Grating holographic interferometry

A holographic interferometric technique, combining an image hologram with a grating approach, is proposed for three-dimensional deformation measurements on opaque planar object surfaces. In this technique, the holographic plate is brought close to the object surface, onto which a high-frequency crossed-line diffraction grating has been replicated. The grating surface produces multiple object waves rather than the usual diffusely reflected object waves. The double-exposed single holograms can be reconstructed at multiple off-axis angles. Four independent high-contrast fringe patterns are extracted simultaneously. Displacement vectors over the entire measurement area are separated in three orthogonal directions. The resultant displacements are presented as three-dimensional meshed plots and topographic contour maps. The optical system for both recording and reconstruction of the holograms has been simplified compared to conventional holographic interferometry. Experimental errors associated with fringe readout and system geometry are reduced because of the sharp images and the well-defined spatial orientation in the reconstruction system.     

A geometrical approach to holographic interferometry

Geometrical considerations are used to obtain quantitative data for the components of the displacement vector. Use is made of a dual-beam illumination and a variant is described, using point light sources and a single point of observation. Contour lines for the displacement vector in the viewing direction and in a perpendicular direction are obtained as the algebraic sum and difference of two interference patterns. Densification of the initial pattern is used to obtain moiré patterns for the out-of-plane and in-plane displacements of flat Surfaces and for the derivatives of these displacements. To determine the complete displacement field of objects of arbitrary shape, one holographic plate is sufficient, using two times two-point light sources.     

Application of the holographic interferometry method to determine the stress intensity factor

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 155–158, January–February, 1990.     

全息干涉法在条形药包离面位移场研究中的应用

以新型红宝石激光照相装置为基础,进行动态全息实验系统研究及设计,实现了一次爆破加载获取四个动态过程爆破模型的位移场条纹图,用此研究了线型载荷爆破时质点离面位移振动的变化规律。研究表明：端部延长线方向离面位移值在全场所有剖面始终最小,发现在线型载荷离面位移场和应力场一样,同样存在端部效应现象;中垂线上的最大位移值在不同时间都高于其它计算剖面位移极值;瑞利波产生的位移衰减很慢。     

Application of holographic interferometry to a study of wave propagation in rock

Holographic interferometry was utilized to determine the three orthogonal components of displacement in elastic surface waves. A pulsed ruby laser was used as the light source and techniques to improve its coherence properties are described. Procedures for the formation and reconstruction of the hologram, fringe interpretation, and data reduction and presentation are detailed. The elastic-wave velocities and material constants for pink westerly granite were obtained. Solutions for an explosively generated Rayleigh wave in a half space and its reflection from a free edge are presented.     

Application of the holographic interferometry in transport phenomena studies

 This article provides an overview of all the experimental research studies in the field of heat and mass transfer by means of the holographic interferometry which were performed under the supervision of Professor Franz Mayinger during his professorship. The principle objective of this paper is to contribute to the knowledge base of the heat and mass transfer processes in various fields as well as to illustrate the capabilities of the holographic interferometry. Investigations of the heat transfer pattern in grooved channels and in various geometries of compact heat exchangers, drying processes of a dispersed, water-based varnish on paper, mixed convection in bent ducts, the growth and condensation of vapor bubbles in subcooled boiling and the simultaneous heat and mass transfer are presented. The results of all these studies demonstrate the successful application of the holographic interferometry and Professor Mayinger's highly valuable contribution in this area. Received on 11 April 2001     

Some applications of holographic interferometry

Holographic interferometry, a new technique for measuring small displacements, is discussed. Application is made to the measure of surface displacements of strained bodies in two specific examples. The curvature of one face of a statically bent bar was examined in detail and compared with the three-dimensional elastic solution. In the second example, the radial-displacement field was measured in the area of the leading edge of a longitudinal compressional stress wave propagating through a bar.     

Material properties using holographic interferometry

A particular optical configuration has been used by the authors to holographically obtain interference patterns which are unsensitive to rigid body translations. The fringe pattern depends on the strains and any rotations of the body. When a curved surface or several flat surfaces of a homogeneous body are viewed simultaneously, rotations can be eliminated from the fringe pattern, and the strain in the viewing direction can be determined from a single view of the hologram. This technique has been used to measure the thermal expansion coefficients of a beryllium rod and the shear modulus of an aluminum bar with an accuracy of a few percent.     

Application of pulsed holographic interferometry to the measurement of propagating transverse waves in beams

The technique of double-exposure holographic interferometry was used to record transverse waves propagating in a long beam. The wave was initiated by striking the beam in the center with a ballistic pendulum. Pulsedlaser interferograms were obtained which showed the bending waves at three different times after the initiation of impact for three different experiments. From the interferograms, plots of the transverse displacement vs. distance along the beam were obtained. The experimental data compared favorably with analytical results for the problems. The experimental technique, differential interferometry, was also introduced to facilitate measurement of largeamplitude motions using holography.     

