Displacement measurements around cracks in three-dimensional problems by a hybrid experimental technique

Diffraction gratings were applied to slices taken from three-dimensional stress-frozen models of bodies with cracks. The slices were then annealed to relax the reversible strains and moire interferometry was used to determine the deformation of the slice. A virtual reference grating of 1200 l/mm (30,000 l/in.) was used to provide the required high sensitivity. The moire pattern in the LEFM (linear-elastic fracture-mechanics) zone was photographed with 20 × magnification. Results were compared with those obtained photoelastically.