Residual stress by blind-hole method with off-center hole

Application of the blind-hole drilling technique to measurement of residual stresses in areas too restricted for drilling guides is now possible by using a set of equations derived to account for off-center drilled holes. Prior technique required the hole to be drilled concentric with the gage center within ±0.001 in (0.0254 mm), thus requiring the use of a precision locating and drilling guide. The equations apply to commercially available 0-, 90- and 225-deg strain-gage rosettes, but can be easily modified or scaled for different arrays. Details of a hand-drilling procedure are presented, along with examples. Potential errors and data interpretation are discussed.