Editing Moiré pattern (section)

=== Strain measurement ===
{{See also|Theory of elasticity|Strain tensor|Holographic interferometry}}
[[File:Moire extensometrie.png|thumb|Use of the moiré effect in strain measurement: case of uniaxial traction (top) and of pure shear (bottom); the lines of the patterns are initially horizontal in both cases]]

In [[manufacturing]] industries, these patterns are used for studying microscopic [[Strain (materials science)|strain]] in materials: by deforming a grid with respect to a reference grid and measuring the moiré pattern, the stress levels and patterns can be deduced. This technique is attractive because the scale of the moiré pattern is much larger than the deflection that causes it, making measurement easier.

The moiré effect can be used in [[Strain (materials science)|strain]] measurement: the operator just has to draw a pattern on the object, and superimpose the reference pattern to the [[Deformation (engineering)|deformed]] pattern on the deformed object.

A similar effect can be obtained by the superposition of a [[Hologram|holographic]] image of the object to the object itself: the hologram is the reference step, and the difference with the object are the deformations, which appear as pale and dark lines.