The paper focuses on the moire phenomenon as a tool of experimental mechanics. The properties of moire patterns are outlined. The application of these properties to the measurement of displacements of the points of a surface (intrinsic moire), contours or deflections (projection moire) and slopes (reflection moire) is discussed. Observation methods, recording methods, data-processing techniques are outlined and practical aspects are stressed. Sensitivities and precisions that have been achieved are reviewed. Finally, some typical applications to problems in areas of interest are briefly described.

The moiré method—A review

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.

A method for directly determining surface strain fields using diffraction gratings

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.

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

Gratings provide a means for the direct determination of displacement and strain fields. Gratings engraved in a model experience changes from the undeformed to the deformed condition and these changes can be utilized to determine displacements or strains. Gratings projected on a surface also experience changes when the surface is deformed. The different mechanisms of detection of the grating changes are discussed and the basic fundamentals necessary to understand the detection techniques are reviewed. The broad scope of the material presented should give the reader a good starting point to understand the present state- of-the-art developments. Although, in view of the length of the material presented in the paper, no practical applications are discussed, we must remark the fact that there is a very extensive literature of applications of gratings to the solution of problems of technical interest.

Use of gratings in strain analysis

Der Moireeffekt bietet wie keine andere physikalische Erscheinung eine kaum zu ubersehende Vielfalt von Anwendungsmoglichkeiten, wenn es darum geht, Verformungsoder Verschiebungszustande von Korpern sichtbar und analysierbar zu machen. Er ist wesentlicher Bestandteil einer sehr grosen Anzahl von Verfahren, die in den letzten beiden Jahrzehnten nicht nur auf dem Gebiet der Modellstatik, sondern ganz allgemein zur experimentellen Spannungsbestimmung entwickelt wurden. Insbesondere bei der Untersuchung plastischer Verformungen und thermischer Probleme durfte das Moireverfahren grosere Bedeutung erlangen, da die Messungen beruhrungslos erfolgen und die exakte Bestimmung auch relativ groser Dehnungen ermoglicht.

Die modellstatischen Moiréverfahren

Moiré fringe multiplication with a spatially filtering projection system

A technique is described for the preparation of contact-copy prints of gratings by means of reflex photography. The authors suggest that the method gives increased contrast and definition compared with classical methods of preparing prints.

W. Beeck

Papers

Moiré fringe multiplication with a spatially filtering projection system

Lensless photography of gratings