Interaction of Supercavitating Strikers with Underwater Obstacles

Journal of Engineering Physics and Thermophysics - The interaction of supercavitating strikers with obstacles placed in water was investigated in a wide range of intersection angles. Several...     

Superfluid Properties of One-Component Fermi Gas with an Anisotropic p-Wave Interaction

We investigate superfluid properties and strong-coupling effects in a one-component Fermi gas with an anisotropic p-wave interaction. Within the framework of the Gaussian fluctuation theory, we determine the superfluid transition temperature T _c, as well as the temperature T ₀ at which the phase transition from the p _x -wave pairing state to the p _x +ip _y -wave state occurs below T _c. We also show that while the anisotropy of the p-wave interaction enhances T _c in the strong-coupling regime, it suppresses T ₀.     

Investigation of Elastoplastic Properties of Tungsten Carbide-Based Alloy Strikers in Interaction with a Steel Target by the Computational-Experimental Method

Journal of Engineering Physics and Thermophysics - A mathematical model has been constructed for the behavior of a tungsten carbide alloy on the basis of TC8 (tungsten carbide, 92%; cobalt, 8%) and...     

Modeling of the Interaction of an Aqueous Electrolyte with Metals: Molecular-Dynamic Approach

We develop a computer model of the electrochemical behavior of a metal-electrolyte interface based on the joint application of the MNDO semiempirical quantum-chemical and molecular-dynamic methods. We consider the evolution of metal-environment systems and study in detail the thermodynamic and kinetic features of establishing the adsorption-desorption equilibrium for the cluster systems FeCu-aqueous electrolyte and FeCr-aqueous electrolyte. We calculate the following electrolytic micropotentials: absolute for a hydrogen electrode and relative for copper, zinc, iron, α-brass, and iron-chromium alloy, which are in good agreement with experimental data.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 5, pp. 7–12, September–October, 2004.     

Measurement and Modeling of the Emittance of Silicon Wafers with Anisotropic Roughness

The unpolished surface of crystalline silicon wafers often exhibits non-Gaussian and anisotropic roughness characteristics, as evidenced by the side peaks in the slope distribution. This work investigates the effect of anisotropy on the emittance. The directional-hemispherical reflectance of slightly and strongly anisotropic silicon wafers was measured at room temperature using a center-mount integrating sphere. A monochromator with a lamp was used for near-normal incidence in the wavelength region from 400–1000 nm, and a continuous-wave diode laser at the wavelength of 635 nm was used for measurements at zenith angles up to 60°. The directional emittance was deduced from the measured reflectance based on Kirchhoff’s law. The geometric-optics-based Monte Carlo model that incorporates the measured surface topography is in good agreement with the experiment. Both the experimental and modeling results suggest that anisotropic roughness increases multiple scattering, thereby enhancing the emittance. On the other hand, if the wafer with strongly anisotropic roughness were modeled as a Gaussian surface with the same roughness parameters, the predicted emittance near the normal direction would be lower by approximately 0.05, or up to 10% at a wavelength of 400 nm. Comparisons also suggest that the Gaussian surface assumption is questionable in calculating the emittance at large emission angles with s polarization, even for the slightly anisotropic wafer. This work demonstrates that anisotropy plays a significant role in the emittance enhancement of rough surfaces. Hence, it is imperative to obtain precise surface microstructure information in order to accurately predict the emittance, a critical parameter for non-contact temperature measurements and radiative transfer analysis.     

Wave Interaction with Defects in Pressurised Composite Structures

There exists a great variety of structural failure modes which must be frequently inspected to ensure continuous structural integrity of composite structures. This work presents a finite element (FE) based method for calculating wave interaction with damage within structures of arbitrary layering and geometric complexity. The principal novelty is the investigation of pre-stress effect on wave propagation and scattering in layered structures. A wave finite element (WFE) method, which combines FE analysis with periodic structure theory (PST), is used to predict the wave propagation properties along periodic waveguides of the structural system. This is then coupled to the full FE model of a coupling joint within which structural damage is modelled, in order to quantify wave interaction coefficients through the joint. Pre-stress impact is quantified by comparison of results under pressurised and non-pressurised scenarios. The results show that including these pressurisation effects in calculations is essential. This is of specific relevance to aircraft structures being intensely pressurised while on air. Numerical case studies are exhibited for different forms of damage type. The exhibited results are validated against available analytical and experimental results.     

