On the Compliance Contribution Tensor for a Concave Superspherical Pore

Erosion and corrosion result in potential material loss. The erosion is a physical phenomenon but corrosion is chemical one. The study of these two phenomena, as functions of time and temperature, would lead to a better understanding of glass surface damage. Results allow one to determine the effects of immersion time, temperature of the water bath and residual stresses generated by Vickers indentation on the radial crack and topography of the imprint on the surface of a soda-lime silica glass. Water corrosion effects are different at the imprint corner and the radial crack tip as compared to edges and faces.     

On a Possible Approximation of Changes in Elastic Properties of a Transversely Isotropic Material due to an Arbitrarily Oriented Crack

The present paper addresses an approximate analytical model for contribution of an arbitrarily oriented circular crack into effective elastic compliance of a transversely isotropic material. We numerically examine the bounds of applicability of the hypothesis that change in elastic potential due to an arbitrarily oriented circular crack in a transversely-isotropic material can be approximated by the change calculated for a certain isotropic environment. In particular, we obtained that the error of such an approximation is less than 20% if the extent of anisotropy is moderate – the ratio of Young’s moduli in transverse and in-plane directions is less than 1.87. The obtained result can be used for development of a simple model for microcracked transversely-isotropic materials with mild-to-moderate extent of anisotropy.     

The Nature of Stress and Electric-displacement Concentrations around a Strongly Oblate Cavity in a Transversely Isotropic Piezoelectric Material

In this paper we explore the nature of stress and electric-displacement concentrations around a strongly oblate spheroidal cavity that possesses a finite dielectric permittivity. We start out from Eshelby’s general inclusion method but give specific account on the important class of piezoelectric ceramics whose structure is represented by the 6 mm symmetry. It is found that under axial electromechanical loading these concentrations are governed by a dimensionless parameter η, defined as (k₀/k₃₃)/(c/a), that involves the ratio of the dielectric permittivity of the medium inside the cavity k₀, to that of the transversely isotropic piezoelectric ceramic k₃₃, and the aspect ratio of the cavity c/a. When the medium inside the cavity is an impermeable one it is found that both the axial stress and axial electric displacement can have direct contribution to the concentration factors, but when the medium is a conducting one only the applied stress has an effect on it. Our analysis further indicates that it is the parameter η – not k₀/k₃₃ or c/a alone – that plays the key role here; when η< 0.01, the cavity can be effectively treated as an impermeable one, while for η> 100 it can be treated as a conducting case. Numerical results for several PZT ceramics suggest that under a pure tensile stress the ceramic tends to fracture on the equatorial plane, but under a pure electrostatic load it tends to develop radial cracks normal to the edge of the cavity.     

Parameter-Estimation Algorithms for Characterizing a Class of Isotropic and Anisotropic Viscoplastic Material Models

A number of robust, and computationally efficient, algorithms arepresented for the development of an overall strategy to estimate thematerial parameters characterizing a class of complex viscoplasticmaterial models (i.e., rate dependent plastic flow, nonlinear kinematichardening, thermal/static recovery, isotropic and anisotropic, etc.). Theentire procedure is automated through the integrated software COMPARE(an acronym for COnstitutive Material PARameter Estimator) to enable thedetermination of an `optimum' set of material parameters by minimizingthe errors between the experimental test data and the predictedresponse. The key ingredients of COMPARE are: (i) primal analysisutilizing the unconditionally-stable, fully implicit, integration schemefor the models' underlying flow and evolutionary rate equations; (ii) sensitivity analysis utilizing a direct-differentiation approach (i.e.,explicit, `exact' expressions are derived); (iii) a gradient-basedoptimization technique of an error/cost function; and (iv) graphicaluser interface. The estimation of the material parameters is cast as aminimum-error, weighted-multi-objective, nonlinear optimization problemwith constraints. Comparison between the sensitivities obtained by theproposed direct scheme and those produced by conventional finitedifference techniques is presented to assess accuracy. Detailedderivations are given, together with the results generated by applyingthe developed algorithms to a comprehensive set of test matrices. Theseinclude constant strain-rate tension, creep, and relaxation tests, forboth isotropic as well as anisotropic behaviors.     