Application of holographic interferometry for evaluation of 3D Navier-Stokes calculations

Holographic interferometry is a non-intrusive optical measuring technique which can potentially capture instantaneous information about a complete three-dimensional flow field onto a single holographic image. However subsequently extracting the flow data so that it can be used to validate CFD results, is for most practical wind tunnel applications not yet possible.An approach applied in this paper, is to compare experimental interferograms with equivalent images obtained by post-processing the CFD solution. We have investigated transonic flow in a wind tunnel environment and computationally reconstructed both 2D image-plane interferograms and full 3D holographic interferograms. These comparisons have subsequently helped us to evaluate and improve our 3D Reynolds Averaged Navier-Stokes calculations.The main part of this study was conducted by the authors at Cambridge University Engineering Department where the work was funded by RAE Farnborough under contract 2029/233 XR Aero and monitored by Dr. B. Williams and Dr. P. Smith     

Near-resonant holographic interferometry of hypersonic flow

Near-Resonant Holographic Interferometry is a powerful technique which extends the established advantages of conventional holographic interferometry by allowing a species-specific number density to be determined. It has been tested in the harsh flow conditions generated in a high enthalpy facility yielding information about the shock shape on a cylindrical body and on the distribution of a trace species seeded into the flow. Received 7 April 2000 / Accepted 1 November 2000     

Application of digital phase-shift holographic interferometry to weak shock waves propagating at Mach 1.007

Digital phase-shift holographic interferometry was applied to visualize weak shock waves and related phenomena quantitatively. This method of interferometry is an improved version of double-exposure holographic interferometry using digital image processing and a phase shift method. The obtained interferograms were analyzed using the Carré method. To evaluate the applicability of the interferometry to quantitatively visualize the phenomena, density profiles behind weak spherical shock waves generated with 500 μg of silver azide were examined. The results of the numerical analysis performed with the hydrocode AUTODYN were compared with those of the experiment. The Mach number of visualized shock waves was estimated to be 1.007 ± 0.001 at the pressure transducer near the test section. At the shock fronts, the density difference between the experimental and numerical results was within 0.3%.     

Large-deformation measurements by real-time holographic interferometry

This paper describes a simple technique for desensitizing real-time holographic interferometry so that it can be more easily used in investigating large deformation of solid structures.     

Measurement of mixed-mode crack profiles by holographic interferometry

Holographic interferometry was used to study the mixed-mode fracture characteristics of mortar. The nature of crack propagation in such quasibrittle materials and the theoretical model used to interpret the experimental results indicated that a highly sensitive measurement technique was required. The gradual curvature of the propagating crack at different sections of the specimen necessitated full-field observation capability. The nature of the problem made holographic interferometry the ideal technique for this application. To measure the in-plane components of the opening and sliding of the crack surfaces during propagation, a single holographic plate was placed very close to the specimen. This allowed four independent observations of any point on the specimen from the four corners of the plate without any need for additional optics of exposures. Double-exposure holograms were made at different crack-propagation stages. The developed plate was illuminated by an unexpanded reference beam to form a real image of the object and observe displacement fringes. Fringe data were interpreted by using computer software written for this research.     

Phase step holographic interferometry applied to hypervelocity,non-equilibrium cylinder flow

For blunt bodies the reduced bow shock wave stand-off distance and the shock layer density rise in the stagnation region as compared to ideal gas flow are phenomena caused by dissociative effects. In this work experiments with aR _BODY=45 mm radius cylinder and an aspect ratio ofL/R _BODY 11 are described. The tests were carried out in the High Enthalpy Shock Tunnel in Göttingen (HEG), a free piston driven shock tunnel. Two different test conditions at reservoir enthalpies of around 21 MJ/kg and Mach numbers of around 9 in air and nitrogen were available.Optical measurements with a holographic phase step interferometer to obtain complete flow field density gradients have been carried out. By increasing the signal-to-noise ratio with the technique of phase stepping over the original recording quality, high quality interferograms are obtained. The high spatial resolution of the holograms results in the creation of hologram-schlieren images which are compared to directly recorded laser-schlieren images.Infinite and finite fringe interferograms and the complete density fields for the two free-stream conditions are presented. The stagnation line densities are quantified. The measured results are shown and compared with Navier-Stokes calculations which account for chemical reactions in the flow. The numerical code underpredicts the stand-off distance of the bow shock wave. It is shown that the flow behind the bow shock wave is in non-equilibrium and that it reaches equilibrium before the body for one condition.This work was an offshoot of an ESA research contract monitored by Dr. D. Vennemann, whose support is gratefully acknowledged. This study of stagnating high enthalpy flows has exceedingly benefited from discussions with S. Brück and V. Hannemann. The operation of the large wind tunnel HEG is the result of a team effort. The with to thank the whole team, represented by Dr. W.H. Beck, for keeping the tunnel going.     

Crack profiles in mortar measured by holographic interferometry

In order to test the accuracy of theoretical fracture models for mortar and concrete, it is necessary to have accurate measurements of the crack profiles. In this study, sandwich holographic interferometry has been used to find the crack profiles in a center-notched plate specimen loaded at the center of the notch. The results have shown that at low load levels with corresponding short crack lengths, there is little difference between the measured crack profiles and elastic crack profiles computed by finite-element analysis. At high loads with long crack lengths there is a large difference between measured and computed elastic crack profiles. The data suggest the presence of a closing pressure at the crack tip and that there may be a limit to crack-tip-opening displacement (CTOD) before the crack propagates.     

A study of effective crack length using holographic interferometry

A technique using holographic interferometry and models of thin-sheet PMMA has been adapted to study the effective crack length for slots with rounded tips of various radii. The results suggest a rational means of applying sharp-crack fracture mechanics in certain nonideal situations and are compared with earlier studies.     

Stress analysis of thin polyimide films using holographic interferometry

It is proposed that the residual stresses due to curing in a spin-coated polyimide film can be determined using the solution to the problem of a vibrating membrane. The membrane is biaxially constrained and supported on a metal washer or copper substrate. A piezoelectric transducer is used to excite the sample. The membrane vibrates uniformly in response to its resonant frequencies. The vibration pattern is recorded using time-average holographic interferometry. The pattern produced is indicative of the mode of vibration. The biaxial stress in the film can be calculated from measuring the characteristic frequency, the density of the material, and the mode of vibration. The effect of mass loading of air on the apparent stress in these membranes is also investigated. Measurements made in vacuum appear to resolve this problem. The stresses calculated are on the order of 10 MPa.