Experimental Observations and Computational Modeling of Fracturing in an Anisotropic Brittle Crystal (Sapphire)

The commonly used fracture criteria-maximum K_I, zero K_II, maximum hoop-stress, and maximum energy-release rate-predict similar fracture paths in isotropic materials, but not in anisotropic materials. In the general anisotropic case, the fracture path depends on the material-symmetry properties, the nature of the applied loads, and the overall geometry of the specimen. In addition, anisotropy in the material's resistance to fracturing plays a key role in defining crack initiation and its propagation path. Experiments are performed on notched specimens made from sapphire, a microscopically homogeneous and brittle single-crystal solid. The force required for fracture initiation is measured. The experimental measurements/observations are compared with the numerical results of the FEM simulations. A stress-based fracture parameter, is shown to be a good measure of the fracture criterion, where σ and E, respectively, are the tensile stress and Young's modulus in the direction normal to the cleavage plane, with surface energy γ , and R is a characteristic length, e.g., the notch radius. This parameter takes into account the effects of the surface energy of the corresponding cleavage plane, as well as the strength of the atomic bonds in the direction normal to the cleavage plane. More than two-thirds of the notched specimens fractured at the point and along a cleavage plane where A is maximum. The measurements of the applied force made it possible to quantitatively obtain a critical value for parameter A. Finally, experiments show that for the notched sapphire specimens the weakest family of cleavage planes, , are the fracture planes, although a few specimens fractured along non-cleavage planes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Multi-Scale Modeling of an Integrated 3D Braided Composite with Applications to Helicopter Arm

A study is conducted with the aim of developing multi-scale analytical method for designing the composite helicopter arm with three-dimensional (3D) five-directional braided structure. Based on the analysis of 3D braided microstructure, the multi-scale finite element modeling is developed. Finite element analysis on the load capacity of 3D five-directional braided composites helicopter arm is carried out using the software ABAQUS/Standard. The influences of the braiding angle and loading condition on the stress and strain distribution of the helicopter arm are simulated. The results show that the proposed multi-scale method is capable of accurately predicting the mechanical properties of 3D braided composites, validated by the comparison the stress-strain curves of meso-scale RVCs. Furthermore, it is found that the braiding angle is an important factor affecting the mechanical properties of 3D five-directional braided composite helicopter arm. Based on the optimized structure parameters, the nearly net-shaped composite helicopter arm is fabricated using a novel resin transfer mould (RTM) process.     

Modeling and Calculation of the Thermal Destruction of a Cylindrical Shell

An approximate analytical solution of the problem of nonlinear heat conduction in a cylindrical shell with allowance for the thermal destruction and removal of the material from the shell's surface as a result of the action of a hightemperature heat flux on it has been constructed. An example of numerical calculation has been given.     

On the Effects of Interacting Anisotropic Fibers on the Microbuckling in a Composite

An analysis of microbuckling in a composite with anisotropic fibers under compression is presented. The modelling accounts for the fiber interaction, the distinct difference in the properties of the fibers and the matrix, and also for the presence of the external boundary. Results are calculated for cases of perfect fiber-matrix bonding. It is demonstrated that the critical loading parameters can depend essentially both on the fiber anisotropy and the fiber interaction. These factors must be properly accounted for in order to get acceptable estimations of the critical loads.     