A Multiscale Model for the Effective Thermal Conductivity Tensor of a Stratified Composite Material

Thermal modeling of composites has three essential objectives: (i) comprehension of their thermal behavior; (ii) composite scaling in order to satisfy specific requirements; and (iii) optimal analysis of experimental results from thermal characterization. For a complete study of the material, each of these three points must be taken into account at the fiber scale ( 10m), the yarn scale ( 1 mm), and the composite scale ( 10 cm). This work presents multi-scale modeling of the effective thermal conductivity tensor of a stratified composite material made from carbon fibers, phenolic resin, and carbon loads. The longitudinal and transverse thermal conductivities of the yarn are computed from optical microscopic imaging of the material. The isotropic thermal conductivity of the loaded matrix is computed by the Bruggeman model. Then, the thermal conductivity tensor is determined by a finite element method taking into account the morphology of the fabric. Computed values are close to experimental values measured by classical methods. Finally, analytical relations are proposed to obtain an efficient model which can be used in a multiphenomenon simulation of the composite structure.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

Analysis of the Dependence of the Range of the Edge Effect in a Laminated Composite with Transversely Isotropic Filler on the Mechanical Characteristics

We study the dependence of the range of the edge effect in a two-component composite with regular structure on the Young moduli and Poisson ratios of the components. The layers filled with a filler and binder are modeled by transversely isotropic and isotropic linearly elastic bodies, respectively. The composite is subjected to the action of a piecewise constant loading applied to the layer of filler. To find approximate solutions of problems in the theory of the edge effect, we use the method of grids based on the concept of basic schemes. We perform an analysis of the accumulated results.     

Frequency Methods Applied to the Characterization of the Thermophysical Properties of a Granular Material with a Cylindrical Probe

In many fields, such as in the agri-food industry or in the building industry, it is important to be able to monitor the thermophysical properties of granular materials. Regular thermal probes allow for the determination of one or several thermophysical factors. The success of the method used depends in part on the nature of the signal sent, on the type of physical model applied and eventually on the type of probe used and its implantation in the material. Although efficacious for most applications, regular thermal probes do present some limitations. It is the case, for example, when one has to know precisely the thermal contact resistance or the nature of the signal sent. In this article is presented a characterization method based on thermal impedance formalism. This method allows for the determination of the thermal conductivity, the thermal diffusivity, and the contact thermal resistance in one single test. The application of this method requires the use of a specific probe developed to enable measurement of heat flux and temperature at the interface of the probe and the studied material. Its practical application is presented for dry sand.     

Investigation of Flow in the Vicinity of Porous Material on a Cylindrical Body Subjected to Flow

The results are given of an experimental investigation of the distribution of velocity components in a flow of air in the vicinity of a hemispherical permeable blunting of a cylindrical body under conditions of low injection intensity. A numerical simulation of the flow structure is performed for the parameters corresponding to those used in the experiments. Comparison of the results of physical and numerical simulation revealed a number of special features of flow in the boundary layer on a curved surface under conditions of its gasdynamic conjugation with the inner cavity.     

Propagation of a Thermoelastic Wave in a Half-Space of a Homogeneous Isotropic Material Subjected to the Effect of Rotation and Initial Stress

The propagation of thermoelastic waves in a homogeneous, isotropic elastic semi-infinite space is subjected to rotation and initial stress, which is at temperature T₀ -initially, and whose boundary surface is subjected to heat source and load moving with finite velocity. Temperature and stress distribution occurring due to heating or cooling and have been determined using certain boundary conditions. Numerical results have been given and illustrated graphically in each case considered. Comparison is made with the results predicted by the theory of thermoelasticity in the absence of rotation and initial stress. The results indicate that the effect of the rotation and initial stress is very pronounced.     

