ABSTRACT
Grating diffraction techniques are a special class of moiré/grating techniques. They directly measure strain, i.e. the strain is obtained without differentiation of the displacement field. The strain measurement is independent of the rigid body motion of the grating. The grating diffraction method uses only the specimen grating with no master grating. The basic principle of measurement is illustrated in figure 11.6.1. A diffraction grating bonded to the surface of the specimen follows the deformation of the underlying specimen. Consider a thin monochromatic collimated beam that is normal to the line-grating plane and illuminating a point on the specimen grating. The diffraction is governed by the equation () P sin θ n = n λ n = 0 , ± 1 , ± 2 , …. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429142765/bd523e32-3998-41a2-8515-f7d9c197908c/content/eq246.tif"/>
