Analysis of Surface Wave Generation by Laser Interference

1990 ◽  
Vol 57 (2) ◽  
pp. 415-418 ◽  
Author(s):  
K. J. Faran ◽  
R. J. Dwayne Miller ◽  
S. M. Gracewski
Keyword(s):  
Rapid Heating ◽  
Free Edge ◽  
Elastic Half Space ◽  
Temperature Fields ◽  
Thermal Excitation ◽  
Complex Frequency ◽  
Branch Points ◽  
Laser Interference ◽  
Wave Speeds ◽  
Branch Cuts

An analytical solution for thermal excitation of elastic waves in an homogeneous, isotropic, elastic half-space resulting from a pulsed laser interference pattern incident on the solid surface is presented. The spacially-periodic laser field absorbed by the surface causes rapid heating within the optical penetration depth. Thus, a temperature field is generated which can be modeled as being spacially harmonic along the free edge, decaying exponentially with depth, and having a Heaviside dependence on time. Transform techniques yield expressions for the resulting transverse and normal displacements within the laser interference region in terms of infinite integrals over frequency. The integrands contain poles indicating the expected Rayleigh waves propagating along the surface, as well as branch points corresponding to the bulk longitudinal and transverse wave speeds. The solution is obtained by integrating numerically in the complex frequency plane with an appropriate contour around the poles and branch cuts. Normal and transverse displacements are plotted as functions of time and depth for various materials and temperature fields.

Numerical and Experimental Analysis of Laser Surface Remelting of Al 9wt% Si Alloy Samples

2008 ◽  
Vol 587-588 ◽  
pp. 721-725
Author(s):  
Noé Cheung ◽  
Kleber A.S. Cruz ◽  
Noman H. Khan ◽  
Amauri Garcia
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Rapid Heating ◽  
Thermal Action ◽  
High Energy ◽  
Laser Surface ◽  
High Energy Density ◽  
Temperature Fields ◽  
Laser Materials ◽  
Laser Surface Remelting

Laser materials processing has been widely applied in industrial processes due to unique precision and very localized thermal action furnished by the laser’s high energy density and power controllability. With the inherent rapid heating and cooling rates to which this surface layer is subjected, this process provides an opportunity to produce different microstructures from that of the bulk metal leading to useful properties. The aim of this work is to develop a heat transfer mathematical model based on the finite difference method in order to simulate temperature fields in the laser surface remelting process. Convective heat transfer in the remelted pool is taken into account by using the effective thermal conductivity approach. Theoretical predictions furnished by previous models from the literature were used for validation of numerical simulations performed with the proposed model. Experiments of laser surface remelting of Al-9 wt pct Si samples was carried out in the present investigation, and numerical simulations was applied for the laser machine operating parameters. The work also encompasses the analysis of microstructural and microhardness variations throughout the resulting treated and unmolten zones.

Influence of High Temperature Heat Sources on the Moisture and Temperature Distribution in a Real/Virtual Foundry Sand Mould

2016 ◽  
Vol 7 ◽  
pp. 69-83
Author(s):  
Paweł Popielarski ◽  
Zenon Ignaszak
Keyword(s):  
Cast Iron ◽  
Physical Properties ◽  
Rapid Heating ◽  
Temperature Fields ◽  
Coupled Modeling ◽  
Molding Sand ◽  
Mould Material ◽  
Sand Mould ◽  
Thermal Phenomena ◽  
Thermo Physical Properties

The problem described in the paper concerns the thermo-physical properties of the green mould material to which the cast iron is most often poured. The study includes the experiment of pouring the cast iron plate into green bentonite-sand mould. The temperature fields of casting and in different zones of the mould were recorded. The goal of the study was to determine the substitute thermo-physical properties of mould sand containing the over-moisture zone by means of simulation tests (inverse problem). An originality of the related research is an attempt to take into account the effects of the global thermal phenomena occurring in the quartz sand bonded by bentonite-water binder, by application of the substitute thermal coefficients without using the coupled modeling. In the simulation tests in order to achieve the effect of rapid heating of the mould (below temperatures 100 °C) by poured cast iron (T>1300 °C), the function of the latent heat source and the modified values of substitute thermal conductivity and substitute specific heat of the molding sand were used. In order to facilitate the solution, the mould was divided into zones, in which different starting humidity of molding sand was assumed.

