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Multimaterial Lattice Structures With Thermally Programmable Mechanical Behaviors
Hang YANG, Li MA
, Available online  , doi: 10.21656/1000-0887.430104
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Abstract:
Traditional lattice structures usually maintain their mechanical properties throughout their lifetime. Designing and manufacturing intelligent materials with environmental adaptability, programmable sense and responses to external changes (such as light, pressure, solution, temperature, electromagnetic field and electrochemical reaction), shape transformation, mode conversion and performance regulation in space and time, are still important scientific challenges in the field of artificial materials. In this paper, multimaterial lattice structures with thermally programmable mechanical responses were proposed by means of polymer materials with disparate glass transition temperatures and temperature dependencies, and through reasonable design of the spatial distribution of the materials. By theoretical analysis combined with finite element simulation, the effects of the relative stiffnesses of constitute materials on Poisson's ratios, deformation modes and structural stability of the multimaterial lattice structures, were studied. The elastic constants, crushing responses and structural stability of multimaterial lattice structures were regulated by temperature control, consequently the multimaterial lattice structures were endowed with giant thermal deformation, hyperelasticity and shape memory effects. This paper opens up new avenues for the design and manufacture of adaptive protection equipment, biomedical devices, aerospace morphing structures, flexible electronic devices, self-assembly structures and reconfigurable soft robots.
Reduced-Scale Experiment Study on the Protective Mechanism of Foam Coating Against Underwater Explosion Bubble Jet
Zhipeng DU, Lei ZHANG, Yong CHEN, Hongxing HUA
, Available online  , doi: 10.21656/1000-0887.420367
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Underwater explosion poses a serious threat to underwater structures. Flexible coatings or sandwich plates can reduce the underwater explosion impact responses of underwater structures, and make a research hotspot. Previous studies focused on the protective mechanism of the coating against shock waves, which is suitable for underwater explosion at a long distance. Besides the shock wave, the high-speed water jet towards the structure produced by explosion bubble collapse, is more deadly in the short-distance underwater explosion. In view of this situation, based on the dimensional principle, the reduced-scale similarity relationship was deduced. Through the reduced-scale-model underwater explosion test, it is found that, the cavitation micro-bubble group on the surface of the foam coating interferes with the formation process of the explosion bubble collapse high-speed water jet. The protection mechanism of the foam coating against the underwater explosion bubble collapse water jet for coated steel plates was put forward.
The Low-Frequency Broadband Mechanism of Nonlinear Elastic Metamaterials With Gaps
Zhen LIN, Jiuhui WU
, Available online  , doi: 10.21656/1000-0887.430103
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A new formation mechanism of the low-frequency broadband within gapped nonlinear local resonance structures was revealed based on the nonlinear chaos theory, and a novel concept for designing nonlinear local resonant structures with small gaps was further proposed. Due to the small gaps, the nonlinear chaos phenomenon occurs in the local resonance system, which can change the spectrum structure in vibration noise successfully, and the linear spectral energy greatly weakens and a continuous broad spectrum forms after chaotic motion, to effectively isolate the low-frequency spectrum. Most importantly, the finite element results show that, the nonlinearity of the small gap indeed leads to the low-frequency band-gap within the nonlinear local resonance. Therefore, the new idea for designing the nonlinear local resonance structure makes a new way to the development of local resonant elastic metamaterials, and the formation mechanism of low-frequency band-gap based on the nonlinear chaos theory lays a very important theoretical basis for vibration and noise reduction.
Anti-Plane Problem of Collinear Interface Cracks Emanating From a Circular Hole in One-Dimensional Hexagonal Quasicrystal Bi-Material
Bingcai ZHANG, Shenghu DING, Laiping ZHANG
, Available online  , doi: 10.21656/1000-0887.420202
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The anti-plane problem of asymmetric collinear interface cracks emanating from a circular hole in one-dimensional hexagonal quasicrystal bi-material is studied. Using Stroh formula and complex function method, the complex potential functions under the coupling action of phonon field and phason field are obtained. The analytical expressions of stress intensity factor (SIF) and energy release rate (ERR) at the crack tip are given. The effects of the radius of the circular hole and the length of the crack on the SIF, and the effects of the coupling coefficient, the phonon field and the phason field stresses on the ERR are discussed. The results show that the SIF tends to be stable with the increase of the length of the right crack when the radius of the circular hole is constant. When the phason field stress takes a certain value, the ERR reaches the minimum, which indicates that the specific phason field stress can inhibit the crack growth.
