**13. Conclusions**

The paper describes some improvements in the hole-drilling test method for the analysis of residual stresses, developed to increase accuracy. These improvements have been introduced to overcome some limitations and correct some errors that can derive from the direct application of the ASTM E837-13a standard.

To make calculation of the distribution of non-uniform stresses more accurate, the evaluation of residual stresses was carried out by applying the general method, based on the influence functions, proposed by Beghini et al. [8, 9]. This approach is more extensive with respect to the integral method proposed by Schajer [13, 14] and can include a dependency on a higher number of parameters. This more general approach avoids some errors and removes some limitations in the evaluation of non-uniform residual stresses deriving from the application of the ASTM E837-13a standard, which is based on the Integral method. Ultimately, the Integral method can be considered as a special case of the influence function method in which piecewise constant functions are used as the basis.

With this approach, some limitations of the standard can be overcome and, in particular, applicability of the hole-drilling test method is extended:


Furthermore, with this approach it will be possible to correct errors due to:


The paper also describes developments in measurement instrumentation with the use of automatic systems instead of manual systems and a procedure for evaluating measurement uncertainties in the case of non-uniform distribution, based on the GUM method.

*Recent Advancements in the Hole-Drilling Strain-Gage Method for Determining Residual Stresses DOI: http://dx.doi.org/10.5772/intechopen.90392*

All the features reported above have been introduced in dedicated software for the evaluation of residual stresses and related uncertainty. Finally an experimental test, performed on a 4-point bending test rig, is described.
