Showing papers on "Thermoelastic damping published in 2013"

Thermal Conductivity of High-Modulus Polymer Fibers

Abstract: Polymers have many desirable properties for engineering systems–e.g., low mass density, chemical stability, and high strength-to-mass ratio–but applications of polymers in situations where heat transfer is critical are often limited by low thermal conductivity. Here, we leverage the enormous research and development efforts that have been invested in the production of high-modulus polymer fibers to advance understanding of the mechanisms for thermal transport in this class of materials. Time-domain thermoreflectance (TDTR) enables direct measurements of the axial thermal conductivity of a single polymer fiber over a wide temperature range, 80 < T < 600 K. Relaxation of thermoelastic stress in the Al film transducer has to be taken into account in the analysis of the TDTR data when the laser spot size is small because the radial modulus of the fiber is small. This stress relaxation is controlled by the velocity of the zero-order symmetric Lamb mode of a thin Al plate. We find similarly high thermal conduct...

Multi-objective concurrent topology optimization of thermoelastic structures composed of homogeneous porous material

Abstract: The present paper studies multi-objective design of lightweight thermoelastic structure composed of homogeneous porous material. The concurrent optimization model is applied to design the topologies of light weight structures and of the material microstructure. The multi-objective optimization formulation attempts to find minimum structural compliance under only mechanical loads and minimum thermal expansion of the surfaces we are interested in under only thermo loads. The proposed optimization model is applied to a sandwich elliptically curved shell structure, an axisymmetric structure and a 3D structure. The advantage of the concurrent optimization model to single scale topology optimization model in improving the multi-objective performances of the thermoelastic structures is investigated. The influences of available material volume fraction and weighting coefficients are also discussed. Numerical examples demonstrate that the porous material is conducive to enhance the multi-objective performance of the thermoelastic structures in some cases, especially when lightweight structure is emphasized. An "optimal" material volume fraction is observed in some numerical examples.

Simulating liquids and solid-liquid interactions with lagrangian meshes

Abstract: This article describes a Lagrangian finite element method that simulates the behavior of liquids and solids in a unified framework. Local mesh improvement operations maintain a high-quality tetrahedral discretization even as the mesh is advected by fluid flow. We conserve volume and momentum, locally and globally, by assigning to each element an independent rest volume and adjusting it to correct for deviations during remeshing and collisions. Incompressibility is enforced with per-node pressure values, and extra degrees of freedom are selectively inserted to prevent pressure locking. Topological changes in the domain are explicitly treated with local mesh splitting and merging. Our method models surface tension with an implicit formulation based on surface energies computed on the boundary of the volume mesh.With this method we can model elastic, plastic, and liquid materials in a single mesh, with no need for explicit coupling. We also model heat diffusion and thermoelastic effects, which allow us to simulate phase changes. We demonstrate these capabilities in several fluid simulations at scales from millimeters to meters, including simulations of melting caused by external or thermoelastic heating.

Two-temperature generalized thermoelasticity under ramp-type heating by finite element method

Abstract: In this work, a general finite element model is proposed to analyze transient phenomena in thermoelastic half-space filled with an elastic material, which has constant elastic parameters. The governing equations are taken in the context of the two-temperature generalized thermoelasticity theory (Youssef in IMA J. Appl. Math. 71(3):383–390, 2006). A linear temperature ramping function is used to more realistically model thermal loading of the half-space surface. The medium is assumed initially quiescent. A finite element scheme is presented for the high accuracy numerical purpose. The numerical solutions of the non-dimensional governing partial differential equations of the problem have been shown graphically and some comparisons have been shown in figures to estimate the effect of the ramping parameter of heating and the parameter of two-temperature.

