The holographic-hole drilling method for residual stress determination

Holographic-hole drilling is a method developed for the rapid determination of residual stresses from an optical interference fringe pattern. A small diameter blind hole is drilled into a part containing residual stresses, and the displacements caused by localized stress relief are registered by real-time holographic interferometry. The resulting fringe pattern is evaluated to calculate residual stresses, using a simple ‘fringe counting’ method described here. Results of applying the method in laboratory tests to a variety of uniform biaxial states-of-stress from equibiaxial compression to pure shear are shown. Two sample applications of the method, the evaluation of residual stresses at a cold-worked hole and at a weld bead, are also given. Extensions of the method to evaluate stresses non-uniform in depth and/or along the surface are discussed.