameters, the attached mass and the strength of blasting load, are very important for the cellular sacrificial cladding design. Comparison of the sacrificial cladding structure designs based on the rigid-perfectly plastic-locking (R-PP-L) model and the R-PH model was presented and the applicable conditions of the two shock models were given. Finally, a cell-based finite element model using 3D Voronoi technology was employed to verify the design criteria of the cellular sacrificial cladding structure based on the R-PH model.

2014, 46(6): 825-833. doi: 10.6052/0459-1879-14-187

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DESIGN AND APPLICATIONS OF PIEZOELECTRIC CRYSTALS TRANSDUCER IN DYNAMIC EXPERIMENTS

Lu Fangyun, Li Junling, Zhao Pengduo, Cui Yunxiao, Wen Xuejun

Various piezoelectric crystals are widely used in many fields such as electronics industry, information transmission to achieve energy conversion, frequency control or as sensors and so on. With the unique piezoelectric properties and high frequency response, piezoelectric crystals have been used as force transducer in high strain-rate experiments to test dynamic stresses. Among them, quartz crystal has been used in split Hopkinson pressure bars (SHPB) for axial stress measurement, and in gas gun experiments as the shock wave pressure transducer. Meanwhile, with the anisotropic properties, it is possible to design a special rotated cut direction for the crystals to get a required piezoelectric response to selected stress. In this paper, we propose a design of shear transducer in split pressure-shear Hopkinson bars (SHPSB), by analyzing the wave propagation characteristics with a desired pure vibration mode in anisotropic crystals, and the basic principles of piezoelectric effect with independent response to the shear stress. Two typical shear transducers, which are made of 17.705° rotated Y-cut quartz and 165.44° rotated Y-cut lithium niobate respectively, are achieved finally.

2014, 46(6): 834-842. doi: 10.6052/0459-1879-14-162

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USING LAPLACE TRANSFORM TO SOLVE THE VISCOELASTIC WAVE PROBLEMS IN THE SHPB EXPERIMENTS

Zheng Yuxuan, Chen Liang, Zhou Fenghua, Wang Lili

In relation to the dynamic tests of materials, the approach to solve the viscoelastic wave propagations in split Hopkinson pressure bar (SHPB) tests was summarized. By conducting Laplace transform, the governing partial differential equations were transformed to ordinary differential equations for the image functions, which were solved analytically with suitable boundary equations. Inversely transforming these image functions gives the results of the stress, velocity, and strain in the bar. A wave problem are analyzed to evaluate the internal stress distributions in a viscoelastic specimen occurred in SHPB tests. The problem was solved numerically by way of numerical inverse Laplace transform. A special case when the specimen is pure elastic was solved analytically, giving the exact solution to the problem of elastic wave propagation in a sandwich elastic media.

2014, 46(6): 843-852. doi: 10.6052/0459-1879-14-002

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INVESTIGATION OF PLASMA DAMAGE PROPERTIES GENERATED BY HYPERVELOCITY IMPACT

Ning Jianguo, Li Jianqiao, Song Weidong

Based on the thermodynamics, a group of physical equations describing the relationship between the system internal energy and the electron density of hypervelocity impact generated plasmas were derived by combining with the chemical reaction rate equation. This group of equations was solved by a self-developed 2D SPH (Smoothed Particle Hydrodynamics) code to calculate the plasmas generated in the simulations of hypervelocity impacts in order to achieve the simulation of the generated plasmas. Then an aluminum projectile impact on double plates was numerically investigated and the results were compared with some experimental results. After accounting the charges generated by impacts on the front plate and the back plate respectively, it was found that the charges generated by the impact on the front plate were much less than thoses generated by the impact of first debris cloud on the back plate. Another simulation under the same condition except for the exchange of the two plates was conducted and the result showed that the plasma charges generated by the impact of debris cloud on the back plate in this simulation were less than that in the previous simulation but the plasma charges generated by the impact on the front plate in this simulation were more than that in the previous simulation. From these simulations, it could be concluded that the plasma charges generated by hypervelocity impact were not only related to the projectile mass and the impact velocity but also closely dependent on the thickness of the thin plate. The collision between the debris cloud and the second target generated more charges than the impact on the single target by the projectile. The impact on double plates increased the generation rate of the plasma and electromagnetic damage to the spacecraft.

