A wavelet-based methodology for monitoring thermoelastic structures

A wavelet-based methodology for detecting critical events in displacement and temperature histories, obtained by monitoring in-situ thermoelastic structures, is proposed. It is based on the wavelet analysis of thermoelastic potentials furnishing also the possibility to detect separately cases in which sudden jumps occur in the displacement history from those in which they occur on temperature history.     

On the propagation waves in the theory of thermoelasticity with microtemperatures

The present paper studies the propagation of plane time harmonic waves in an infinite space filled by a thermoelastic material with microtemperatures. It is found that there are seven basic waves traveling with distinct speeds: (a) two transverse elastic waves uncoupled, undamped in time and traveling independently with the speed that is unaffected by the thermal effects; (b) two transverse thermal standing waves decaying exponentially to zero when time tends to infinity and they are unaffected by the elastic deformations; (c) three dilatational waves that are coupled due to the presence of thermal properties of the material. The set of dilatational waves consists of a quasi-elastic longitudinal wave and two quasi-thermal standing waves. The two transverse elastic waves are not subjected to the dispersion, while the other two transverse thermal standing waves and the dilatational waves present the dispersive character. Explicit expressions for all these seven waves are presented. The Rayleigh surface wave propagation problem is addressed and the secular equation is obtained in an explicit form. Numerical computations are performed for a specific model, and the results obtained are depicted graphically.     

A Phragmèn-Lindelöf principle for the thermoelastic cylinder of variable cross-section

We consider a non-prismatic cylinder consisting of an anisotropic, compressible, inhomogeneous thermoelastic material, subject to either null tractions or null displacements on the lateral boundary and loaded by a self-equilibrated force system at one end. We show that the mean square cross-sectional measures of the temperature and the coupled displacement—temperature either grow faster than an exponentially increasing function of axial distance or decrease faster than a decaying exponential function of axial distance. We thus establish a Phragmèn-Lindelöf principle for the thermoelastic cylinder of variable cross-section.

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Sommario Viene considerato un cilindro non-prismatico costituito da un materiale termoelastico, anisotropo, comprimibile ed omogeneo. Il cilindro é soggetto a zero trazioni o zero dislocamenti sul limite laterale ed é caricato su uno dei termini con un sistema autoequilibrilata delle forze. Mostriamo che il valore medio quadratico della temperatura e dell'accoppiata della temperatura ed il dislocamento cresce più veloce che una funzione esponenziale crescente della distanza assiale o diminuisce più veloce che una funzione esponenziale declinante della distanza assiale. Viene stabilito un principio di Phragmèn-Lindelöf per il cilindro termoelastico di sezione trasversale variabile.

     

Two-dimensional thermoelastic analysis of a functionally graded cylindrical panel due to nonuniform heat supply

This paper is concerned with the theoretical treatment of the steady-state thermoelastic problem of a functionally graded cylindrical panel due to nonuniform heat supply in the circumferential direction. The thermal and thermoelastic constants of the cylindrical panel are expressed as power functions of the radial coordinate. We obtain the exact solution for the two-dimensional temperature change in a steady state, and thermal stresses of a simple supported cylindrical panel under the state of plane strain. Some numerical results are shown in figures and tables. Furthermore, the influence of the nonhomogeneity of the material, the radius ratio and the span angle upon the temperature change, displacements and stresses is investigated.     

A uniform stability result for thermoelasticity of type III with boundary distributed delay

In this paper we consider a thermoelastic system of type III with boundary distributed delay. Under suitable assumption on the weight of the delay, we prove, using the energy method, that the damping effect through heat conduction given by Green and Naghdi's theory is still strong enough to uniformly stabilize the system even in the presence of time delay.     

高压下MgO的热弹性研究

利用第一原理平面波赝势方法和广义梯度近似研究了广泛温度和压强范围内MgO的热弹性特性．MgO从低压NaCl到高压CsCl结构的相变压强为397 GPa，表明它在地球内部不会发生相变．在压强上升到150 GPa时，MgO的绝热弹性模量跟0 GPa时的实验值和其他赝势在高压下的计算结果基本一致．从0 GPa上升到20 GPa时，MgO的各向异性逐渐减小；在20?150 GPa时绝对值逐渐增大．MgO明显地违背了Cauchy条件，反应出非中心多体力是重要的．另外，MgO的热力学参量与实验也符合的很好．     

Thermoelasticity and stress relaxation behavior of polychloroprene/organoclay nanocomposites

Polychloroprene/organoclay nanocomposites (ENC) were characterized by X-ray scattering, DSC and stretching calorimetry techniques.The infinite cluster of highly anisometric organoclay particles was likely to set on at filler volume fraction as low as ? ? 0.04. Quantitative analysis of thermoelastic behavior over the entire range of relative elongations provided additional support for the concept of strain-dependent strain amplification factor as the major parameter controlling the thermomechanical properties of the ENC. Low values of the fitting parameter C in the modified equation for the total heats of stretching were regarded as evidence for the reduced exothermal effects of external friction between organoclay nanoparticles coated with the boundary interphase. Stress relaxation behavior of the ENC was qualitatively consistent with the original assumption that after initial stretching to the highest elongation (λ_lim) the pre-existing infinite clusters of filler particles were broken into isolated clusters which remained structurally similar, whatever the subsequent stretching to λ_f < λ_lim.     

Existence for the thermoelastic thermistor problem

We study a new model for the thermistor problem that consists of a system of dynamic thermoelasticity equations of displacement and a stationary charge conservation equation of electrical current. The heat source generated by Joule heating is quadratic in the gradient of the electrical potential. This system is nonlinear and degenerate since the electrical conductivity is assumed to be temperature dependent and vanishes at large temperatures. We establish the existence of a very weak solution, the so-called “capacity solution” for the model. The proof is based on regularization and time retarding.     

Thermoelasticity of bodies with microstructure and microtemperatures

This paper is concerned with a linear theory of thermodynamics for elastic materials with microstructure, whose microelements possess microtemperatures. It is shown that there exists the coupling of microrotation vector field with the microtemperatures even for isotropic bodies. Uniqueness and continuous dependence results are presented. The theory is used to establish the solution corresponding to a concentrated heat source acting in an unbounded continuum.     

Determining stress intensity factors in orthotropic composites from far-field measured temperatures

We demonstrate the ability to determine stress intensity factors in orthotropic materials directly from measured temperatures away from the crack and using far-field expressions for the stresses. This is advantageous, recognizing that recorded thermoelastic data can be very unreliable near the tip of a crack. In addition to singular terms that govern in the immediate vicinity of the crack tip, the present series expressions for the stresses contain higher-order finite terms. Little measured input information is needed and data acquisition positions can be selected largely at the user's discretion.