Showing papers on "Thermoelastic damping published in 1977"
TL;DR: In this paper, the authors used a scannable laser to generate elastic waves for flaw detection in a metallic sample and reported an increase of up to 46 dB at 20 MHz over that generated from a free surface.
Abstract: Repetitive pulses from lasers with pulse widths 5–10 nsec or a current generator with 10–25‐nsec widths have been used to launch acoustic waves by thermoelastic expansions. For the laser case, when transparent media such as quartz plates are used to acoustically constrain the energy absorbing surface, an increase of up to 46 dB at 20 MHz was observed over that generated from a free surface. An experiment using a scannable laser to generate elastic waves for flaw detection in a metallic sample is described.
158 citations
TL;DR: In this article, a microscopic Hamiltonian that takes into account single particle orientational potential effects and rotational-translational coupling in molecular crystals is derived, which leads to an effective orientational interaction between nonspherical molecules.
Abstract: Starting from a repulsive overlap potential, we derive a microscopic Hamiltonian that takes into account single particle orientational potential effects and rotational–translational coupling in molecular crystals. This coupling leads to an effective orientational interaction between nonspherical molecules. Theoretical expressions for the elastic constants in the presence of this interaction are derived. The anomalous thermoelastic behavior which was discovered by Haussuhl for c 44 and c 11 in KCN and NaCN, and found by Rowe e t a l. in neutron measurements of TA phonons, is explained. The qualitative and quantitative agreement between theory and experiment is convincing.
111 citations
TL;DR: In this paper, single crystals of fresnoite Ba 2 TiSi 2 O 8 with diameters up to 2 cm and lengths of 7 cm have been grown by Czochralski technique from a stoichiometric melt.
72 citations
62 citations
TL;DR: In this paper, the effects of the thermal boundary layer and surface topography on uniform slopes were investigated and it was shown that these effects can be considerably reduced by burying instruments at practical depths.
Abstract: Coupling between the thermal boundary layer and surface topography is an important source of thermoelastic tilts and strains. Simple formulas are given to compute these effects on uniform slopes. In contradiction to inferences derived from analyses for a semi-infinite half space, these effects can be considerably reduced by burying instruments at practical depths.
56 citations
TL;DR: In this paper, a microscopic Hamiltonian that takes into account single particle orientational potential effects and rotational-translational coupling in molecular crystals is derived, which leads to an effective orientational interaction between nonspherical molecules.
Abstract: Starting from a repulsive overlap potential, we derive a microscopic Hamiltonian that takes into account single particle orientational potential effects and rotational–translational coupling in molecular crystals. This coupling leads to an effective orientational interaction between nonspherical molecules. Theoretical expressions for the elastic constants in the presence of this interaction are derived. The anomalous thermoelastic behavior which was discovered by Haussuhl for c 44 and c 11 in KCN and NaCN, and found by Rowe e t a l. in neutron measurements of TA phonons, is explained. The qualitative and quantitative agreement between theory and experiment is convincing.
53 citations
47 citations
42 citations
TL;DR: The temperature dependence of all elastic constants of cubic NaCN, measured by ultrasonic methods at ca 15 MHz from the transition point at 10.55 to 200°C, exhibits a similar anomalous thermoelastic behaviour to cubic KCN as discussed by the authors.
Abstract: The temperature dependence of all elastic constants of cubic NaCN, measured by ultrasonic methods at ca 15 MHz from the transition point at 10.55 to 200°C, exhibits a similar anomalous thermoelastic behaviour to cubic KCN. Within a wide temperature range all elastic wave velocities increase with higher temperature. The most characteristic feature of the anomalous behaviour is the softening of the shear constant c44 approaching the transition temperature. It is given by c44(T) ≃O.2144(T- T0)/T0 (1011dyn cm-2) with T0 = 255.4 K. The extremely small velocity of the elastic transverse wave connected with c44 makes NaCN highly suited for acousto-optical deflector devices.
36 citations
19 May 1977
TL;DR: In this paper, the effect of friction on the dissipation of the energy of oscillation was investigated in a more complex system, including cases where an apparently hysteretic behaviour arises although the actual dissipative mechanism is frictional.
Abstract: Bridges subjected to dynamic testing have commonly shown relatively small variation of damping (expressed as the effective instantaneous logarithmic decrement) with amplitude This is clearly closer to the theoretical solution for viscous or idealised hysteretic damping than to the solution of the classic simple friction-damped system Nevertherless, the magnitude of the observed damping is such that in many cases friction must make a major contribution to the dissipation of the energy of oscillation Some indication is given of the possible magnitude of hysteretic effects, including cases where an apparently hysteretic behaviour arises although the actual dissipative mechanism is frictional To assist understanding of the way practical factors modify the classic friction damping model, the results are presented of an extended analysis of the effect of friction in more complex system /Author/
21 citations
TL;DR: In this paper, the influence of small thermoelastic coupling on the propagation of thermal wave disturbances in an infinite medium was investigated and the thermal relaxation time of heat conduction was included in the analysis to insure that the thermal waves propagate with finite signal speeds.
