Assessing the predictive capability of two‐phase models for the mechanical behavior of alumina/epoxy nanocomposites

A review of analytical modeling of particulate reinforcement is made as a prelude to the problem of microstructural inhomogeneity in nanocomposite materials. Noting the inevitability of dispersion nonuniformity, and variations in agglomerate morphology and filler‐matrix interaction, the need to question the application of such models to novel materials arises. Employing the mechanical properties of alumina/epoxy nanocomposites, with known dispersion characteristics, an evaluation of the predictive capability of various models for Young's modulus, strength, and failure strain is made. Comparison between models is accompanied by a discussion of the parameters used in the fitting of macroscopic behavior to microstructural features. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 869–879, 2005     

层次约束结构的虚拟装配建模技术

为了解决虚拟环境下装配建模在信息完备性和模型复杂性等方面的问题,提出了一种基于层次约束结构的虚拟装配模型.该模型分为产品层、部件层、零件层、特征层、几何面层和面片层来表达,不同层元素之间存在层次映射关系,同一层元素之间存在约束关系.通过CAD系统和虚拟装配系统之间的数据转换,实现了虚拟装配模型的生成算法,并给出了根据虚拟装配模型生成的虚拟装配场景图的结构.基于层次约束结构的虚拟装配模型具有信息表达完备,信息集成度高,满足实时性要求等优点,同时还能与CAD系统和虚拟装配场景图实现集成.实例验证了虚拟装配建模的有效性.     

虚拟样机技术在门座起重机设计中的应用

分析门座起重机设计的现状,结合虚拟样机技术、参数化建模技术实现门座起重机的三维参数化建模,并应用虚拟装配技术生成整机系统的虚拟样机模型;通过对门座起重机虚拟样机的建模分析,为起重机有限元动力学分析提供精确的模型,减少设计开发成本.     

数控加工三维场景几何建模技术研究

讨论了基于构件技术的数控加工三维场景建模技术,并以OpenGL和Visual C++6.0为开发平台,开发出一个基于STL文件格式的建模系统.     

Image-based extended finite element modeling of thermal barrier coatings

Further advances in Thermal Barrier Coating (TBC) design are linked with the evolution of numerical models for TBCs. The present paper, therefore, enhances the idea of a currently available FEM package (OOF) that has been designed for microstructural level simulations. The approach of Extended FEM (XFEM) is incorporated in an in-house developed program to account for the existence of cracks in TBCs; both for stress-strain analysis and for heat transfer analysis. The new XFEM program is then employed to carry out the analyses of a YSZ deposit and a multilayered TBC to predict the effective Young's moduli, the overall thermal conductivities, and to assess the fracture behavior of the coating.     

A computational fluid dynamic analysis of gas and particle flow in flame spraying

The flame spraying process, which is a common industrial thermal spraying application, has been analyzed by means of three-dimensional computational fluid dynamics (CFD) simulations. The process used at the Volvo Aero Corporation for the coating of fan and compressor housings has been modeled. The process uses the Metco 6P torch (Metco, Westbury, NY), which ejects a mixture of acetylene and oxygen at high speed through a ring of 16 orifices to form the flame. A stream of argon gas flowing through an orifice in the center of the ring carries a powder of nickel-covered bentonite through the flame to the spray substrate. The torch is cooled by a flow of air through an outer ring of 9 orifices. The simulation emulated reality closely by including the individual inlets for fuel, cooling air, and injected particles. The gas combustion was simulated as a turbulent, multicomponent chemically reacting flow. The standard, two-equation k-ε turbulence model was used. The chemical reaction rates appeared as source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions and the Magnussen and Hjertager eddy dissipation model. The first simulations included several intermediate chemical substances whose predicted concentration agreed favorably with measurements. Later, more simplified simulations incorporated only the global chemical reaction involving the initial and the final products, with corrections to the thermal properties being made to account for the missing intermediaries. The gas velocity and temperature fields predicted by the later simulations compared satisfactorily to those predicted by the earlier, more elaborate, ones. Therefore, the final simulations, which incorporated injected particles, were conducted employing the simplified model with only the global reaction. An in-house finite difference code was developed to calculate particle properties. Allowance was made for elliptical shapes, phase changes, and internal heat transfer with regard to the composite material. The particle velocities and temperatures predicted by the final simulations compared fairly well with experimental results obtained with the optical DPV2000 system.     

Numerical modeling of high-temperature corrosion processes

Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element may form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.     

Knowledge and Belief: Some Clarifications

The notions of knowledge and belief play an important role in philosophy. Unfortunately, the literature is not very consistent about defining these notions. Is belief more fundamental than knowledge or is it the other way around? Many accounts rely on the widely accepted strategy of appealing to the intuition of the reader. Such an argumentative methodology is fundamentally flawed because it lets the problems of common sense reasoning in through the front door. Instead, I suggest that philosophical arguments should be based on formal-computational models to (a) reduce the ambiguities and uncertainties that come with intuitive arguments and reasoning, and (b) capture the dynamic nature of many philosophical concepts. I present a model of knowledge and belief that lends itself to being implemented on computers. Its purpose is to resolve terminological confusion in favor of a more transparent account. The position I defend is an antirealist naturalized one: knowledge is best conceived as arising from experience, and is fundamental to belief.