The hole-drilling method allows accurate experimental stress analyses at moderate costs.
It consists in drilling a small hole(typically 1.8 – 2.0 mm) at very high speed to induce an alteration in the stress state involving a change and a redistribution of forces within the structure. This change can be measured by a strain gauge rosette with three branches, acquiring and elaborating the data to obtain the measurement of the residual stress.
The hole-drilling strain-gage method has been standardized at a world level by the ASTM E 837-13 “Standard Test Method for Determining Residual Stresses by the Hole-Drilling Strain-Gage Method”.
The ASTM E837-13 specifies the number of drilling increments required, the numerical coefficients for determining the value of residual stresses, the data processing method, the measurement-related uncertainty.
The complete hole drilling method test is made up by the following procedure:
- Installation of a three radial grid strain gauge rosette.
- Drilling of a small hole through the center of the rosette.
- Measurement of strains produced by relaxation of the residual stresses.
- Calculation of residual stresses from the strain measurements.
In terms of cost, accuracy and versatility, this is one of the more efficient non-destructive mode of relief of residual stresses. Due to this process it is also called the “method of the hole”.