Abstract: Integral transform techniques are employed to study the influence of small thermoelastic coupling on the propagation of thermoelastic disturbances in an infinite medium. The thermal relaxation time of heat conduction is also included in the analysis to insure that the thermal waves propagate with finite signal speeds. Explicit expressions for the wave speeds and amplitudes are obtained. Numerical results are presented to illustrate the salient features of the problem.
TL;DR: In this article, a hierarchy of constitutive equations for materials with arbitrary symmetry by introducing various thermodynamic potentials was constructed for a linear thermoelastic dielectric, assuming dependence of the stored energy function on the strain tensor, the polarization vector and the polarization gradient tensor.
TL;DR: In this paper, the frequency and amplitude of the acoustic signals that are generated in human beings and laboratory animals were calculated using a previously developed thermoelastic models of microwave-induced auditory sensations.
Abstract: Previously developed thermoelastic models of microwave-induced auditory sensations are applied to calculate the frequency and amplitude of the acoustic signals that are generated in human beings and laboratory animals. Graphs of computed displacement and pressure as a function of time are presented for several species.
Journal Article•
TL;DR: In this paper, a phenomenological theory for the diffusion of a dilute solution of a gas in a thermoelastic solid is proposed, where the thermomechanical behavior of the solid is assumed to be unaffected by the presence of the gas.
Abstract: A phenomenological theory is proposed for the diffusion of a dilute solution of a gas in a thermoelastic solid. It is assumed that the thermomechanical behavior of the solid is unaffected by the presence of the gas. On the other hand the presence of the solid is recognized by the gas by letting certain thermomechanical variables of the solid to enter into the constitutive equations of the gas. The constitutive functionals of the gas are restricted by the principles of continuum physics. These principles are currently referred to as equipresence, material objectivity, entropy production inequality, as well as the balance equations of mass, linear and angular momentum and internal energy. By this approach, axiomatic statements on the existence of equations of state are avoided and the classical results of linear irreversible thermodynamics are obtained by further specialization of the proposed theory.
TL;DR: In this paper, the shape of the profile curve of a single crystal is obtained by the proper selection of a device which shapes the melt column which rises due to the capillary effect.
TL;DR: In this article, the elastic and thermoelastic constants of triglycine sulphate, point group 2/m, have been measured by ultrasonic methods between 55° and 75°C.
Abstract: All elastic and thermoelastic constants of triglycine sulphate, point group 2/m, have been measured by ultrasonic methods between 55° and 75°C. The elastic properties in the paraelectric and in the ferroelectric phases do not differ a great deal. The elastic as well as the thermoelastic properties of the paraelectric phase are highly anisotropic.
TL;DR: In this paper, a constitutive theory is established for a gas diffusing, as a dilute solution, in a linear thermoelastic solid, which is compatible with the laws of thermomechanics i.e., mass, momentum and energy balance.
Abstract: In part I of the present work a constitutive theory is established for a gas diffusing, as a dilute solution, in a linear thermoelastic solid. The theory is compatible with the laws of thermomechanics i.e., mass, momentum and energy balance, as well as with the principles of positive entropy production and material objectivity. The assumptions of small concentrations of the gas and the absence of viscous effects simplify the analysis considerably. This allows a thermomechanical model for the solid to be assumed, independent of the presence of the gas. The constitutive model adopted for the solid is the linear uncoupled theory of thermoelasticity. In this level of generality a transport theory is developed for the gas by using the conservation laws of mass, linear momentum and internal energy. Some uncommon identities for the thermodynamic quantities of the gas are also established, based on the derived functional dependence for the internal energy, entropy, free energy and stress tensor of the gas. Thus a Gibb's type equation is obtained. In addition a comparison with classical irreversible thermodynamics, previous intuitive theories and experiments is made.
TL;DR: The elastic moduli, their temperature derivatives, and the dynamic piezoelectric constants of trigonal potassium bromate, point group 3m, were measured by ultrasonic methods.
Abstract: The elastic moduli, their temperature derivatives, and the dynamic piezoelectric constants of trigonal potassium bromate, point group 3m, were measured by ultrasonic methods. The coupling coefficient k, for longitudinal waves which propagate parallel to the threefold axes is 0.58. As the damping coefficient for these waves is extremely small, even at high frequencies up to 100 MHz, trigonal potassium bromate is preferentially suitable for highly efficient generators and sensors of ultrasonic waves. The dielectric constants are relatively small and no disturbing electric conductivity occurs as, for example, in lithium iodate. Therefore this material is superior to most other crystals in its use for such devices. All thermoelastic constants are negative, and it is not possible to cut a crystal with temperature-independent properties.