2014, 46(6): 853-861. doi: 10.6052/0459-1879-14-058

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NUMERICAL INVESTIGATION ON FLOW-INDUCED VIBRATION OF TWO CYLINDERS IN TANDEM ARRANGEMENTS AND ITS COUPLING MECHANISMS

Ji Chunning, Chen Weilin, Huang Jilu, Xu Wanhai

Flow-induced vibration of two circular cylinders arranged in tandem at Re=100 is numerically investigated. The mass ratio of the cylinders is 2.0 and the center to center spacing ratio of the cylinders varies from 2.0 to 5.0. Two scenarios are considered: (a) the downstream cylinder is allowed to vibrate freely in the cross-flow direction while the upstream is fixed; (b) both cylinders are allowed to vibrate freely in the cross-flow direction. Results show that no matter the upstream cylinder is fixed or not, the transverse vibration amplitude of the downstream cylinder is obviously larger than an isolated one. For Scenario (a), the transverse amplitude of the downstream cylinder is larger than that of Scenario (b), which can be attributed to the fact below. When both cylinders vibrate freely, a significant "mutual-adjusting" happens between the wake of the upstream cylinder and the vibration of the downstream one, which intensifies the interaction between the two cylinders. We also investigated the coupling mechanisms of the downstream cylinder vibration and the gap flow of Scenario (b) and found that the vibration amplitude of the downstream cylinder attains its maximum when the reattached shear layer from the upstream cylinder can completely pass through the gap.

2014, 46(6): 862-870. doi: 10.6052/0459-1879-14-118

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SIMULATION STUDIES OF VISCOSITIES OF Cu-H₂O NANOFLUIDS BASED ON COARSE GRAINING WATER MOLECULES

He Yuchen, Liu Xiangjun

Molecular dynamics simulation is an important approach to study the viscosity characteristics of nanofluids but its computation scale is huge. In this paper, the computation scale is significantly reduced by applying the Martini force field on water-based fluid and coarse-graining water molecules. The micromotion of copper nanoclusters in water-based fluid was simulated based on the equilibrium molecular dynamics. The viscosities of Cu-H₂O nanofluids were calculated through the Green-Kubo formula. The effects of fluid temperature, volume fraction, shape and size of the particles on the viscosities of Cu-H₂O nanofluids were studied, based on which the existing empirical formula of the viscosity of suspension was modified.

2014, 46(6): 871-878. doi: 10.6052/0459-1879-14-087

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DYNAMICAL BEHAVIORS OF DOUBLE CAVITATION BUBBLES UNDER ULTRASONIC HONING

Guo Ce, Zhu Xijing, Wang Jianqing, Cheng Quan, Liu Guodong

In order to investigate the cavitation mechanism under the effect of ultrasonic honing, based on the superposition principle of fluid velocity potential, the dynamic model of double cavitation bubbles in the grinding area was established with considering ultrasonic honing velocity and honing pressure. The effects of initial cavitation bubble radius, double cavitation bubbles distance, ultrasonic acoustic pressure, honing pressure and honing rotation speed on cavitation bubble dynamics in the grinding area were simulated numerically. The results indicated that considering the interactions between double cavitation bubbles, it can acquire obvious cavitation effect when the initial radius ratio of two bubbles was controlled to be less than 3 (or was less than 3). A higher ultrasonic acoustic pressure and lower honing pressure obtained can also perform a better cavitation effect when the difference among ultrasonic acoustic pressure, honing pressure and fluid static pressure was in the range of 0.66MPa to 1.89MPa. Increasing the honing rotation speed can lead to slightly decrease the duration of the cavitation bubble collapse. The numerical results were well verified indirectly by experiments that the surface roughness of the material was measured to describe the cavitation effect of ultrasonic honing.

2014, 46(6): 879-886. doi: 10.6052/0459-1879-14-108

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RESEARCH ON PRESSURE WAVE PROPAGATION CHARACTERISTICS IN THREE-PHASE FLOW DURING MANAGED PRESSURE DRILLING

Kong Xiangwei, Lin Yuanhua, Qiu Yijie

In this paper, considering the virtual mass force, resistance, gas solubility and gas slip velocity etc., a model for predicting transient pressure wave velocity in oil-gas-water is established on the basis of the two-fluid equations. The influx gas is regarded as gas phase, and the influx oil is regarded as liquid phase. Parameters of liquid phase, such as elastic modulus and density, are defined as the weighted sum of the parameters of gas phase and drilling fluid. With the help of computer programming, the model is solved by the small disturbance theory and semi-implicit finite difference mathematical method. Results show that the pressure wave velocity is decreased by as much as 498.59m/s when the gas influx rate at the bottomhole increases form 0.36m³/h to 3.6m³/h. Meanwhile, the pressure wave velocity shows a slowly decreasing tendency at the same oil influx rate increase, decreasing by 19.21m/s. As the back pressure increases from 0.1MPa to 9.0MPa, the pressure wave velocity has an increasing tendency at a maximum increase of 233.15m/s. At low frequencies range, an increasing calculation error of pressure wave velocity can be observed with the increases of angular frequency by neglecting virtual mass force. At high frequencies range, the calculation error keeps constant at 10.03% when the influence of virtual mass force is neglected.

