An electronic speckle pattern interferometer for two-dimensional strain measurement

We describe an electronic speckle pattern interferometer devised to measure orthogonal in-plane strain components simultaneously and automatically. The interferometer is based on an earlier system that measured two in-plane displacement components simultaneously. Automatic displacement analysis is achieved using a phase-stepping technique. The surface strain is then calculated by numerical differentiation of the displacement data. Simultaneous measurement of the two displacement components is important for shear strain measurement because data from the two in-plane views must be combined. Results are presented for a cantilever loaded at its free end.