Static and dynamic strain measurement on a plane surface. Three-dimensional photoelasticity

For small or large strains, using two orthogonal gratings marked upon a plane measurement base, we determine, in its plane, the rotation of the rigid solid and the algebraic values of its principal extensions. An optical setting gives the measure by optical diffraction, without contact and at a distance, within 10(-5) accuracy by introducing quasi-heterodyne detection. The holographic record permits the extension of the measurement to the whole of a plane surface. For dynamic events, the grating interrogation by a beam laser with angular coding gives not only strains for local measure base but also rigid motions. In photoelasticity, the optical slicing method is recalled ; then, we introduce a new implementation with a C.C.D. camera which quickly gives isoclinics and isochromatics, and also the isostatics for a model slice bounded by two parallel plane laser beams.