Whole-field strain determination by moiré shearing interferometry

Whole-field patterns of normal strains are produced by optical shearing. The two warped wavefronts generated in the moiré interferometric system are separately sheared to produce two interference patterns. Superposition of these yields the normal strain contours. The shearing apparatus in an adjustable air wedge located near the common focal point of a telecentric lens system. By successively interrogating gratings in three directions and applying the strain rosette equation, the normal and shear strains over the entire surface can be calculated. Excellent experimental verification was obtained.