Showing papers on "Thermoelastic damping published in 1981"

Directivity patterns of laser‐generated ultrasound in aluminum

Abstract: Directivity patterns of laser‐generated longitudinal and shear waves in aluminum have been determined experimentally, for laser power densities both above and below the threshold for plasma formation on the target’s surface. Comparison of experimental results with theory has allowed generation mechanisms to be identified. Thermoelastic mechanisms predominate in the absence of a plasma, where stresses parallel to the surface are a dominant source characteristic. At higher power densities, momentum transfer from ablating material becomes more important, leading to a source with normal drive components.

A mathematical model for consolidation in a thermoelastic aquifer due to hot water injection or pumping

Abstract: A mathematical model is developed for the areal distribution of fluid pressure, temperature, land subsidence, and horizontal displacements due to hot water injection into thermoelastic confined and leaky aquifers. The underlying assumption is that the aquifer is thin in relation to the horizontal distances of interest, and hence all dependent variables of interest are average (over the thickness) values. The solid matrix is assumed to be thermoelastic. Following the development of three-dimensional conservation of mass and energy equations and equilibrium equations in terms of horizontal and vertical displacements, the mathematical model is derived by averaging the three-dimensional model over the vertical thickness of the aquifer, subject to conditions of plane total stress. The effects of viscous dissipation and compressible work have been included in the formulation. The resulting averaged coupled equations are in terms of pore water pressure, temperature, and vertical and horizontal displacements which are functions of x, y, and t only. The equations are nonlinear and have to be solved simultaneously due to the coupling that exists among them. Equations and appropriate boundary conditions in radial coordinates have also been presented for an example of a single injecting (or pumping) well.

Generalized one-dimensional thermal-shock problem for small times

Abstract: This paper is concerned with the one-dimensional problem of distribution of thermal stresses and temperature in the generalized thermoelastic semispace subjected 10 sudden heating with constant temperature on the bounding plane. The Laplace transform technique is used to solve the problem. The inverse transforms are obtained in an approximate manner as proposed by Paria |19| and Hetnarski |5|. Numerical computations for two particular cases are carried out for small values of lime, and the results are compared with the corresponding solution of the coupled problem obtained by Hetnarski |5|.

Thermoelasticity of circular cylindrical shells laminated of bimodulus composite materials

Abstract: Closed-form and finite-element solutions are presented for the thermoelastic behavior of laminated composite shells. The material of each layer is assumed to be thermoelastically orthotropic and bimodular, that is, having different properties depending upon whether the fiber-direction normal strain is tensile or compressive. The formulations are based on the thermoelastic generalization of Dong and Tso 's laminated shell theory, which includes thickness shear deformations. The finite element used here has five degrees of freedom per node (three displacements and two bending slopes). Numerical results are presented for deflections and the positions of the neutral surfaces associated with bending along both coordinate directions. The closed-form and finite-element results are found to be in good agreement.

Some Considerations on Thermal Shock Problems in a Plate

Abstract: Manson has given a well-known conventional approach to thermal shock problems in a plate. In his investigation, however, the inertia term and the thermomechanical coupling term were neglected in the governing field equations. As a result, the treatment became quasi-static, and then it was inadequate to model thermal shock problems having a steep time-gradient in the thermal and mechanical fields. In the present paper, we examine a rigorous treatment to find the exact solution for thermal shock problems in a plate when the following two effects are taken into account: (a) Dynamic treatment due to the presence of an inertia term. (b) A coupled thermal stress problem in the presence of a thermoelastic coupling term. Thus we can determine the significance of these effects on the thermal stress distribution when a sudden change of temperature occurs.

A note on the theory of thermoelastic damping

Abstract: This paper consists of three parts. In the first part, the problem of the conversion of mechanical energy into heat is treated, while in the second a general theory of thermoelastic friction in three-dimensional finite bodies is developed. In the third part, explicit results are obtained for thermoelastic damping in vibrating elastic beams. All investigations are based on the linear theory of thermoelasticity.

Some simpler cases of the gibbs problem for thermoelastic solids

Abstract: Gibbs formulated a fairly general theory of equilibrium for solids in contact with fluids. As a special case, he included nonlinear thermoelasticity theory, in particular a theory of thermoelastic phase transitions. For such phenomena, thermodynamicists use a theory which seems somewhat different but in fact is quite similar. We seek to clarify the factors involved in phase transitions from the viewpoint of Gibbs' theory.

Continuous martensitic transitions in thermoelastic solids

Abstract: This paper illustrates how thermoelasticity theory can be used to analyze a rather simple type of phase transition involving a shear critical point.

Stability of Thermoelastic Contact for the Aldo Model

Abstract: \"fA perturbation method is used to investigate the stability of a simple one-dimensional rod model of thermoeiastic contact which exhibits multiple steady-state solutions. A thermal contact resistance is postulated which is a continuous function of the contact pressure or separation. It is found that solutions involving substantial separation and/or contact pressures are always stable, but these are separated by unstable \"imperfect contact\" solutions in which one of the rods is very lightly loaded or has a very small separation. The results can be expressed in terms of the minimization of a certain energy function.\"]

The thermoelastic phase transition in Au—Cd alloys studied by acoustic emission

Abstract: The acoustic emission generated during the thermoelastic phase transitions in polycrystalline Au–47·5 at.% Cd and in Au–49 at.% Cd alloys has been recorded and analysed. It was found that the amount of acoustic activity depends upon the direction of the transformation, the heating or cooling rates, and the specific crystallographic features of the martensitic phases. Precursor acoustic activity was detected in both alloys at temperature differences of about 2 5°C before the M 8 point. The dynamics and kinetics of martensitic thermoelastic phase transformations are discussed in terms of the accompanying generation of acoustic emission.

