动态扩展裂纹的热-弹塑性耦合分析

以弹塑性扩展裂纹的裂尖参数为研究对象 ,对快速扩展的裂纹问题进行了细致的分析。首先建立了经验的应变率以及热 -弹塑性耦合的材料本构关系 ,完善了增量路径无关积分参数 T*的数值计算。通过与 J积分的比较 ,给出了两种积分参数在不同扩展速度、是否考虑热和应变率影响等情况下的变化规律 ,说明了T*积分用于快速扩展裂纹的合理性和优越性。在裂尖场的讨论中 ,重点分析了裂尖应力、应变、应力三轴度和塑性区的演化发展过程 ,发现了快速扩展裂纹塑性区发展非单调的有趣现象 。

Elasticity under pressure and thermal property of Mg2La from first-principles calculations

The elastic properties, thermodynamic and electronic structures of Mg_2La were investigated by using first-principles. The calculated results show that pressure affects the elastic constants of C_(11) more than that of C_(12) and C_(44). Specifically, higher pressure leads to greater bulk modulus(B), shear modulus(G), and elastic modulus(E). We predict B/G and anisotropy factor A based on the calculated elastic constants. The Debye temperature also increases with increasing pressure. Based on the quasi-harmonic Debye model, we examined the thermodynamic properties. These properties include the normalized volume(V/V_0), bulk modulus(B), heat capacity(C_v), thermal expansion coefficient(α), and Debye temperature(■). Finally, the electronic structures associated with the density of states(DOS) and Mulliken population are analyzed.

NONLINEAR MODEL OF THERMOVISCOELASTICITY UNDER VARYING TEMPERATURE AND ITS APPLICATIONS IN DESIGN OF THE MOLDS OF CRT GLASS BULB

A non linear constitutive model is suggested for the thermoviscoelastic materials that undergo varying temperature histories.The description of the model is based on the concepts similar to those in a linear thermoviscoelastic model,such as relaxation surface at constant temperatures,relaxation curve along a varying temperature history and equivalent relaxation curve in the terminal temperature plane.The non linear model has been applied to the simulation of deformation of the molds of CRT glass bulb.The numerical results show better agreements with the measured data of the molds than the ones based on the linear model.

Influence of thermal contact resistance on dynamic response of bilayered saturated porous strata

Porous materials can be found in a variety of geophysical and engineering applications.The existence of thermal contact resistance at the interface between bilayered saturated porous strata would result in a significant temperature difference at the interface.An attempt is made to study the thermo-hydro-mechanical coupling dynamic response of bilayered saturated porous strata with thermal contact resistance and elastic wave impedance.The corresponding analytical solutions for the dynamic response of bilayered saturated porous strata under a harmonic thermal load are derived by the operator decomposition method,and their rationality is verified by comparing them with existing solutions.The influences of thermal contact resistance,thermal conductivity ratio,and porosity ratio on the dynamic response of bilayered saturated porous strata are systematically investigated.Outcomes disclose that with the increase of thermal contact resistance,the displacement,pore water pressure and stress decrease gradually,and the temperature jump at the interface between two saturated porous strata increases.

A comprehensive comparison on vibration and heat transfer of two elastic heat transfer tube bundles

Elastic heat transfer tube bundles are widely used in the field of flow-induced vibration heat transfer enhancement. Two types of mainly used tube bundles, the planar elastic tube bundle and the conical spiral tube bundle were comprehensively compared in the condition of the same shell side diameter. The natural mode characteristics, the effect of fluid-structure interaction, the stress distribution, the comprehensive heat transfer performance and the secondary fluid flow of the two elastic tube bundles were all concluded and compared. The results show that the natural frequency and the critical velocity of vibration buckling of the planar elastic tube bundle are larger than those of the conical spiral tube bundle, while the stress distribution and the comprehensive heat transfer performance of the conical spiral tube bundle are relatively better.

Thermoelastoplastic Deformation Analysis of Electromechanical Equipments under Electrocaloric Shock

A coupled thermomechanical model is presented to investigate the thermoelastoplastic deformation mechanism of electromechanical equipments under the condition of electrocaloric shock. In the coupling model, differentiating from the previous analyzing viewpoint that looked upon deformation work as additional heat source, temperature-field equation is established by considering the weakening role of deformation work on the intensity of internal heat source; in the process of setting up displacement-field equation, G-derivative of nonlinear functional is introduced into the traditional theory of elastoplastic finite deformation to simplify the expression of structural stiffness; stress-field equation is constructed by using the least square method to improve the stress solution obtained by constitutive equation. The presented model is converted into finite element program to simulate deforming process of 3-D structures with temperature-dependent material properties. As an example, thermal deformation analysis of Shanghai metro cars’ brake resistor is performed and compared with experimental results for illustrating the validity of the presented model.

