The multiple-incremental hole drilling method for determination of measurement uncertainties of residual stress measurements using the hole drilling method

The measurement uncertainties of residual stress determinations using the incremental hole-drilling-method can actually only be assessed by repeating the measurement at equivalent measurement spots or specimens. In order to reveal statistically confirmed results from only one measurement location, a multiple-incremental hole drilling method was developed at the Fraunhofer Institute for Mechanics of Materials IWM. This strategy allows multiple strain changes to be recorded for each single measurement depth by a stepwise enlargement of the hole in lateral direction for each depth increment. To calibrate this modified strategy a FE-Model was set up allowing calculation of the strain release for each step in depth- and in lateral direction for a given stress-depth profile. The new drilling and evaluation strategy was verified through measurements on specimens with a well known stress-state and applying an established differential evaluation method. The results show that, applying the lateral incremental drilling strategy, the standard deviation of each stress reading of the stress-depth profile can be evaluated.