2014, 46(6): 887-895. doi: 10.6052/0459-1879-14-093

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EFFECTIVE SPECIFIC HEATS OF SPHERICAL PARTICULATE COMPOSITES WITH INHOMOGENEOUS INTERPHASES

Zhang Zhenguo, Chen Yongqiang, Huang Zhuping

The effective thermoelastic properties of spherical particulate composites with inhomogeneous interphases are studied. Particular emphasis is put on discussing the influence of the radial distribution of the interphase properties on the effective specific heats. Firstly, the inhomogeneous interphase is modeled by multiple concentric layers and the material properties are assumed to be homogeneous in each layer. The composite-sphere model, in which an interphase layer is embedded between the matrix and inclusion, is applied to derive the effective bulk modulus, thermal expansion coefficient (CTE) and specific heats. Secondly, for the case that the interphase properties vary continuously along the radial direction, a set of differential equations are established to determine the effective themoelastic properties of the composites. When the distribution of the Young's modulus of the interphase follows a power law, the analytical expressions of the effective properties are obtained by solving the differential equations. The effective CTE predicted by the present model is in good agreement with the experimental data. It is found that the distribution of both the interphase elastic moduli and the interphase CTE have great effects on the effective specific heats; however, only the distribution of the interphase CTE has significant impacts on the effective CTE.

2014, 46(6): 896-904. doi: 10.6052/0459-1879-14-190

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A MECHANICS MODEL OF A MONOLAYER GRAPHENE BASED ON THE LENOSKY INTERATOMIC POTENTIAL ENERGY

Huang Kun, Yin Yajun, Qu Benning, Wu Jiye

In this paper, the equations of motion for a monolayer graphene are obtained by a continuum limit form of elastic energy of the Lenosky C-C covalent bond and Hamilton principle. Using the equations and Galerkin method the static bending of a rectangular monolayer graphene is investigated. It is found that the bending stiffness has a significant effect on the Mechanical Characteristics of the grapheme. The graphene may be described by a plate when the graphene size is small, but the effect of bending stiffness will quickly decrease accompanying the size increment of the graphene. When the short side dimension is greater than 10nm for a rectangular monolayer graphene, the bending stiffness may be neglected and a thin film model is a good agreement with the monolayer graphene.

2014, 46(6): 905-910. doi: 10.6052/0459-1879-14-076

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THE FATIGUE CONSTITUTIVE MODEL OF CONCRETE BASED ON MICRO-MESO MECHANICS

Ding Zhaodong, Li Jie

In this paper we focus on the explanation of concrete fatigue damage on micro-meso-scales. Base on the rate process theory, the physical meaningful expression of fatigue damage energy dissipation is built on meso-scale with considering the dynamic effect of water molecules in the fracture process zone. Combing with meso-stochastic fracture model, the fatigue damage evolution equation is acquired under the framework of macro-damage mechanics. The fatigue damage evolution curve and fatigue life under various loading levels in uniaxial tension are computed with numerical simulation and the comparisons with test results show that the model proposed here gives a correct description of fatigue damage evolution process of concrete.

2014, 46(6): 911-919. doi: 10.6052/0459-1879-14-041

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STUDY ON THE PARAMETER VALUE DOMAIN OF MACRO-MICRO CONSTITUTIVE MODEL

Qu Jie, Qin Wei, Jin Quanlin

Parameter identification of macro-micro coupled constitutive model is generally taken through inverse analysis. To make the identified result with high confidence level, the reasonable parameter value domain must be given. Based on the physical mechanism during dynamic recrystallization and the mathematical characteristics of the constitutive equations, a procedure to determine the value domain of the parameters is proposed, which are involved in a macro-micro coupled constitutive model considering dynamic recrystallization. Firstly, the detail of the viscoplastic constitutive model is given, and a six-step method for the determination of the parameter value domain is given based on the physical mechanism; secondly, the hot compression deformation of low alloy steel 300M is carried out under different combinations of temperatures and strain rates, the datum on true stress-strain curves and microstructures are obtained. Based on the proposed procedure and the corresponding experimental datum, the parameter value domain is given. At last, the model is locally improved based on the information obtained during the above procedure.