Thermo-Mass Coupling Fractal Study of Wet Phase-Change Rough Porous Materials
Weiye GAO, Sai ZHANG, Jie ZHANG, Shiwang HU, Zhenyi WANG
, Available online  , doi: 10.21656/1000-0887.420328
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Abstract:
The complex internal structures and moisture states of porous materials are of great significance to heat and mass transfer, and their coupling heat and mass transfer processes widely exist in energy development and engineering heat insulation. Beyond the unilateral analysis of heat and mass transfer characteristics of porous materials under ideal conditions, the distribution parameters of porous channels, rough surface, wet states and phase-change were considered, and the fractal theory was used to deduce the expressions of the seepage coefficient and the coupling equivalent thermal conductivity of porous materials with wet phase-change rough surface. The results show that, the seepage coefficient is positively correlated with the area fractal dimension and the moisture saturation, and negatively correlated with the relative roughness and the tortuous fractal dimension. The coupling equivalent thermal conductivity is positively correlated with the seepage coefficient and the phase variable, but negatively correlated with the relative roughness. In addition, the phase variable and the gas expansion pressure difference caused by phase-change also have important effects on the coupling heat and mass transfer.
A Study on the Vortex-Induced Vibration Mechanism of Cantilever Cylinders Under Gas-Liquid Cross Flows
Hao YAN, Huliang DAI, Lin WANG, Qiao NI
, Available online  , doi: 10.21656/1000-0887.430065
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Aimed at vortex-induced vibration (VIV) of the submarine reconnaissance telescope lifting above the water surface, a theoretical model for VIV of a cantilever cylinder under the actions of 2 different cross flows, i.e. gas and liquid, was established. The effects of parameters such as the distribution ratio and the density ratio for these 2 fluids on VIV responses of the cylinder were studied. Based on the Galerkin technique and the Runge-Kutta algorithm, numerical results of the cylinder vibration responses were obtained. The results show that, the increase of the distribution ratio can widen the lock-in range of the cylinder. The peak amplitude of the cylinder increases first and then decreases with the distribution ratio. The amplitude reaches the maximum value with a distribution ratio of 0.5, and this maximum value will increase with the decrease of the density ratio. In addition, single-period and multi-period motions will occur with the change of the fluid distribution ratio. The present research provides a theoretical guidance for the design and analysis of the submarine reconnaissance telescope.
Global Existence of Solutions and Lower Bound Estimation of Blow-Up Time for Keller-Segel Chemotaxis Model
Yuanfei LI
, Available online  , doi: 10.21656/1000-0887.420109
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In this paper, we consider a macroscopic nonlinear Keller-Segel model for chemotactic cell migration, where the existence region of the model is bounded convex on $\varOmega\subset\mathbb{R}^N(N\geqslant2)$. The global existence of the solution on $\varOmega\subset\mathbb{R}^3$ is obtained by using the energy estimates method. The lower bounds of the blow-up time are proved when $N=3 $ and $N=2$.
Dynamic Analysis of Network Epidemic Model Based on the White Noise
Xiaochun CAO, Wenjun JING, Zhen JIN
, Available online  , doi: 10.21656/1000-0887.430009
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Based on the deterministic network infectious disease model, a stochastic network infectious disease model under the influence of white noise is established, and the existence and uniqueness of the global solution of the model is proved. Using the theory of stochastic differential equation, sufficient conditions for stochastic extinction and persistence of infectious diseases are obtained. The results show that white noise has a great impact on the transmission dynamics of infectious diseases on the network. White noise can effectively suppress the spread of infectious diseases, and large white noise can even make the original persistent infectious diseases become extinct. Finally, the theoretical results are verified by numerical simulations.