Appropriate viscous damping for nonlinear time-history analysis of base-isolated reinforced concrete buildings

Abstract: SUMMARY There is no consensus at the present time regarding an appropriate approach to model viscous damping in nonlinear time-history analysis of base-isolated buildings because of uncertainties associated with quantification of energy dissipation. Therefore, in this study, the effects of modeling viscous damping on the response of base-isolated reinforced concrete buildings subjected to earthquake ground motions are investigated. The test results of a reduced-scale three-story building previously tested on a shaking table are compared with three-dimensional finite element simulation results. The study is primarily focused on nonlinear direct-integration time-history analysis, where many different approaches of modeling viscous damping, developed within the framework of Rayleigh damping are considered. Nonlinear direct-integration time-history analysis results reveal that the damping ratio as well as the approach used to model damping has significant effects on the response, and quite importantly, a damping ratio of 1% is more appropriate in simulating the response than a damping ratio of 5%. It is shown that stiffness-proportional damping, where the coefficient multiplying the stiffness matrix is calculated from the frequency of the base-isolated building with the post-elastic stiffness of the isolation system, provides reasonable estimates of the peak response indicators, in addition to being able to capture the frequency content of the response very well. Furthermore, nonlinear modal time-history analyses using constant as well as frequency-dependent modal damping are also performed for comparison purposes. It was found that for nonlinear modal time-history analysis, frequency-dependent damping, where zero damping is assigned to the frequencies below the fundamental frequency of the superstructure for a fixed-base condition and 5% damping is assigned to all other frequencies, is more appropriate, than 5% constant damping. Copyright © 2013 John Wiley & Sons, Ltd.

Encyclopedia Of Thermal Stresses

Abstract: From the Contents: - Aero-Thermo-Elasticity, Aero-Magneto-Elasticity, Functionally Graded Plates, Shells and Beams.- Analytical (Computational) Thermomechanics.-Ceramics and Linear Fracture Mechanics.-Composites.-Contact Problems.-Coupled and Generalized Thermoelasticity.-Elastostatics and Thermoelastostatics.-Electro-Elastic Thermoelasticity and Smart Structures.-Electronics, Optoelectronics, Photonics, and MEMS (MOEMS) Packaging Engineering.-Fracture.-Heat Conduction-Direct, Inverse and Optimization.-Heat Treatment, Welding, and Shape Memory.-Linear and Nonlinear Viscoelasticity and Viscoplasticity.-Mathematical Preliminaries and Methods.-Methods of Complex Variables.-Nanotechnology, Special Methods in Thermal Stresses.-Plates.-Qualitive Properties of Thermoelastic Solutions.-Shells.-Simulation and Modeling-Thermal Stresses.-Stability.-Thermal Stress Resistance, Experimental Methods.-Thermal Stresses-Basic Problems.-Thermal Stresses Induced by Laser Heating.-Thermo-Inelasticity and Damage.-Thermodynamics of Thermodeformable Solids.-Thermoelastodynamics.-Transient Thermoelastic Waves and Dynamic Problems.-

On the three-phase-lag linear micropolar thermoelasticity theory

Abstract: The constitutive laws for the three-phase-lag micropolar thermoelasticity theory are given. The uniqueness and reciprocal theorems are proved and a variational principle is established for a linear micropolar anisotropic and inhomogeneous thermoelastic solid. A continuous dependence result is given for isotropic solid.

Effect Of Distinct Conductive And Thermodynamic Temperatures On The Reflection Of Plane Waves In Micropolar Elastic Half-Space

Abstract: The present investigation is concerned with wave propagation in micropolar thermoelastic solid half space with distinct conductive and thermodynamic temperatures. Reflection of plane waves incident obliquely at the free surface of micropolar generalized thermoelastic solid half space with two temperature is investigated. Amplitude ratios various reflected waves are obtained in closed form and it is found that these are function of angle of incidence, frequency and are affected by the micropolar thermoelastic properties of the medium. Effect of two temperatures is shown on these amplitude ratios for a specific model. Results of some earlier workers have also been deduced from the present investigation as a special case.

Wave turbulence in vibrating plates: The effect of damping

Abstract: The effect of damping in the wave turbulence regime for thin vibrating plates is studied. An experimental method, allowing measurements of dissipation in the system at all scales, is first introduced. Practical experimental devices for increasing the dissipation are used. The main observable consequence of increasing the damping is a significant modification in the slope of the power spectral density, so that the observed power laws are not in a pure inertial regime. However, the system still displays a turbulent behavior with a cut-off frequency that is determined by the injected power which does not depend on damping. By using the measured damping power-law in numerical simulations, similar conclusions are drawn out.

