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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,China {3. of applied mechanics and biomedical Engineering,taiyuan university of technology,taiyuan 03.02.,China State Key Laboratory of Explosion Science and technology Beijing Institute of Technology Beijing China institute of applied {2. and {3. 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

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 {2. of technology,Beijing 100081,China {3. of applied mechanics and biomedical Engineering,taiyuan university of technology,taiyuan 03.02.,China 3.Labroratory for Shock Wave and Detonation Physics Research,{2. of Fluid Physics,CAEP,Mianyang 610059,China State Key Laboratory of Explosion Science and technology Beijing Institute of Technology Beijing China institute of applied {2. and {3. 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

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 {2., Shanghai {3., Shanghai 2.0072. China 2. Department of Building Engineering, Xi’an {3. of technology, Xi’an 710048, China Shanghai institute of applied Mathematics and {2. 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.

Three-dimensional configurations of organic/inorganic hybrid nanostructural blocks (I).A quantum mechanical investigation for ladder-like structure of vinylsilsesquioxane

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Science China Chemistry 2004年第5期47卷 388-395页

作者： ZHANG Xingwen1,2. HU Lijiang1, HUANG Yudong1, SUN Dezhi2.& SUN Yi3.1. Department of applied Chemistry,Harbin {2. of {2., HUANG Yudong, Harbin 150001, China 2. Department of Environmental Engineering, Harbin {2. of {2., Harbin 150001, China 3. Department of Experimental mechanics,Harbin {2. of {2., Harbin 150001, China Dept. of applied Chem. Harbin Inst. of Technol. Harbin 150001 China Dept. of Environ. Eng. Harbin Inst. of Technol. Harbin 150001 China Dept. of Experimental Mech. Harbin Inst. of Technol. Harbin 150001 China

The organic/inorganic hybrid nanostructural vinylsilsesquioxanes (VSSO) were prepared from the hydrolytic condensation of vinyltrimethoxysilane (VMS). The proposed formu- las of VSSO were assigned with standard spectroscopic techniques, FTIR, NMR (1H, C and 13.2.Si) and MALDI-TOF MS, and a generic formula of the SSO, Tn(OH)x(OR’)y(x, y = 0, 1, 2.; n = 1, 2.; T = RSiO1.5 ?(x+y)/2.). Geometric parameters (Si-O and Si-C bond lengths, Si-O-Si and O-Si-O bond angles) and total energies of the multi-structures of VSSO were calculated by a quantum mechanical investigation and molecular symmetries. According to the results of the calculation, most molecules had stabler ladder structures than the cage isomers, therefore, the most probably reasonable and optimum structure of the VSSO system was the ladder type.

关键词： vinyltrimethoxysilane (VMS), silsesquioxanes (SSO), sol-gel process, quantum mechanical calculation, MNDO.

Two-dimensional simulation of Poiseuille-Rayleigh-Bénard flows in binary fluids with Soret effect

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Progress in Natural Science:Materials International 2007年第12期17卷 1389-1396页

作者： Hu Jun1 and Yin Xieyuan2.1. institute of applied Physics and Computational Mathematics, Beijing 100088, China 2. Department of Modern {2., {3. of Science and technology of China, Hefei 2.3}02., China) institute of applied Physics and Computational Mathematics Beijing 100088 China Department of Modern mechanics University of Science and Technology of China Hefei 230027 China

Poiseuille-Rayleigh-Bénard flows in binary fluids with Soret effect are directly simulated by a mixed finite element method. A temperature perturbation is used as an initial disturbed source for the basic parallel flows. The whole spatio-temporal evolution of the binary fluid flows is exhibited: initially only the disturbed mode with the wavenumber k=π is amplified while others are damped, and continuously the amplified mode grows further and the nonlinear effect becomes important; after a nonlinear evolution transition the flow system evolves finally into a periodic right traveling wave.

关键词： Poiseuille-Rayleigh-Bénard flow Soret effect through-flow.

A NEW CONTINUUM TRAFFIC MODEL WITH THE EFFECT OF VISCOSITY

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Journal of Hydrodynamics 2011年第2期23卷 164-169页

作者： SONG Tao LI Xing-li KUANG Hua DONG Li-yun Shanghai institute of applied Mathematics and {2. Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai University Shanghai 200072 China School of applied Science Taiyuan University of Science and Technology Taiyuan 030024 China College of Physics and technology Guangxi Normal University Guilin 541004 China

Through considering the connection between microscopic car-following model and macroscopic continuum model, a new viscous vehicular flow model is proposed, in which the viscosity coefficient is determined by a more realistic constitutive relationship between averaged reaction time of drivers and the car density. Further analysis indicates that two traffic sound speeds in this viscous model may determine the existence and the stability of traveling wave solutions with an analytical method.

