Pierre Michel Boone

Application of digital phase-shift shadow Moiré to micro deformation measurements of curved surfaces

The shortcomings of conventional shadow Moire topography have in the past been improved by means of the phase-shift method which enhances the sensitivity and allows to process the fringe patterns automatically. This paper presents a digital implementation of the phase-shifting process, which requires only one image to be taken. The grating lines, projected onto the deformed object surface, are captured directly with a digital camera. Next the reference grating is superimposed numerically onto the projected grating lines. Then a number of phase-shifts are performed taking into account the non-linearities in the expression for the height-dependent intensity field. Experimental results prove that these non-linearities can considerably affect the micro deformation measurements of curved surfaces. The proposed method is very efficient and eliminates all causes of erroneous measurements due to the miscalibration of phase-stepping devices.

Determination of slope and strain contours by double-exposure shearing interferometry

An interferometric technique is used to determine directly patterns of derivatives of displacements. In the case of plate models, the fringes are loci of equal slope; for specimens provided with surface gratings, one forms patterns of partial derivatives of in-plane displacements. A theory for the interpretation of the interference fringes in terms of displacements is outlined; some experimental applications illustrate the paper.

A method for directly determining surface strain fields using diffraction gratings: Method proposed by author is based on a spatial filtering process carried out on the diffraction pattern generated by a grating applied to the specimen surface

This paper describes a new method for determining the strain distribution at the surface of solid bodies. The method is purely optical; it uses the diffraction phenomena generated by a copy of a grating that is applied to the specimen. A suitable mask performs filtering of the diffraction pattern; the image that is reconstructed from this filtered pattern shows light and dark areas; it is shown that the boundary line of those areas is the locus of points exhibiting the same value of strain, measured along a certain direction.The magnitude of the strain can be easily calculated; it can be adjusted by a simple translation of the filter. A theoretical description of the system and some experimental results are presented.

One-step technique for enlarging straddling holographic images by white-light projection onto a diffractive screen

We demonstrate a simple holographic technique that permits enlargement of the holographic image at the reconstruction stage. The technique employs a spherical mirror to generate an image that straddles the hologram to produce the maximum depth. The holographic image is projected with a white-light reconstruction beam, a lens, and a transmission diffractive screen to an enlargement of up to 5× linear magnification. Wavelength encoding of views is a new process that projects the holographic image by using all the visible spectrum and low-f -number lenses and allows for 18 simultaneous observers.

Some Problems Associated with Processing Agfa-Gevaert 8E75HD Sheet Film for Reflection Holography.

The holographic material Agfa 8E75HD sheet film is used in a Denisyuk-like type recording set-up, in conjunction with a pulsed ruby laser. A relatively simple production method is outlined, attention being given to some practical problems : sensitivity, processing, polarisation and color.

Interferometric characterization of stress birefringence in germanium

We report on the characterization of the refractive index homogeneity in large blanks of Czochralski-grown Germanium, for thermal imaging use. With a phase-measuring Twyman-Green interferometer working at 10.6 micrometers , a map of the index of refraction with an accuracy better than 1 10-5 can be obtained for blanks which do not exhibit high birefringence.In the other case, principal stresses in the disks can be determined through the effect of birefringence on the interferogram, if the stresses are distributed cylinder-symmetrically in the plane of the disk. Relations between stresses, transmittance, and electrical resistivity of the material are observed.

Coherent-optical localization and assessment of importance of damage and defects of cultural heritage

Abstract Some experimental results are presented, related to practical applications of a holographic nondestructive technique for inspection of museum item conditions, especially in the detection of deformation, stress concentration and defect localization. These results are obtained using the basic principles of traditional double-exposure holographic interferometry, as well as its electronic variant with computer image processing. In the latter case the accuracy in displacement measurements was studied on a test object. Two museum items have been selected for their condition inspection: a XVIIIth century icon on wooden panel and a precolumbian terracotta anthropomorphic. The technique described can give quite accurate metrological information, and is also rather promising for rapid qualitative analysis of the object condition before and after restoration, as well as during its storage.

Holographic investigation of brittle crack propagation in plastic pipes

Abstract Plastic pipes dominated the low pressure gas distribution piping market during the last decade. Research on steel pipes has long since indicated that the susceptibility to rapid crack propagation (RCP) increases with increasing diameter. Although most plastic pipes used in gas distribution systems are of small diameter (

Some applications of a HOE-based desensitized interferometer in materials research

A holographic method suited for the measurement of flatness deviation is presented. This method takes advantage of the basic Fizeau arrangement usually meant for contouring analysis of relatively flat bodies. A desensitized interferometer is described allowing the measurement of rough objects, as frequently encountered in engineering practice. The key component of this interferometer is a diffractive optical element produced by recording two-wave interference patterns. Desensitization factors ranging from 1 to 100 with respect to a Fizeau interferometer can be achieved. Flatness checks of computer disks demonstrate the possibilities of the interferometer; deformation measurements performed with the desensitized interferometer on classical experimental mechanics specimens are presented: static testing on notched C-rings and on welds, and fatigue testing on notched three-point bend tests.

Relative and Absolute Coordinates Measurement by Phase-Stepping Laser Interferometry

Relative and absolute coordinates measurements of real objects by phase-stepping laser interferometry are presented. The method proposed is suitable for remote nondestructive testing and accurate measurement of real object such as machine’s parts, modules, constructions, as well as archaeological monuments and in biomedical investigations for spinal deformations measurements of human body, etc. Theoretical analysis for calculation of the coordinates from the measured phase difference in illumination of the objects with different phase-shifted interference patterns as well as uncertainty of the measurements are proposed. A good agreement with experimentally obtained results is achieved.