MEASURING RESIDUAL-STRESSES BY HOLE-DRILLING AND COHERENT OPTICS TECHNIQUES - A NUMERICAL CALIBRATION

Hole-drilling is a widely accepted method for determining residual stresses from the relaxation data obtained by a strain-gage rosette. Several researchers have recently investigated the alternative of employing interferometric techniques to reveal the displacement field produced by hole-drilling. As in the case of the standardized hole-drilling strain-gage method, proper calibration constants must be assessed so that this procedure can be effectively employed. This paper reports the displacement calibration constants derived from the results of an extensive numerical analysis. The constants proposed enable a uniform residual stress field to be determined, whatever the displacement component detected. The most commonly employed coherent optics techniques have been considered; computer-generated fringe patterns are reported and criteria are suggested to derive the stress field from fringe readings taken around the edge of the hole.