标准物质稳定性不确定度的评估

基于ISO导则35,说明批量研制或制备的标准物质稳定性的不确定度评估方法.标准物质特性量值的变化在没有可知的物理或化学的模型来描述时,可采用趋势分析法和方差分析法来评估不稳定性引入的不确定度分量.用趋势分析法判断标准物质是否稳定,用方差分析法计算不稳定性引入的不确定度,2种方法结合起来使用可使标准物质稳定性不确定度的评估更加科学、合理.     

Stability of Cylindrical Shells with Regard for Dispersed Cracking in the Material

The problems of bifurcation stability of cylindrical shells are stated and solved with regard for the damage to a material in the subcritical stressed state. The appearance of defects in the material is explained by the inhomogeneity of its microstrength. The defects are simulated by a system of plane elliptic and circular cracks statistically uniformly and isotropically distributed over the volume of a shell. The mathematical statement of the problem is performed within the framework of the Kirchhoff–Love hypotheses by using the concept of continued loading. The solution of the problem is constructed for the case of uniform compression of the shell.     

Resistivity Tensor in the Normal State of BSCCO Single Crystals as a Function of Doping

We present measurements of the resistivity tensor of Bi₂Sr₂CaCu₂O₈+ single crystals with different oxygen concentrations. Sample doping varies from underdoped to slightly overdoped. Measurements are performed through multiterminal technique, which allows for a simultaneous determination of both in-plane and out-of-plane components of the resistivity tensor. Data are analyzed in terms of a model that assumes two different mechanisms for the out-of-plane conduction, markedly thermal activation and incoherent tunneling. Within this model we are able to describe data of normal state resistivity for all samples with different doping levels. We also analyze data from the literature. In all cases, the proposed model describes very well the data in the normal state.     

A Meshless Local Petrov-Galerkin Method for the Analysis of Cracks in the Isotropic Functionally Graded Material

A meshless local Petrov-Galerkin method (MLPG) [[Atluri and Zhu (1998)] for the analysis of cracks in isotropic functionally graded materials is presented. The meshless method uses the moving least squares (MLS) to approximate the field unknowns. The shape function has not the Kronecker Delta properties for the trial-function-interpolation, and a direct interpolation method is adopted to impose essential boundary conditions. The MLPG method does not involve any domain and singular integrals to generate the global effective stiffness matrix if body force is ignored; it only involves a regular boundary integral. The material properties are smooth functions of spatial coordinates and two interaction integrals [Rao and Rahman (2003a,b)] are used for the fracture analysis. Two numerical examples including both mode-I and mixed-mode problems are presented to calculated the stress intensity factors (SIFs) by the proposed method. Example problems in functionally graded materials are presented and compared with available reference solutions. A good agreement obtained show that the proposed method possesses no numerical difficulties.     

Analytical Solution to the Plane Bending Task of the Multilayer Beam with a Circular Axis under Normal Uniform Loading

Strength of Materials - Circular bars are widespread elements in building and mechanical engineering. They allow one to enhance the strength of the multilayer composite materials along with their...     

Plane Elastic Problem of a Crack Normal to and Terminating at Bimaterial Interface of Isotropic and Orthotropic Half Plates

In this paper, the displacement and stress fields for a crack normal to and terminating at a bimaterial interface of isotropic and orthotropic half planes are studied as a plane problem. The eigenequation, by which the order of stress singularity is determined, is given in an explicit form. A discriminant function is presented to judge whether the stress singularity at the crack tip is greater than -1/2 or not. An explicit closed form expression is derived for the displacement and stress distribution near the crack tip.     

Verification of the Hypothesis of Compliance of the Errors of the Results of Analyses of Oil Products to the Normal Distribution Law for a Random Variable

Measurement Techniques - We test the normality of the distribution of united samples of errors of the results of analysis of various types and brands of oil products obtained in the course of...     

Approximate equation for the mass or heat flux to droplets of a concentrated cloud

An approximate equation is derived for the Sherwood number, which is a measure of the convective diffusion to a liquid droplet under conditions of constrained flow.