塑料包装多层复合阻隔技术的开发

为了提高塑料的阻隔性能,近年来,业界一方面在研究开发新型高阻隔性塑料,另一方面则是对现有的塑料包装材料进行改性。由于多层复合、共混、表面镀覆、表面PA、PDVC、EVOH或铝箔,内热封层为CPP,若不需要耐高温也可用PE,     

复合柔性结构航天器动力学建模研究

柔性航天器动力学建模的传统方法是采用混合坐标法,针对中心刚体带大型柔性附件类的航天器,这种方法在理论建模和工程应用方面都获得了极大的成功。在中心刚体加柔性附件类航天器柔性动力学研究成果基础上,通过计及柔性体与柔性体连接点间的复合位移变形,利用混合坐标法建立了复合柔性结构航天器动力学模型,其软件系统DASFA 2.0已初步用于工程分析设计。     

Modeling of Bonding at an Interface Crack

A mechanical and mathematical model is suggested for an interface crack with bonding in its end zones. Normal and shear bond tractions occurring under the action of the external loads are searched for by solving a system of two singular integrodifferential equations. The stress intensity factors at the crack tip are calculated taking the compensating action of the bonds into account. Energetic characteristics of the interface crack (the deformation energy release rate and the rate of the energy absorption by the bonds) are analyzed. A sensitivity analysis is performed of the force and energetic characteristics of the interface crack to the end zone size, bond compliance and limit stretching. This revised version was published online in July 2006 with corrections to the Cover Date.     

不同高阻隔复合膜在带有沟槽的真空绝热板上的适用性研究

为进一步提高真空绝热板的适用场所,从异形真空绝热板的发展趋势进行分析,重点研究了高阻隔复合膜对异形真空绝热板的影响,通过对比市面上主流的几款高阻隔复合膜,分析在带有沟槽的异形真空绝热板上使用的可行性,并通过导热系数等对比实验进一步验证,得出最佳膜材选择方案,从而为带有沟槽的真空绝热板量产化提供参考依据。     

高防潮阻隔性封套包装复合材料设计探讨

目的探讨柔性封套包装用高防潮阻隔性复合材料的设计与选材。方法首先通过对封套包装的功能作用原理进行分析,探讨封套复合材料的防潮阻隔性、使用性能、环境适应性及工艺性等设计内容与要求,然后从环境、材料等方面简要分析直接影响封套复合材料防潮阻隔性能的主要相关因素,并对材料结构设计、功能层材料选用等进行研究。结果总结分析了封套复合材料结构铺层设计、材料选用设计方法以及需要注意的事项。结论封套包装复合材料的性能设计、结构铺层设计及功能层材料选用,应以能够满足装备可靠封存防护要求为前提,同时兼顾其使用性和经济性。     

A Quantum Mechanical Treatment of the Vortex–Vortex Interaction in Anisotropic Superconductors

Using a new Hamiltonian of interaction [Int. J. Mod. Phys. B16, 4809 (1002); B17, 4763 (2003)], we calculate the vortex–vortex interaction energy in anisotropic superconductors. We present here the analytical formulae. The interaction energy has a minimum at a certain vortex–vortex distance. This distance decreases with the increase of the angle θ between the vortex line and the crystalline axis. Also, we calculate the elastic force and the nonharmonicity coefficients of the vortex lattice. Both coefficients decrease with increasing angle. Generally, the interaction energy decreases with the angle increase. Finally, we present the self-energy of a vortex in a lattice, the energy of a single isolated vortex and the lower critical field. Also, the surface of the vortex in the lattice has a form of a rosette with six petals, which are all equals for θ = 0 and become nonequals for θ ≠ 0. The surface of the first isolated vortex has a form of an oval for θ ≠ 0, and becomes a circle for θ = 0. PACS numbers: PACS 74.25.Qt.     

Prediction of Buckling-Mode Interaction in Composite Columns

Pultruded structural shapes are often used as columns of intermediate length, for which the global and local buckling loads are close. Interaction between the two buckling modes is accounted for in design by an empirical interaction constant. Theoretical/numerical prediction of such a constant is presented in this article. Stability theory is used to demonstrate the existence of buckling-mode interaction. The continuation method is used to study the imperfection sensitivity of the columns. A relationship between column imperfection and the interaction constant is established. Experimental results are presented to support the analysis.