关键词： viscosity continuum traffic model reaction time traffic sound speed traveling wave

A study of two-dimensional magnetic polaron

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Science China(Physics,mechanics & Astronomy) 2006年第4期49卷 421-429页

作者： LIU Tao1, ZHANG Huaihong1, FENG Mang1,2.& WANG Kelin1,3.1. School of Science, Southwest university of Science and {2., Mianyang 62.010, China 2. Wuhan {2. of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 43.070, China 3. Department of Modern Physics, university of Science and {2. of China, Hefei 2.0}02., China School of Science Southwest University of Science and Technology Mianyang China Wuhan institute of Physics and Mathematics Chinese Academy of Sciences Wuhan China Department of Modern Physics University of Science and Technology of China Hefei China

By using the variational method and anneal simulation, we study in this paper the self-trapped magnetic polaron (STMP) in two-dimensional anti-ferromagnetic material and the bound magnetic polaron (BMP) in ferromagnetic material. Schwinger angular momentum theory is applied to changing the problem into a coupling problem of carriers and two types of Bosons. Our calculation shows that there are single-peak and multi-peak structures in the two-dimensional STMP. For the ferromagnetic material, the properties of the two-dimensional BMP are almost the same as that in one-dimensional case; but for the anti-ferromagnetic material, the two-dimensional STMP structure is much richer than the one-dimensional case.

关键词： self-trapped magnetic polaron, bound magnetic polaron, impurity potential, anti-ferromagnet.

ON THE GENERALIZED PLK METHOD AND ITS APPLICATIONS

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Acta Mechanica Sinica 1990年第2期6卷 111-118页

作者： Dai Shiqiang (Shanghai institute of applied Mathematics and {2.,Shanghai {3. of technology) Shanghai institute of Appl ied Mathematics and mechanics Shanghai University of Technology Shanghai China

In this paper,we propose a generalized form of the PLK *** solve weakly nonlinear prob- lems,in straining the related coordinates ,we choose a kind of transformations including nonlinear functionals of de- pendent variables to linearize asymptotically the original problems,and give more perfect asymptotic solutions with the first-term approximation and the derived *** analysis for some practical examples shows that the generalized method is straightforward and effective and might be applied to more complicated nonlinear problems.

关键词： straining of coordinates asymptotic solution asymptotic linearization

Parameter identification theory of a complex model based on global optimization method

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Science China(Physics,mechanics & Astronomy) 2008年第11期51卷 1722-1732页

作者： QU Jie1, JIN QuanLin2.& XU BingYe3.1 College of Automotive Engineering, South China university of {2., Guangzhou 510640, China 2.Beijing Research {2. of Mechanical and Electrical {2., Beijing 100083. China 3.Department of Engineering mechanics, Tsinghua university, Beijing 100084, China College of Automotive Engineering South China University of Technology Guangzhou China Beijing Research institute of Mechanical and Electrical technology Beijing China Department of Engineering mechanics Tsinghua University Beijing China

With the development of computer technology and numerical simulation technology, computer aided engineering (CAE) technology has been widely {3. to many fields. One of the main obstacles, which hinder the further application of CAE technology, is how to successfully identify the parameters of the selected model. An elementary framework for parameter identification of a complex model is provided in this paper. The framework includes the construction of objective function, the design of the optimization method and the evaluation of the identified results, etc. The parameter identification process is described in this framework, taking the parameter identification of the superplastic constitutive model considering grain growth for Ti-6Al-4V at 92.°C as an example. The objective function is the weighted quadratic sums of the difference between the experimental and computational data for the stress-strain relationship and the grain growth relationship; the designed optimization method is a hybrid global optimization method, which is based on the feature of the objective function and incorporates the strengths of genetic algorithm (GA), the Levenberg-Marquardt algorithm and the augmented Gauss-Newton algorithm. The reliability evaluation of parameter identification result is made through the comparison between the calculated and experimental results and between the theoretical values of the parameters and the identified ones.

关键词： constitutive model parameter identification theory inverse analysis global optimization