Transient Green’s Function Behavior for a Prestressed Highly Elastic Half-Space

2000 ◽  
Vol 68 (2) ◽  
pp. 162-168 ◽  
Author(s):  
L. M. Brock
Keyword(s):  
Half Space ◽  
Rayleigh Waves ◽  
Arbitrary Constant ◽  
Elastic Half Space ◽  
Normal Surface ◽  
Poisson Effect ◽  
Wave Speeds ◽  
Wave Patterns ◽  
Infinitesimal Deformations ◽  
Surface Loads

A plane-strain study of a prestressed isotropic compressible neo-Hookean half-space subjected to shear and normal surface loads is performed. The loads are either stationary and applied for an instant, or travel at an arbitrary constant speed. The transient process is viewed as the superposition of infinitesimal deformations upon large, and exact expressions for the displacements, within and upon, the half-space are obtained. These, and the associated wave patterns, demonstrate the anisotropy induced by prestress. The wave speeds themselves are sensitive to prestress; in particular, Rayleigh waves disappear beyond a critical compressive prestress. A critical tensile prestress also exists, beyond which a negative Poisson effect occurs.

scholarly journals Quasinormal modes in charged fluids at complex momentum

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Aron Jansen ◽  
Christiana Pantelidou
Keyword(s):  
Quasinormal Modes ◽  
Quantitative Agreement ◽  
Dispersion Relations ◽  
Radius Of Convergence ◽  
Complex Frequency ◽  
Branch Points ◽  
Charged Fluids ◽  
Hydrodynamic Modes ◽  
Momentum Plane ◽  
The One

Abstract We investigate the convergence of relativistic hydrodynamics in charged fluids, within the framework of holography. On the one hand, we consider the analyticity properties of the dispersion relations of the hydrodynamic modes on the complex frequency and momentum plane and on the other hand, we perform a perturbative expansion of the dispersion relations in small momenta to a very high order. We see that the locations of the branch points extracted using the first approach are in good quantitative agreement with the radius of convergence extracted perturbatively. We see that for different values of the charge, different types of pole collisions set the radius of convergence. The latter turns out to be finite in the neutral case for all hydrodynamic modes, while it goes to zero at extremality for the shear and sound modes. Furthermore, we also establish the phenomenon of pole-skipping for the Reissner-Nordström black hole, and we find that the value of the momentum for which this phenomenon occurs need not be within the radius of convergence of hydrodynamics.

scholarly journals An asymptotic hyperbolic–elliptic model for flexural-seismic metasurfaces

2019 ◽  
Vol 475 (2227) ◽  
pp. 20190079 ◽  
Author(s):  
P. T. Wootton ◽  
J. Kaplunov ◽  
D. J. Colquitt
Keyword(s):  
Half Space ◽  
Elastic Half Space ◽  
Asymptotic Model ◽  
Junction Conditions ◽  
Scalar Wave ◽  
Elastic Surface ◽  
Wave Speeds ◽  
Closed Form Solutions ◽  
Elliptic Model ◽  
Thin Beams

We consider a periodic array of resonators, formed from Euler–Bernoulli beams, attached to the surface of an elastic half-space. Earlier studies of such systems have concentrated on compressional resonators. In this paper, we consider the effect of the flexural motion of the resonators, adapting a recently established asymptotic methodology that leads to an explicit scalar hyperbolic equation governing the propagation of Rayleigh-like waves. Compared with classical approaches, the asymptotic model yields a significantly simpler dispersion relation, with closed-form solutions, shown to be accurate for surface wave-speeds close to that of the Rayleigh wave. Special attention is devoted to the effect of various junction conditions joining the beams to the elastic half-space which arise from considering flexural motion and are not present for the case of purely compressional resonators. Such effects are shown to provide significant and interesting features and, in particular, the choice of junction conditions dramatically changes the distribution and sizes of stop bands. Given that flexural vibrations in thin beams are excited more readily than compressional modes and the ability to model elastic surface waves using the scalar wave equation (i.e. waves on a membrane), the paper provides new pathways towards novel experimental set-ups for elastic metasurfaces.

