Showing papers on "Thermoelastic damping published in 1975"

A note on thermoelastic strains and tilts

Abstract: The thermoelastic effects of a traveling wave of temperature on the surface of an infinite homogeneous elastic half space are examined. The horizontal and shear strain and the tilt are principally caused by tractions in the thermal boundary layer, and they decay vertically with the scale of the horizontal wavelength of the applied temperature wave. The vertical strain is larger at the surface by the ratio of this wavelength to the thermal boundary thickness, but below the boundary layer it behaves like the other components. The burial of instruments at practical depths is unlikely to reduce significantly the thermoelastic effects except on the vertical strain.

Thermoelastic waves generated by laser beams of low power

Abstract: A modulated or chopped beam from an argon ion laser, with CW power at the 1−W level, is used to generate thermoelastic waves in several liquids. The ceramic cylinder surrounding the liquids is the transducer for the acoustic waves. Output signal is measured as a function of frequency, with different laser powers and different amounts of absorption in the liquids. The analysis makes use of thermoelastic potentials in the liquid and in the ceramic cylinder, with appropriate continuity conditions between the two regions, and predicts results in good agreement with those measured. Conversion efficiency from laser power to acoustic power is extremely low at this power level, but increases directly with the laser power. Thus it is concluded that the acoustic wave generated by a modulated laser beam at the 1−W level propagating through sea water would only be detectable near the beam, but for a pulsed beam at the megawatt level, acoustic power might be detectable for several kilometers.Subject Classification: 35.65.

Elastic and thermoelastic constants of nepheline

Abstract: The single‐crystal elastic constants, their temperature coefficients, and the thermal expansion coefficients of natrual nepheline, (KAlSiO4)(NaAlSiO4)3, have been measured. The longitudinal modulus c11 and the shear modulus c66 have positive temperature coefficients. Since this implies the existence of a wide range of directions with a zero temperature coefficient of the ultrasonic travel time, nepheline may be a suitable substrate for ultrasonic surface‐wave signal processing devices.

Thermomechanical Characteristics of Alloys Exhibiting Martensitic Thermoelasticity

Abstract: Successful application of unique mechanical effects related to thermoelastic martensite transformation, deformation, and reversion is discussed in terms of the requirements to characterize various unique thermomechanical parameters, such as reversion stress, strain limits, stress and strain stability, and cycling effects. The dependence of reversion stress on such factors as prestrain, partial relaxation during reversion, temperature, and time is evaluated for Ni-Ti-base alloys and recent data are correlated with existing data for NiTi and other “shape-memory effect” alloys. The kinetics of martensitic deformation and reversion is discussed and related to proposed microstructural models for martensitic thermoelastic effects. Practical considerations such as stress relaxation, consequences of exceeding strain limits, and conditions for development of reversible effects are discussed. The general prerequisites for thermoelastic martensite effects are summarized, and implications regarding applications are discussed.

Thermodynamic considerations of " solid state engines" based on thermoelastic martensitic transformations and the shape memory effect

Abstract: Engine applications of the shape memory ("Marmem" ) effect associated with thermoelastic transformations are discussed. Such devices potentially enable the direct conversion of heat(i.e., solar energy or waste heat) into mechanical work. It is shown that efficiencies on the order of 20 pct may be expected and can be improved with alloys having certain transformation hysteresis loop characteristics.

Thermoelastic stability of laminated orthotropic circular plates

Abstract: Axisymmetric stability and thermal-buckling equations are established for circular plates composed of polarorthotropic layers subjected to mechanical loads depending only onr and thermal fieldsT=T(r, z). Alternative fourth order systems of two coupled differential equations are suggested in terms of the slope β andeither the radial displacementu or a stress function Ψ. The eigenvalue problem is formulated for quasi-heterogeneous composite plates and a closed-type solution is given for certain thermal-buckling problems in the form of Bessel functions of first kind and fractional order. Possibility of an analogy between a thermal and mechanical stability problem is shown and variation of eigenvalues with anisotropy parameters is noted. Numerous examples are presented indicating that suitable lamination of composite circular plates may transcend the buckling loads of individual constituents.

Thermal Calculations for Bridge Design

Abstract: A straightforward method is shown for calculating thermal stresses in bridges. Unsteady temperature distributions are obtained from numerical solutions of the one-dimensional unsteady heat equation, and comparison with experiment seems to validate the simplifying assumption that horizontal heat movements are small enough to be ignored. Stresses are calculated by solving a two-dimensional thermoelastic problem, and a design example shows that stresses calculated in this way can be significantly larger than stresses calculated by ignoring the coupling effect between longitudinal and lateral stresses.