2014, 46(6): 920-930. doi: 10.6052/0459-1879-14-049

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AN ENERGY APPROACH TO RAPIDLY ESTIMATE FATIGUE BEHAVIOR BASED ON INTRINSIC DISSIPATION

Guo Qiang, Guo Xinglin, Fan Junling, Hou Peijun, Wu Chengwei

The process of fatigue damage accumulation is an energy dissipation process accompanied with temperature variation. Compared with the local temperature rise in fatigue process, intrinsic dissipation is a direct reflection of material energy change, is related to the material microstructure evolution more closely, and has more definite physical meaning to be taken as a fatigue indicator. Based on a one-dimensional double exponential regression of the specimen surface temperature rise, a calculation model of intrinsic dissipation is established in this paper. On this basis, an energy approach for rapid evaluation of fatigue behavior is proposed. Utilizing this energy approach, the fatigue behavior of FV520B stainless steel has been experimentally studied. The analyses and comparisons of experimental results prove the feasibilities and validities of the energy approach and calculation model.

2014, 46(6): 931-939. doi: 10.6052/0459-1879-14-139

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DYNAMIC MODELING OF MULTI-BODY SYSTEM BASED ON GAUSS'S PRINCIPLE

Liu Yanzhu

Based on the Gauss's principle of least constraint, the dynamic modeling of a multi-body system connected by an elastic cable with varied lengths and large deformation in gravitational field of the earth was proposed in this paper. The practical background of the topic is the release process of a tethered satellite. The Kirchhoff's method was applied to transform the deformation of the elastic cable to rotation of rigid cross section along the centerline of the cable. Since the local small deformation of the cable can be accumulated limitlessly along the arc-coordinate, the Kirchhoff's model is suitable to describe the super-large deformation of elastic rod. In present paper the Gauss's constraint function of the system of rigid-flexible bodies in gravitational field of the earth was derived, and the geometric constraint conditions concerning relative position of bodies in space were considered using the Lagrange's multipliers. Therefore the dynamical model of the system was established in the form of conditional extremum problem. Applying the approach of Gauss's principle the real motion of the system can be obtained by the variation method directly through seeking the minimal value of constraint function without differential equations. The unified form of the model does not changed for different topologic constructions of the system, and it is unnecessary to distinct the tree system or system with loops. In the case of multi-body system with automatic control, the dynamic analysis can be combined with the optimization for different technique objectives.

2014, 46(6): 940-945. doi: 10.6052/0459-1879-14-143

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ANALYTICAL SOLUTION FOR ROTATIONAL RUBBING PLATE UNDER THERMAL SHOCK

Kou Haijiang, Yuan Huiqun, Zhao Tianyu

The analysis method is developed to obtain dynamic characteristics of the rotating cantilever plate with thermal shock and tip-rub. Based on the variational principle, equations of motion are derived considering the differences between rubbing forces in the width direction of the plate. The transverse deformation is decomposed into quasi static deformation of the cantilever plate with thermal shock and dynamic deformation of the rubbing plate under thermal shock. Then deformations are obtained through the calculation of modal characteristics of rotating cantilever plate and temperature distribution function. Special attention is paid to the influence of tip-rub and thermal shock on the plate. The results show that tip-rub has the characteristics of multiple frequency vibrations, and high frequency vibrations are significant. On the contrary, thermal shock shows the low frequency vibrations. The thermal shock makes the rubbing plate gradually change into low frequency vibrations. Because rub-induced vibrations are more complicated than those caused by thermal shock, tip-rub is easier to result in the destruction of the blade. The increasing friction coefficient intensifies vibrations of the rubbing plate. Minimizing friction coefficients can be an effective way to reduce rub-induced damage through reducing the surface roughness between the blade tip and the inner surface of the casing.

2014, 46(6): 946-956. doi: 10.6052/0459-1879-14-075

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DEPLOYMENT DYNAMICS OF FLEXIBLE SOLAR ARRAYS CONSIDERING FRICTIONAL JOINT

Duan Liucheng, Li Haiquan, Liu Xiaofeng, Cai Guoping

The deployment and locking of solar arrays of a free-floating spacecraft is studied in this paper. The rigid-flexible coupling dynamic model for describing the deployment and locking process is established using the Jourdain's velocity variational principle and the approach of forward recursive formulation. The contribution of joint friction to the dynamic equation of the system is derived based on the virtual power principle. The 3-D bristle friction model is introduced to study the influence of joint friction on the deployment dynamics of solar arrays. The validity of the proposed model is verified through the comparison of simulation results with those using the commercial software ADAMS and NASTRAN, and this model is available for predicting the deployment process of solar arrays and the attitude motion of spacecraft.