scholarly journals Exponentially Decaying Pressure Pulse Moving With Constant Velocity on the Surface of a Layered Elastic Material (Superseismic Layer, Subseismic Half Space)

1970 ◽  
Vol 37 (1) ◽  
pp. 141-152 ◽  
Author(s):  
J. P. Wright ◽  
M. L. Baron
Keyword(s):  
Half Space ◽  
Constant Velocity ◽  
Moving Load ◽  
Elastic Half Space ◽  
Normal Surface ◽  
Entire Plane ◽  
Normal Loading ◽  
Wave Speeds ◽  
S Waves ◽  
Typical Configuration

The response of a layered elastic half space to a progressing exponentially decaying normal surface pressure is evaluated for a case in which the constant velocity V of the moving pressure is greater than that of the P and S waves, respectively, in the upper layer (superseismic) and smaller than these wave speeds in the underlying half space (subseismic). It is assumed that a steady state exists with respect to coordinate axis attached to the moving load. The superseismic-subseismic geometry results in a stress field that extends over the entire plane, with sharp shocks possible only in that portion of the layer that lies behind the front of the progressing normal loading. A computer program for evaluating stresses and velocities at points in the medium was developed and results are presented for a typical configuration of interest.

Bending of a Cantilever Plate Supported From an Elastic Half Space

1961 ◽  
Vol 28 (3) ◽  
pp. 387-394 ◽  
Author(s):  
N. C. Small
Keyword(s):  
Half Space ◽  
Plate Theory ◽  
Free Edge ◽  
Fourier Integral ◽  
Elastic Half Space ◽  
Cantilever Plate ◽  
Classical Plate Theory ◽  
Small Deviations ◽  
Shear Effects ◽  
The Moment

A solution is obtained for an infinitely long cantilever plate supported from an elastic half space. The junction conditions between the elasticity approach for the half space and the classical plate theory (no-shear) approach for the plate are based upon the use of assumed equilibrium surface tractions for the half space. The formal Fourier integral results for the example of a concentrated free-edge load are evaluated using an IBM 704 computer. The correlation with the deflection results of a steel model test is shown to be very good. The small deviations from the theoretical values are primarily due to shear effects in the model. It is also shown that, except for very stubby plates, it is sufficiently accurate to neglect the shear effects along the half space, and to assume that the rotation is proportional to the moment in the conventional “Winkler” sense.

The growth of mica polytypes as studied by conventional and high-resolution TEM

1983 ◽  
Vol 41 ◽  
pp. 174-177
Author(s):  
A. Baronnet ◽  
M. Amouric
Keyword(s):  
Water Pressure ◽  
Point Of View ◽  
Temperature Fields ◽  
Natural Occurrence ◽  
Growth Mechanisms ◽  
Long Period ◽  
High Resolution Tem ◽  
Layer Stacking ◽  
Experimental Works ◽  
Potential Use

The origin of mica polytypes has long been a challenging problem for crystal- lographers, mineralogists and petrologists. From the petrological point of view, interest in this field arose from the potential use of layer stacking data to furnish further informations about equilibrium and/or kinetic conditions prevailing during the crystallization of the widespread mica-bearing rocks. From the compilation of previous experimental works dealing with the occurrence domains of the various mica "polymorphs" (1Mr, 1M, 2M1, 2M2 and 3T) within water-pressure vs temperature fields, it became clear that most of these modifications should be considered as metastable for a fixed mica species. Furthermore, the natural occurrence of long-period (or complex) polytypes could not be accounted for by phase considerations. This highlighted the need of a more detailed kinetic approach of the problem and, in particular, of the role growth mechanisms of basal faces could play in this crystallographic phenomenon.

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