A coupled, isotropic theory of thermoviscoplastic1ty based on total strain and overstress and its predictions in monotonic torsional loading

Abstract: A coupled, isotropic, infinitesimal theory of thermoviscoplasticity was proposed in [32, 33] and applied to a variety of simple loadings including both mechanical and thermal straining. In this paper we develop this theory by postulating specific forms of the mechanical constitutive equation and the internal energy rate. The heat conduction equation is then obtained from the internal energy rate and the first law of thermodynamics. The predictions of the theory in torsion are examined qualitatively and through numerical experiments. Torsion is simulated at loading rates differing by four orders of magnitude, and both jump-increases and jump-decreases in loading rate are also examined. The theory predicts an initial thermoelastic response followed by nonlinear, rate-dependent plastic behavior. The adiabatic temperature response in torsion is initially isothermal and is followed by inelastic heating. Significant differences are found between the mechanical responses to stress-and strain-controlled loading. ...

On a new method for axisymmetric coupled thermoelastic problems

Abstract: It is well known that the thermoelastic coupling term and the inertia term have to be taken into account in the treatment of problems involving a sudden change of temperature, such as thermal-shock problems. It is difficult to find the exact solution for coupled thermal-stress problems, and these have been solved only for the case of a one-dimensional temperature change such as in the semi-infinite regions. In the present paper, we show a new technique for the treatment of the coupled thermoelastic problem which can be applied to a two- or three-dimensional temperature field. As an illustration, we solve an axisymmetric coupled thermal-stress problem for an infinite solid cylinder with temperature changes in the radial and axial directions. The numerical results show that the thermoelastic coupling term has a considerable affect on the temperature and stress distributions.

Stability of nonlinear thermoelastic waves in membrane-like spinning disks

Abstract: General equations of motion and compatibility governing nonlinear transverse vibrations and waves in membrane-like isotropic spinning disks are derived, assuming the presence of a temperature field. A harmonic-type nonlinear wave is then studied, corresponding to the gravest mode in the linear case. Using the Galerkin procedure, the general wave frequency-wave amplitude relation is discussed for a disk with constant edge temperature and with faces freely transferring heat. By means of small temporal disturbances of transverse motions, leading to a system of two coupled differential equations related to a Mathieutype equation, a detailed analysis of wave stability is given. A numerical example is illustrated by a graph.

System Approach to the Thermal Behavior and Deformation of Machine Tool Structures in Response to the Effect of Fixed Joints

Abstract: Following the theory of nonlinear thermoelastic behavior of structural joints, developed recently by the authors, the conditions of heat transfer between contacting elements are analyzed. Two cases are considered: a hypothetical case in which no interactions take place at the joint, and a realistic one with the interactions in effect. Analysis of the structure response to the effect of the joint is carried out through the system theory, which is a new way to approach this problem. It is revealed that due to the interactions at the joint, the structure behaves thermally as a second order system, and not as a first order system. The latter would be the case if the nonlinear thermoelastic behavior of the joint were neglected. This finding, obtained in general terms, indicates that the thermal deformation of machine tool structures can vary nonmonotonically with time. This was verified through a computer simulated case study and was confirmed by existing experimental data.

Influence of the size factor on the thermal shock resistance of ceramic samples

Abstract: The cracking of brittle samples having suffered thermal shocks may be calculated by using the thermoelastic theory. This theory leads to a size effect, which is not always verified by experiments. The use of acoustic methods of characterization, for samples of various shapes and sizes, shows the size effect, but the experimental ΔTc values are greater than the calculated ones. This discrepancy must be due both to an overestimation of the A coefficient and an underestimation of the R parameter.

Thermoelastic and Dynamic Phenomena in Seals.

Abstract: : An analysis of a seal model is made where the rotating element has both fixed tilt and two-lobe waviness. The stator is assumed to be gimbal mounted and to have inertial mass. Hydrodynamic lubrication is assumed, following the short bearing or narrow seal model. Conditions are examined where the stator precesses in synchronism with the rotor rotation. Particular interest is given to operating conditions where such behavior appears to degenerate. (Author)

On generalized thermoelastic dielectrics

Abstract: A complete nonlinear constitutive theory of thermoelastic dielectrics including polarization effects is derived by using a modified entropy production inequality proposed by Green and Laws [1] and independently by Suhubi [2].∗ The constitutive equations of thermorigid dielectrics are also obtained. Results indicate that the thermodynamic temperature does not only depend on temperature and temperature rate but also on the polarization vector.

Optimum Distribution of Additive Damping for Vibrating Beam Structures

Abstract: : Cost and weight effectiveness of concentrated and distributed additive damping has been studied for linear systems (discrete and continuous) under prescribed harmonic loads and/or displacements. Increases in stiffness and mass due to the additive damping are included. Redistribution of an initially uniformly applied additive damping (viscoelastic layer) has been numerically and experimentally investigated for beam structures. An optimal redistribution has typically been found to reduce amplitudes of resonant responses by about 50 percent (level reduction by 6 dB) with the cost or weight of the damping treatment kept constant. One application has been to vibration isolation of a damped skeletal light-weight machine foundation. (Author)