Modeling a Microstretch Thermoelastic Body with Two Temperatures

Abstract: We consider a theory of thermoelasticity constructed by taking into account the heat conduction in deformable bodies which depends on two temperatures. The first one is the conductive temperature, the second is the thermodynamic temperature, and the difference between them is proportional to the heat supply.

Asymptotic homogenization of periodic thermo-magneto-electro-elastic heterogeneous media

Abstract: The asymptotic homogenization method is applied to a family of boundary value problems for linear thermo-magneto-electro-elastic (TMEE) heterogeneous media with periodic and rapidly oscillating coefficients. Using a matrix notation, the procedure for constructing the formal asymptotic solution is described. Two ways to validate the asymptotic analysis are explained. The main differences/similarities with respect to the asymptotic homogenization models reported in recent papers are remarked. The analytical expressions for effective coefficients of laminated media with any finite number of anisotropic TMEE layers are explicitly obtained via the matrix notation. Such formulae can be applied to investigate the global behavior of functionally graded TMEE multilayers. The important case of bilaminates composites with anisotropic homogeneous phases is also expressed in a compact form using matrices and vectors depending on the individual geometrical and mechanical properties of the components. The case of a bilaminate with homogeneous transversely isotropic TMEE layers is studied. A chain of equalities relating all thermal (thermoelastic, pyroelectric, pyromagnetic and heat capacity) effective coefficients was found for the example corresponding to a parallel connectivity. An analytical formula to estimate the volume fraction for which the pyroelectric and pyromagnetic effects realize their extreme values is given. Comparisons with recently published results are included.

Thermoelastic stress analysis with a compact low-cost microbolometer system

Abstract: This article describes the development and validation of a novel thermoelastic stress analysis (TSA) system based on a low-cost microbolometer device. The use of a microbolometer for a highly synchronous and delicate temperature measurement breaks a longstanding and exclusive reliance on high performance, cooled photon detectors for thermoelastic applications. It is shown that despite markedly inferior noise equivalent temperature detectivity and dynamic response specifications, microbolometers are capable of achieving comparable levels of stress measurement performance. The practical implications for experimental stress analysis are significant. Microbolometers are relatively low in capital cost, small in size, have good tolerance to shock and vibration and consume less power than their photon counterparts, attributes that confer enormous practical advantages. It is argued that the emergence of TSA systems that are more affordable and better suited to in-service application could help to promote a much b...

Nonlinear thermoelastic analysis of thick-walled functionally graded piezoelectric cylinder

Abstract: This research addresses the nonlinear behavior of a functionally graded piezoelectric (FGP) cylinder under thermal, mechanical and electrical loads. Except the Poisson ratio, the other thermal, mechanical and electrical properties vary continuously along the thickness direction. The geometric nonlinearity was considered in strain–displacement relation. The present paper proposes a novel analytical method for estimating the response of the systems of nonlinear differential equations. The proposed method is modification and combination of Adomian’s decomposition and successive approximation methods. The governing nonlinear differential equations were solved using the proposed analytical method. The nonlinear solutions were presented for different values of nonhomogenous index. For validation of the results and justifying the necessity of the present study, the present results were compared with results obtained using the linear analysis. Due to using the functionally graded cylinder in serious environments such as chemical and weapon equipments or adjustable and precise condition, a nonlinear analysis for these materials is necessary. A nonlinear analysis improves the results significantly. A maximum of 5% improvement for electric potential and 9% for radial displacement were attained employing this nonlinear analysis rather than a linear analysis. These considerable improvements can present a confidence and adjustable tool for manufacturing and design of sensors and actuators with better accuracy.

