Prediction of ionic structure in hydrocarbon flames

The objective of this research is to model the appearance and behavior of combustion-generated ions in hydrocarbon flames. An understanding of ionic phenomena is important to the development of advanced combustion technology including electrical control of flame structure and suppression of soot formation. Computer models have been developed to evaluate the formation and behavior of ions in acetylene flames;The results of computations are compared to experimental data of other researchers. Several important qualitative features have been successfully modeled. Peak ion concentrations of 10(\u279) to 10(\u2711) cm(\u27-3) are consistent with experimental measurements. The ratio of large ions to small ions increases sharply as the flame is made richer. The build-up and decay rates of ions observed experimentally are predicted by the model

Elastoplastic deformations of rotating parabolic solid disks using Tresca's yield criterion

Analytical solutions for the stress distribution in rotating parabolic solid disks are obtained. The analysis is based on Tresca's yield criterion, its associated flow rule and linear strain hardening. It is shown that, the deformation behavior of the convex parabolic disk is similar to that of the uniform thickness disk, but in the case of concave parabolic solid disk, it is different. In the latter, the plastic core consists of three different plastic regions with different mathematical forms of the yield criteria. Accordingly, three different stages of elastic-plastic deformation occur. All these stages of elastic-plastic deformation are studied in detail. It is also shown mathematically that in the limiting case the parabolic disk solution reduces to the solution of rotating uniform thickness solid disk

On the linearly hardening rotating solid shaft

Analytical solutions are obtained for elastic-plastic deformations of a linearly hardening rotating solid shaft with fixed ends and with free ends. All stages of elastic-plastic deformations are studied using Tresca's yield condition and the flow rule associated with it. Expressions for the stresses, displacement and plastic strains for a perfectly plastic shaft can be deduced from the expressions of linearly hardening shaft by letting the hardening parameter vanish. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved

Thermally induced deformations of composite tubes subjected to a nonuniform heat source

Analytical solutions are obtained for thermally induced axisymmetric elastic and elastic-plastic deformations in nonuniform heat-generating composite tubes with fixed ends. Thermoelastic solutions are obtained using four different boundary conditions: (i) free, (ii) radially constrained and free, (iii) free and pressurized, (iv) free and radially constrained. Elastic-plastic solutions are obtained for a composite tube having free inner and radially constrained outer boundaries using Tresca's yield condition and its associated flow rule. The first two stages of elastic-plastic deformations are studied considering nonlinearly hardening, linearly hardening, and perfectly plastic material behavior. The theory developed is illustrated in several numerical examples

Stress distributions in elastic-plastic rotating disks with elliptical thickness profiles using Tresca and von Mises criteria

Analytical and numerical solutions for the elastic-plastic stress distribution in rotating variable thickness solid and annular disks are obtained under plane stress assumption. The thickness of the disk is assumed to vary radially in elliptic form which represents a wide range of continuously variable nonlinear cross-sectional profiles. Tresca's yield criterion and its associated flow rule are used to obtain analytical solutions for a linear hardening material. A computational model is developed to obtain solutions using the von Mises yield criterion, deformation theory of plasticity and a Swift-type hardening law. Both linear and nonlinear hardening materials are considered in solutions obtained by using von Mises criterion. The stresses, displacement and plastic strains are calculated for solid and annular disks rotating at different speeds and the results are presented in graphical forms

A Class of Nonisothermal Variable Thickness Rotating Disk Problems Solved by Hypergeometric Functions

Exact solutions for nonisothermal variable thickness rotating disks represented by different thickness profiles are obtained under plane stress assumption. The solutions are based on Tresca's yield criterion, its associated flow rule and linear strain hardening material behavior. Five different plastic regimes governed by different mathematical forms of the yield criterion are considered for each thickness profile. A displacement formulation is used and the resulting differential equations for the elastic and plastic regions are solved in terms of hypergeometric functions by the introduction of appropriate transformations

Von mises yield criterion and nonlinearly hardening variable thickness rotating annular disks with rigid inclusion

A computational model is developed to investigate inelastic deformations of variable thickness rotating annular disks mounted on rigid shafts. The von Mises yield condition and its flow rule are combined with Swift's hardening law to simulate nonlinear hardening material behavior. An efficient numerical solution procedure is designed and used throughout to handle the nonlinearities associated with the von Mises yield condition and the boundary condition at the shaft-annular disk interface. The results of the computations are verified by comparison with an analytical solution employing Tresca's criterion available in the literature. Inelastic stresses and deformations are calculated for rotating variable thickness disks described by two different commonly used disk profile functions i.e. power and exponential forms. Plastic limit angular velocities for these disks are calculated for different values of the geometric and hardening parameters. These critical angular velocities are found to increase as the edge thickness of the disk reduces. Lower plastic limit angular velocities are obtained for disks made of nonlinearly hardening materials

Stresses in FGM pressure tubes under non-uniform temperature distribution

The effects of material nonhomogeneity and nonisothermal conditions on the stress response of pressurized tubes are assessed by virtue of a computational model. The modulus of elasticity, the Poisson's ratio, the yield strength, and the coefficient of thermal expansion, are assumed to vary nonlinearly in the tube. A logarithmic temperature distribution within the tube is proposed. Under these conditions, it is shown that the stress states and the magnitudes of response variables are affected significantly by both the material nonhomogeneity and the existence of the radial temperature gradient

Tresca's yield criterion and linearly hardening rotating solid disks having hyperbolic profiles

An analytical solution for the stress distribution in rotating hyperbolic solid disk is obtained under plane stress assumption. The analysis is based on Tresca's yield criterion, its associated flow rule and linear strain hardening material behavior. It is shown that the deformation behavior of the hyperbolic solid disk is different from that of the constant thickness disk. The plastic core consists of three different plastic regions with different mathematical forms of the yield criterion. Accordingly, three different stages of elastic-plastic deformation can be distinguished. The lower and upper bounds of the limit angular velocities for each stage are determined. It is also shown mathematically that in the limiting case the hyperbolic disk solution reduces to the solution of rotating uniform thickness solid disk