2014, 46(6): 957-970. doi: 10.6052/0459-1879-14-152

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QUADRILATERAL 4-NODE QUASI-CONFORMING PLANE ELEMENT WITH INTERNAL PARAMETERS

Wang Changsheng, Qi Zhaohui, Zhang Xiangkui, Hu Ping

A 4-node quadrilateral quasi-conforming plane element with internal parameters was proposed under the framework of quasi-conforming technique. New displacement functions with internal parameters can be added to the serendipity element Q4 to construct new isoparametric element. The explicit stiffness matrix of quasi-conforming element QC6N makes it more efficient. The numerical tests and comparisons with other 4-node isoparametric elements suggest that the present elements are more accuracy and less sensitive to the mesh distortion.

2014, 46(6): 971-976. doi: 10.6052/0459-1879-14-167

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STUDY ON THE RELATIONSHIP BETWEEN IGNITION DELAY TIME AND GASEOUS DETONATION CELL SIZE

Zhang Wei, Liu Yunfeng, Jiang Zonglin

In this paper, the intrinsic relationships between ignition delay times and the detonation cell size are analyzed, simulated from two one-step chemical kinetic models and one detailed chemical kinetic model. Ignition delay time for mixtures of hydrogen and air at 0.1MPa and 1.01MPa over the temperature range 800K to 1500K is investigated. The results demonstrate that the ignition delay time for one-step chemical kinetic model is independent of pressure, and linearly correlated with the initial temperature. The ignition delay time for the detailed chemical kinetic model is dependent of pressure, and is not linearly correlated with the initial temperature. However, in the inflection zone and the low temperature zone, the CFD results are 3 orders of magnitude smaller than the theoretical values. The CFD values of the ignition delay time differ from the theoretical ones by a factor as large as 10³. The detonation cell size simulated by all the chemical models is smaller than the experimental results, and the ignition delay time is proportional to the cell size. The detonation simulation results show that the longer the ignition delay time, the bigger the detonation cell size. The period of triple-point is almost equal to the ignition delay time of the gas behind the incident shock wave. Ignition delay time is a key parameter in detonation initiation and propagation.

2014, 46(6): 977-981. doi: 10.6052/0459-1879-14-046

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A SIMPLISTIC ANALYTICAL MODEL OF PERMEABILITY FOR OPEN-CELL METALLIC FOAMS

Yang Xiaohu, Bai Jiaxi, Lu Tianjian

Based on a generalized tortuosity model and a cubic unit cell topology, an analytical model is developed for predicting the permeability of open-cell metallic foams. The present model has a simple form and requires no fitting or empirical parameters. It is capable of analytically predicting the permeability of open-cell foams over a wide range of porosities (0.55～0.98) and pore densities (5～100 PPI), with good agreement with experimental data. Results demonstrate that the flow tortuosity determined by algorithm branching method enables faithfully capturing the behavior of fluid flow across open-cell metallic foams. Further, the modification made by open pore rate successfully extends the present permeability model from fully-open foams to semi-open ones.

2014, 46(6): 982-986. doi: 10.6052/0459-1879-14-115

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THIRD-ORDER GENERALISED BEAM THEORY AND CALCULATION METHOD

Zhao Rujiang

First-order Generalised Beam Theory (GBT) analysis can be used to describe the behaviour of prismatic structures by using deformation functions for bending, torsion and distortion in ordinary uncoupled differential equations. In second-order GBT, the differential equations then are involved with the effect of deviating forces. By derived the virtual works of two membrane stress terms into the GBT system, we can obtain the complete expansions of the third order GBT equation in the form of a series of large discretized iterated functions, which can be converted to sets of tangent stiffness matrices for further numerical analyses. By introducing the membrane stresses as the third order terms ^ijrkv_σ and ^ijrkv_τ and using advanced numerical techniques to find a complete solution, the third-order Generalised Beam Theory becomes a rigorous and efficient numerical tool to investigate large deflection behaviours in post-buckling of thin-walled structures.

2014, 46(6): 987-993. doi: 10.6052/0459-1879-14-033

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REVIEW OF THE FIRST NATIONAL SYMPOSIUM ON BIOMECHANICS FOR YOUNG SCHOLARS

Zhang Yan, Lou Jizhong, Xu Xianghong, Zhan Shige

This paper brief introduced the first national symposium on biomechanics for young scholars.

2014, 46(6): 994-998.

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