Citation:
Roger M. Groves, Stephen W. James and Ralph P. Tatam. Full surface strain measurement using shearography. Optical Diagnostics for Fluids, Solids, and Combustion, Proc. of SPIE Vol. 4448, November 2001
Abstract:
Shearography is a full-field optical technique usually used for the
determination of surface strain. Correlation of interferometric speckle patterns
recorded before and after the object deformation yields fringes sensitive to
displacement gradient, from which the surface strain can be calculated. A full
analysis of the surface strain requires the measurement of six displacement
gradient components, using three illumination directions and two directions of
applied shear. Additionally shearography may be used to measure surface slope by
correlation of interferograms obtained before and after a source displacement to
yield fringes sensitive to surface slope. Integration of the slope yields the
object shape. In this paper shearography is used to measure the six components
of displacement gradient of a gas main pipe under pressure, the surface slope of
the pipe and the shape of the pipe. The object slope and shape are used to
correct the displacement gradient measurements for variation in sensitivity
vector across the object surface and for sensitivity variations due to the
dependence of the applied shear upon the local slope of the object surface. A
coordinate transformation, incorporating the object shape information, is used
to obtain the in-plane and out-of-plane displacement gradients relative to the
local profile of the surface.
