Three-dimensional recovery of stress intensity factors and energy release rates from surface full-field displacements

The identification of stress intensity factors (SIFs) from full-field displacement measurements by the optic method is accelerating rapidly following the development of precise digital cameras and image correlation algorithms. Nevertheless, as only surface displacements are available, most of the identification methods used up to now have been restricted to problems that are invariant with respect to the normal direction of the free surface and must rely on the plane elasticity hypothesis. The problem of SIFs identification is tackled here in a full three-dimensional framework by first deriving a data completion method in elasticity to determine the elastic displacement field inside the solid on the basis of surface displacements. The method solves the Cauchy problem for the Lamé operator after which usual numerical methods for computing SIFs and energy release rates can be used. Numerical applications in three-dimensional elasticity are described first for a cracked specimen subjected to 3D loadings and, secondly, for a heterogeneous specimen in a quasi-plane situation.