Stress intensity factors are obtained from displacement-prescribed boundary conditions on a subregion containing the crack. The subregion, whose boundary can be any arbitrary contour within the physical structure, is analysed numerically using structural finite elements. Nodal boundary displacements of this subregion are obtained photomechanically using a smoothing finite element representation. The technique requires little experimental information and is unaffected by rigid body motions. It is numerically stable and accurate - even in the presence of significant experimental scatter - and the measured data need not come from the immediate vicinity of the crack. The method's practicality is demonstrated by determining the stress intensity factors in a compact tension specimen from moiré-measured displacements at locations away from the crack tip.
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