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 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.