TL;DR: In this article, two different morphologies, slender banded and spear shaped, are observed in cooled bulk specimens, both being thermo-elastic, and they exhibit a monoclinic 3R type stacking order structure with internal twins and stacking faults.
Abstract: Thermoelastic martensites formed upon subzero cooling a Ag-38 at. pct Zn alloy have been studied by means of optical and electron microscopy, electron diffraction, and electrical resistivityvs temperature measurements. Two different morphologies, slender banded and spear shaped, are observed in cooled bulk specimens, both being thermoelastic. The slender banded martensite is retained at room temperature in thin foils after subzero cooling and possesses the 9R type long period stacking order structure with internal stacking faults on the basal plane. This 9R martensite is “normal” with an orthorhombic lattice:a=4.81,b=2.82 andc=20.5A (a:b:c=1.71:1:7.27). The spear shaped martensite is also retained at room temperature in subzero cooled thin foils and in shape memory cycled ribbons as well. This morphology exhibits a monoclinic 3R type stacking order structure with internal twins and stacking faults. Lattice parameters of the 3R martensite area=4.83,b=2.87,c=6.94A and β=87.4 deg (a:b:c=1.68:1:2.41). This structure is equivalent to that of AuCuI (L10, fct) with lattice parametersa=4.07,c=3.89, andc/a=0.96. The twin and stacking fault planes in the 3R martensite are the (201) and (001) planes respectively. The basal planes of the 9R and 3R martensites are common, being generated from the {110} plane of the CsCl type parent phase, and the two martensites differ only in the shuffling mode on the {110} plane upon transformation. The thermelastic nature of the 3R martensite is slightly different from that of the 9R one.
01 Oct 1977
TL;DR: In this article, a thermo-elastic model of a laser irradiated plate is developed, which accounts for plate flexure and shear deformation as well as plate stretching.
Abstract: : A thermo-elastic model of a laser irradiated plate is developed. The model accounts for plate flexure and shear deformation as well as plate stretching. An exact solution in series form is found for the dynamic response of a circular plate clamped at its boundary. The plate is subjected to laser irradiation at its center, and normal to the plate surfaces. Experiments with a Holobeam model 630-Q Nd Laser were conducted to verify the mathematical model. A careful comparison between theory and experiment of transverse plate deflection induced by the Laser shows good agreement. (Author)
TL;DR: In this paper, general expressions for both amplitude-dependent and speed-dependent damping were derived as a function of nonlinear restoring forces and arbitrary nonlinear damping forces, and the results of the analysis suggest how experimental data can be utilized to identify and evaluate the damping parameters for a given non-linear oscillator.
Abstract: The logarithmic damping decrement is obtained as a function of arbitrary non-linear restoring forces and arbitrary, but small, non-linear damping forces. General expressions are obtained for both amplitude-dependent and speed-dependent damping. The special case of a cubic restoring force with quadratic amplitude-dependent damping and the special case of a cubic restoring force with quadratic speed-dependent damping are considered in detail. The results of the analysis suggest how experimental data can be utilized to identify and evaluate the damping parameters for a given non-linear oscillator.
TL;DR: In this paper, the problem of first strain gradient solid stability under non-cons rvative loadings is studied and an energy Liapunov functional is constructed and the sufficiency criteria for the stability of a loaded equilibrium configuration are derived.
Abstract: The problem of thermoelastic stability of a first strain gradient solid under noncons rvative loadings is studied. The Liapunov-Movchan method of elastic stability analysis is reviewed. An energy Liapunov functional is constructed and the sufficiency criteria for the stability of a loaded equilibrium configuration are derived. The effects of motion dependent surface tractions and couples are discussed. The special case of isothermal elastic stability of solids with couple stress is also considered.
TL;DR: In this paper, a first-ply failure design philosophy and employing a linear thermoelastic analysis was employed to find that taking temperature decrease effects into account leads to substantial weight penalties in strength critical fiber composite laminates.
Abstract: Results of a laminate optimization study, which includes prescribed temperature change and mechanical loading conditions, are presented. Minimum-weight designs for balanced symmetric laminates are obtained subject to strength, membrane stiffness, and minimum thickness requirements, while including and omitting temperature change effects. Based on a first ply failure design philosophy and employing a linear thermoelastic analysis, it is shown that taking temperature decrease effects into account leads to substantial weight penalties in strength critical fiber composite laminates. Numerical results are presented for representative fiber composite materials based on three commonly used combined stress failure criteria.