Search

A numerical-analytic structural model of thermoelastoplastic deformation of a composite material cross-reinforced with fibers in arbitrary directions is developed on the basis of the time-steps algorithm. The materials of constituents of the composition are isotropic; their plastic deformation is described by the theory of flow with isotropic hardening taking into account the dependence of the loading function on temperature. Conditions determining thermoelastic deformation, unloading, neutral and active loading of thermosensitive constituents of the composition are obtained. The coupled problems of the thermophysical and mechanical behavior of reinforced materials are considered. Structural relationships that are necessary for solving the thermophysical component of the investigated problem are presented. The developed structural model is focused on the use of explicit numerical integration schemes for both elastoplastic and thermophysical problems. [ABSTRACT FROM AUTHOR]

The article presents models of superelastic hardening of materials with unstable phase structure at a constant temperature. The kinetic equation of the process of formation and growth of spherical nuclei of a new phase is formulated depending on the level of development of inelastic structural deformations, according to which the new phase first represents separate inclusions from embryos, developing it forms the structures of the matrix mixture in the form of interpenetrating skeletons, and finally the new phase is transformed in a matrix with separate inclusions from the material of the remains of the old phase. The influence of structural deformations on the features of phase transformations and nonlinear hardening of inhomogeneous unstable materials with different degree of connectivity of the constituent phases is studied. Various variants of the microstructure material formed in the conditions of the phase transition in the form of separate inclusions and in the form of interpenetrating components are considered. New macroscopic determining relationships for unstable microinhomogeneous materials are established and their effective elastic moduli are calculated. Macroscopic conditions of direct and inverse phase transitions are obtained, their effective limits and hardening coefficients are calculated. It is shown that the values of the macroscopic elasticity moduli of the obtained models lie inside the fork of the lower and upper Hashin-Shtrikman boundaries. Numerical analysis of the developed models has shown good agreement with known experimental data.

This research tries to investigate the relationships among factors of satisfaction, image, trust, effective relations, and loyalty. The statistical population of this research consists of members of the Iran Air’s Sky Gift Club (In three levels of Gold, Silver and Blue). As for the sampling technique, random sampling is used; and questionnaire is employed as data gathering tool. For the reliability testing we get use of split-half technique. Additionally, tests of Chi-square, Friedman and Spearman's correlation coefficient are conducted for examining the research questions and obtaining the results. Findings demonstrate that factors of satisfaction, image, trust, and effective relations, have influence on passengers’ loyalty in every one of the three levels, although differing in priority of impacts. According to the findings, for Golden Passengers the most effective factor on the loyalty is trust, while the least effective belongs to image. In the Silver level, effective relations have the most and image has the least influence on loyalty. In the Blue level, satisfaction and effective relations are of the most and the least influences respectively.

Abstract: Effective constitutive relations for waves in composites with random microstructure were proposed by as relations between ensemble averages of stress and momentum, and “effective” strain and velocity which were related to a weighted ensemble average of displacement, and results of an example one-dimensional calculation were presented, explicitly demonstrating the possibility of coupling between mean stress and effective velocity, and mean momentum density and effective strain, even in the long-wavelength (or homogenization) limit. Relations of this type have recently been recognized to be inevitably non-unique, and a quite general prescription for defining unique relations has been advanced (). The present work compares and contrasts the effective relations obtained by either formulation, for the example considered in 2009. The work of 2009 is generalized to the extent that the constituent materials are taken to have some dissipation. It emerges explicitly that an “effective elastic constant” obtained by the method of 2009 can display an apparent energy gain rather than loss. This is not the only term that contributes, however, and it is shown that the effective material remains dissipative, as it should. It is also confirmed, both theoretically and in the computation, that either formulation leads to exactly the same mean stress and momentum density, and to the same dissipation. [Copyright &y& Elsevier]

Abstract: Implications of a recent general formulation for the effective dynamic response of a composite, in which “effective displacement” is defined as a weighted average, which could, for instance, be an average over the matrix material, are developed. A general formula is already known [J.R. Willis, Effective constitutive relations for waves in composites and metamaterials, Proc. R. Soc. A 467 (2011) 1865–1879], but it is expressed in terms of the Greenʼs function of the actual composite. A corresponding formula, expressed relative to a comparison medium, is developed here. The property of self-adjointness of the problem for the actual medium is transmitted to the corresponding problem for the “effective medium”. This permits, in the case of self-adjointness, variational characterizations of the effective response, both directly and in a formulation of “Hashin–Shtrikman” type relative to a comparison medium. The exposition is for waves in a viscoelastic composite but it applies equally to other physical examples, including electromagnetic waves. [Copyright &y& Elsevier]

Definitions of 'effective fields' for a randomly inhomogeneous material are offered, which guarantee automatic satisfaction of the equations of motion. The important case of a medium with periodic microstructure is included. In this special case, the definitions are completely explicit and can be applied without reference to random media. The presentation is mostly expressed in terms of electromagnetic waves. The reasoning is applicable also to other types of waves and its realization for elastodynamics is briefly outlined towards the end. Some of the effective fields are defined directly as ensemble averages, ensuring the exact satisfaction of the equations of motion, but the effective 'kinematic' fields to which they are related are defined more generally, as weighted averages. The main result of this work is an explicit formula for the tensor of effective properties. The important issue of uniqueness (or not) of the effective properties is explained and resolved. Self-adjointness of the original problem is not assumed. An attractive feature of the formulation is that self-adjointness at the local level implies self-adjointness at the level of the 'effective medium'. [ABSTRACT FROM AUTHOR]