Measurement of Residual Stresses by the Hole-Drilling Strain Gage Method

Determining Coefficients and Introduction Whether the residual stress analysis application involves through-hole or blind-hole drilling, the coefficients and (or and ) must be determined to calculate the stresses from the relieved strains. In the case of the through hole, reasonably accurate values of the coefficients can be obtained for any particular case by analytical means, if desired. This is done by integrating, over the area of the gage grid, the component of strain parallel to the primary strain-sensing axis of the gage. Given the details of the grid geometry (line width and spacing, number of lines, etc.), slightly greater accuracy may be obtained by integrating along the individual grid lines. This method cannot be applied to blind-hole analysis because closed-form expressions relating the relieved strains to the residual stress, in terms of hole depth, are not available.

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