MHD three dimensional flow of viscoelastic fluid with thermal radiation and variable thermal conductivity

The objective of the present work is to model the magnetohydrodynamic(MHD) three dimensional flow of viscoelastic fluid passing a stretching surface. Heat transfer analysis is carried out in the presence of variable thermal conductivity and thermal radiation. Arising nonlinear analysis for velocity and temperature is computed. Discussion to importantly involved parameters through plots is presented. Comparison between present and previous limiting solutions is shown. Numerical values of local Nusselt number are computed and analyzed. It can be observed that the effects of viscoelastic parameter and Hartman number on the temperature profile are similar in a qualitative way. The variations in temperature are more pronounced for viscoelastic parameter K in comparison to the Hartman number M. The parameters N and ε give rise to the temperature. It is interesting to note that values of local Nusselt number are smaller for the larger values of ε.

A new interpretation of internal-variable theory in finite thermo-viscoelasticity

Based on the non-equilibrium thermodynamics,an internal-variable theory in thermo-viscoelasticity at finite deformation was proposed by Huang in 1999.In this theory,a modified stretch of the molecular chain was introduced,and hence the molecular network model in rubber elasticity was extended to take into account the viscous and thermal effects of the material.The viscous dissipation of the material can then be described by means of these internal variables,which appear in the expression of the modified stretch.In order to give a clearer explanation on the physical implication of the internal variables,a connection between the internal-variable theory and theoretical formulation based on the multiplicative decomposition of the deformation gradient in existing literature is presented in this paper,which allows the above internal-variable theory to be more systematic.

Thermoelastic coupling problems caused by thermal contact resistance:A discontinuous Galerkin finite element approach

A discontinuous Galerkin (DG) finite element method is presented to solve the thermoelastic coupling problems caused by temperature and pressure dependent thermal contact resistance (TCR).The whole analysis is made up of two parts,thermal and mechanical analysis.In thermal analysis,the DG method is employed to simulate the temperature jump phenomenon,which satisfies the imperfect thermal contact condition in a straightforward manner.In mechanical analysis,the impenetrability condition is fulfilled through a DG approach with penalty functions.The Picard iteration procedure with a relaxation technique is also adopted to accelerate the rate of convergence and avoid numerical instability.Numerical examples show that the present method is an attractive approach for solving thermoelastic coupling problems caused by TCR.The methodology can also be expanded to solve problems with friction finite deformation contact,node-to-segment contact and node-to-surface contact,etc.in a straightforward manner.

On Plane Stress State and Stress Free Deformation of Thick Plate with FGM Interface under Thermal Loading

This paper demonstrates the plane stress state and the stress free thermo-elastic deformation of FGM thick plate under thermal loading.First,the Sneddon-Lockett theorem on the plane stress state in an isotropic infinite thick plate is generalized for a case of FGM problem in which all thermo-mechanical properties are optional functions of depth co-ordinate.The proof is based on application of the Iljushin thermo-elastic potential to displacement type system of equations that reduces it to the plane stress state problem.Then an existence of the purely thermal deformation is proved in two ways:first,it is shown that the unique solution fulfils conditions of simultaneous constant temperature and linear gradation of thermal expansion coefficient,second,proof is based directly on stress type system of equations which straightforwardly reduces to compatibility equations for purely thermal deformation if only stress field is homogeneous in domain and at boundary.Finally,couple examples of application to an engineering problem are presented.

Integral Transform Methods for Inverse Problem of Heat Conduction with Known Boundary of a Thin Rectangular Object and its Stresses

The three-dimensional inverse transient thermoelastic problem for a thin rectangular object is considered within the context of the theory of generalized thermoelasticity. The upper surface of the rectangular object occupying the space D： -a〈xSa; -b〈_y〈b; 0〈z〈h; with the known boundary conditions. Laplace and Finite Marchi-Fasulo transform techniques are used to determine the unknown temperature, temperature distribution, displacement and thermal stresses on upper plane surface of a thin rectangular object. The distributions of the considered physical variables are obtained and represented graphically.