Effect of anisotropy on Fatigue properties of AA2198 Al-Li plates joined by Friction Stir Welding

Abstract: Al-Li alloys are characterized by a strong anisotropy in mechanical and microstructural properties with respect to the rolling direction. In the present paper sheets, 4 mm thick, of AA2198 Al-Li alloy were joined via Friction Stir Welding (FSW) by employing a rotating speed of 1000 RPM and a welding speed of 80 mm/min, in parallel and orthogonal direction with respect to the rolling one. The joint mechanical properties were evaluated by means of tensile tests at room temperature. In addition, fatigue tests were performed by using a resonant electro-mechanical testing machine under constant amplitude control up to 250 Hz sinusoidal loading. The fatigue tests were conducted in axial control mode with R=?min/?max=0.33, for all the welding and rotating speeds conditions. The damage behavior was studied by applying thermoelastic stress analysis (TSA) to the crack formation and propagation of friction stir welded sheets under cyclic fatigue tests. The fatigue crack propagation experiments were performed on single edge notched specimens. Fatigue tests were carried out up to failure in tension- tension with load ratio R=0.33. The TSA measurement system allowed crack evolution to be observed in real-time during fatigue cycles and stress fields to be derived on the specimens from the temperature variation. The thermoelastic data were used to measure the principal stresses and principal strains on the specimens surface and the crack growth rate during tests. All the results were validated by employing finite element analysis performed with ABAQUS software. SEM observations of the fractured surfaces were done to characterize the weld performances.

Micromachined polycrystalline diamond hemispherical shell resonators

Abstract: The hemispherical resonator gyro (HRG) is low loss and high stability, spurring recent interest in micro-scale hemispherical resonators. To achieve mode-matching and high-Q performance in a hemispherical resonator, geometric symmetry in combination with low thermoelastic damping structural material are critical. In this work, we describe the development of millimeter scale 3D hemispherical shell resonators fabricated from polycrystalline diamond, a material with low thermoelastic damping and very high stiffness. The relation between the fourth harmonic (4θ) in a Fourier analysis of the resonator's radius r(θ) and frequency mismatch (Δf) of the 2θ elliptical vibration modes of the shell resonator is demonstrated.

A model for finite-deformation nonlinear thermomechanical response of single crystal copper under shock conditions

Abstract: A physically consistent framework for combining pressure–volume–temperature equations of state with crystal plasticity models is developed for the application of modeling the response of single and polycrystals under shock conditions. The particular model is developed for copper, thus the approach focuses on crystals of cubic symmetry although many of the concepts in the approach are applicable to crystals of lower symmetry. We employ a multiplicative decomposition of the deformation gradient into isochoric elastic, thermoelastic dilation, and plastic parts leading to a definition of isochoric elastic Green-Lagrange strain. This finite deformation kinematic decomposition enables a decomposition of Helmholtz free-energy into terms reflecting dilatational thermoelasticity, strain energy due to long-range isochoric elastic deformation of the lattice and a term reflecting energy stored in short range elastic lattice deformation due to evolving defect structures. A model for the single crystal response of copper is implemented consistent with the framework into a three-dimensional Lagrangian finite element code. Simulations exhibit favorable agreement with single and bicrystal experimental data for shock pressures ranging from 3 to 110 GPa.

Nonlinear Eulerian thermoelasticity for anisotropic crystals

Abstract: A complete continuum thermoelastic theory for large deformation of crystals of arbitrary symmetry is developed. The theory incorporates as a fundamental state variable in the thermodynamic potentials what is termed an Eulerian strain tensor (in material coordinates) constructed from the inverse of the deformation gradient. Thermodynamic identities and relationships among Eulerian and the usual Lagrangian material coefficients are derived, significantly extending previous literature that focused on materials with cubic or hexagonal symmetry and hydrostatic loading conditions. Analytical solutions for homogeneous deformations of ideal cubic crystals are studied over a prescribed range of elastic coefficients; stress states and intrinsic stability measures are compared. For realistic coefficients, Eulerian theory is shown to predict more physically realistic behavior than Lagrangian theory under large compression and shear. Analytical solutions for shock compression of anisotropic single crystals are derived for internal energy functions quartic in Lagrangian or Eulerian strain and linear in entropy; results are analyzed for quartz, sapphire, and diamond. When elastic constants of up to order four are included, both Lagrangian and Eulerian theories are capable of matching Hugoniot data. When only the second-order elastic constant is known, an alternative theory incorporating a mixed Eulerian–Lagrangian strain tensor provides a reasonable approximation of experimental data.