Surface and internal strain fields near coldworked holes obtained by a multiple embedded-grid moire method 

 -  Engineering Fracture Mechanics, 19(2), p.375-381, 1984 .
<br/><br/> Surface and internal radial, hoop, and transverse strains created by tapered mandrel were measured. Multi-layer polycarbonate specimens with surface and embedded gratings were studied using moire methods. The technique involved high-resolution photography of the gratings for each specimen state, optical processing of the grating replicas, and digital data reduction to create strain maps. The strains on the surfaces were not the same. The hoop and radial strains on the specimen midplane were smaller than on either surface. The compressive transverse strain is maximum at the midplane, but it has a small tensile value near the mandrel entry side. The strain fields, in general, are much more complex than existing theoretical solutions suggest.