Study on Interfacial Fracture Behavior of Superconducting Thin Film/Substrate Structure Considering the Effect of Flux Flow
Jieying DING, Feng XUE, Xiaofan GOU
, Available online  , doi: 10.21656/1000-0887.420353
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Superconducting thin film is a kind of multilayer structure prepared by chemical coating. As a conductive functional structure material with excellent performance, its structural integrity is directly related to current-carrying capacity. During the preparation of superconducting thin films, it is hard to avoid the interface cracks between the superconducting layer and the metal substrate. In this case, along with the current-carrying operation, the strength of the interface crack in an external magnetic becomes a key problem. Therefore, based on the theory of flux through thin film and linear elastic fracture, an analytical model of the strength of the interface crack between the superconducting film and the substrate is established. The influence of viscous flux flow on the stress field and the energy release rate of the crack tip is obtained. The results show that the higher the flux flow velocity is, the greater the stress and energy release rate at the crack tip of the interface will be, which will lead to crack propagation at the interface. The results obtained in this paper are helpful for the analysis of interface cracks mentioned above.
Characterizations of Approximate Optimality Conditions for Fractional Semi-infinite Optimization Problems with Uncertainty
Xinyi FENG, Xiangkai SUN
, Available online  , doi: 10.21656/1000-0887.420248
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This paper is devoted to the investigation of a class of multi-objective fractional semi-infinite optimization problems with uncertain data. Firstly, a robust counterpart for the uncertain multi-objective optimization problem is introduced in terms of robust optimization method. And following the idea due to Dinkelbach, we associate the robust counterpart with a multi-objective optimization problem. Then, by using a scalarization method, its corresponding scalarization optimization problem is established. The relationship between robust solutions of the multi-objective optimization problem and that of its corresponding scalarization optimization problem is described. Finally, by using a robust type sub-differential constraint qualification, the robust optimality condition for approximate quasi-efficient solutions of the multi-objective fractional optimization problem is established.
Interlaminar Crack Propagation Analysis of ENF Specimen Based on Cohesive Zone Model
Jian DENG, Pengcheng XIAO, Zengxian WANG, Guangran SHAO, Tianjian LU
, Available online  , doi: 10.21656/1000-0887.430082
Abstract(48) HTML (28) PDF(7)
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Based on classical laminated plate theory and cohesive zone model, a theoretical model of general delamination cracked laminates is established for crack propagation of pure mode Ⅱ ENF specimen. Compared with the conventional beam theory, the proposed model fully consideres the softening process of the cohesive zone and introduced the nonlinear behavior of ENF specimens before failure. The predicted failure load is smaller than the beam theory and closer to the experimental data in literature. Compared with the beam theory with only fracture toughness considered, the proposed model can simultaneously analyze the influence of interface strength, fracture toughness and initial interface stiffness on the load-displacement curves in ENF tests. The results show that the interface strength mainly affects the mechanical behavior of specimens before failure, but has no influence on crack propagation. The fracture toughness is the main parameter affecting crack propagation, and the initial interface stiffness only affects the linear elastic loading section. The length of cohesive zone increases with the increase of fracture toughness and decreases with the increase of interface strength. The effect of interface strength on the length of cohesive zone is more obvious than fracture toughness. When the tip of the adhesive zone reaches the half-strength of the specimen, the length of the adhesive zone decreases to a certain extent.
Fractal Model of Thermal Dispersion Coefficient of Porous Media
Jie ZHANG, Sai ZHANG, Weiye GAO, Shiwang HU, Zhenyi WANG
, Available online  , doi: 10.21656/1000-0887.420314
Abstract(82) HTML (34) PDF(8)
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Thermal dispersion coefficient is an important parameter to characterize heat and mass transfer in porous media, which is related to the physical properties of fluid and the structure of porous media. The pore-throat structure model of fractal porous media was established, and the local head loss and velocity dispersion effect of fluid changing from turbulent state to laminar state at pore-throat structure were studied. The relationship of thermal dispersion coefficient was derived considering the influence of micropore-throat structure and velocity dispersion effect. The results showed that the thermal dispersion coefficient is directly proportional to the pore-throat ratio, the number of pore-throat structures and tortuous fractal dimension, and inversely proportional to the porosity and surface integral dimension. Further study showed that the pore throat ratio has a significant influence on velocity dispersion effect in the range of 1~150, and the fluid has local head loss at the pore throat structure, which leads to the enhancement of velocity dispersion effect and the increase of thermal dispersion coefficient.