Effect of the Hole-bottom Fillet Radius on the Residual Stress Analysis by the Hole Drilling Method

The hole drilling method is based on the measuring of the surface relaxed strains when a small hole is drilled on the examined component. From the relaxed strains, measured generally by using special strain gage rosette, the residual stresses is computed by using proper influence coefficients, provided also by the ASTM E837-08 standard. Such influence coefficients are obtained by numerical simulations carried out by considering a centered hole with an “ideal” flat bottom. Unfortunately, in all the drilling techniques used in the practical application of the method the hole bottom is never flat and a significant fillet radius that influence the relaxed strains and then the computed residual stress, is observed. In order to detect the effect of such drawback on the computed residual stress as well to implement an accurate correction procedure, in the present work after a systematic numerical analysis performed by using the boundary element method, closed form expressions between the hole bottom filled radius and the measured strain are obtained.