Lattice Softening and the Origin of SME

Abstract: “Lattice softening” or “Soft shear mode” has recently been found in connection with the displacive or martensitic phase transition in thermoelastic alloys and compounds. It is here described that in the β1, (ordered bcc) alloys such as CuAuZn2 and AuCd, the lattice softening appears as a premonitory phenomenon in thermoelastic martensitic transformation and it has an intimate relation to the essential characters (shear mechanism and nucleation) of the thermoelastic martensite. Moreover, the lattice softening is found to be fundamental for understanding the mechanism of the socalled “pseudoelasticity” (superelastic and ferroelastic behaviour), which has been observed to be closely related to SME. The present author suggests that the origin of SME might be contained in the superelastic behaviour, which is a unique stress-strain feature observed upon deformation of both the β1, and martensite phases. In order to make clear the origin of SME, therefore, it is most important to account for the role of lattice softening upon the mechanism of this superelastic behaviour, which basic nature may be due to the existence of coherent boundaries, such as mobile twin or domain boundaries in the martensite crystal and also interfaces between the stress-induced martensite and the β1, (matrix) crystal.

Thermoelastic Vibration and Damping for Circular Timoshenko Beams

Abstract: Within the framework of the theories of coupled linear thermoelasticity and Timoshenko beams, the vibration and thermoelastic damping (with emphasis on the transverse ones) of circular cross-section beams are studied. The governing equations are derived for the case of general mechanical boundary conditions and special thermal boundary conditions that follow the Newton surface heat transfer law. A variational principle governing the eigenfunctions associated with an eigenvalue is formulated. An exact solution, together with the thermoelastic damping coefficient, is obtained for the case of transverse vibrations of a simply supported beam with lateral surfaces thermally insulated and end surfaces kept at constant temperature. Numerical results, together with the discussion for the first two eigenvalues and the thermoelastic damping coefficients, are also presented.

Laser‐generated thermoelastic shock wave in liquids

Abstract: In the present investigation the procedure of matched asymptotic expansion has been applied to obtain a higher approximation for the flow of an incompressible second‐order fluid past a porous sphere. The boundary conditions have been satisfied by matching Stokes (inner) and Oseen (outer) solutions of the stream function. The terms in the inner expansion are the solutions of nonlinear partial differential equations which have been solved approximately by expanding in terms of a non‐Newtonian parameter S, which is small. The drag experienced by the sphere has been obtained and is discussed for a few particular cases.

Steady-state thermal stresses in an elastic solid containing an insulated penny-shaped crack

Abstract: A solution is given for the steady-state thermal stress and displacement field in an infinite elastic solid containing an insulated penny-shaped crack. The problem is reduced to a mixed-boundary-value problem for the half-space, making use of Green's isothermal solution for the thick elastic plate in complex harmonic potentials and a particular thermoelastic solution due to Williams. In the axisymmetric case, the complex potential reduces to the real harmonic function used by Shail in his solution for the external crack.To illustrate the use of the method in both axisymmetric and non-axisymmetric problems, complete solutionsare given for (1) a uniform heat flow and (2) a linearly varying heat flow disturbed by an insulated penny-shaped crack.

A review: Quasistatic thermal stresses in anisotropic elastic bodies, with applications to composite materials

Abstract: Following a brief review of the governing equations of classical thermoelasticity, several commonly used methods of solutions are discussed, and a survey is made of thermoelastic boundary value problems which appear in the literature. References are also given to investigations concerned with the prediction of effective thermo-elastic coefficients for composites, and to studies of the average and local thermal stresses in reinforced structures. Finally, a few recently developed continuum theories which take into account the microstructure of composite materials are cited.

Damping of elastic surface waves by density fluctuation on solid surfaces

Abstract: We investigate theroetically the damping rate of elastic surface waves due to density fluctuation on solid surfaces. A formula for the damping rate is presented using the Green’s function. The frequency and correlation length dependence of the rate is calculated. The results show a frequency and correlation length dependence quite different from that of the bulk phonon case.

Elastic and thermoelastic media in general relativity

Abstract: This article is a study of elastic media in general relativity; it is based on a relativistic generalization of the functional constitutive equations of continuous media of Truesdell and Noll. We show that it is possible to give a definition of hyperelasticity in general relativity, on condition that the existence of a reference state of minimum free energy is postulated. This approach allows us also on the one hand to study the case of relativistic elasticity under high pressure (cf. certain stellar models), and on the other hand to study thermoelastic media without the paradox of infinite velocity of heat conduction.

Damping in dynamic structure-foundation interaction

Abstract: Two methods of calculating the damping ratio for structures on compliant foundations are presented. One method employs the calculation of the system damping ratio from the dynamic amplification factor, the other the modal damping ratio from energy considerations. The numerical results for both methods are compared and interpreted. Three sources of damping are considered: inter-storey damping, radiation damping, and foundation material damping. The numerical results demonstrate that with the introduction of compliant foundations the damping ratio of the system can be larger or smaller than that of the corresponding fixed-base structure. Material damping in the foundation soil has been shown to contribute significantly to the over-all damping ratio.