**2.6. Residual stress analysis**

The distribution of residual stresses in the vicinity of the welding seam was measured by the hole drilling method (HDM) combined with electronic speckle pattern interferometry (ESPI) using a PRISM system, American Stress Technologies Inc. The procedure for residual stress measurement using the HDM is described in ASTM E837 standard [11]. More details about the PRISM system and the theoretical aspects can be found elsewhere [12–14].

All measurements were performed using a high‐speed air turbine at rotational speeds of 30,000 rpm, 0.04 mm/s feed rate, using a two‐fluted end mill of 0.6 mm diameter. The incremental HDM technique, which involves drilling in a series of small steps in depth, was used in the present work. The holes were drilled to a 0.3 mm depth in 10 steps of 0.03 mm. The geometry of welded plates for HDM measurements and locations of the drilled holes are presented schematically in **Figure 1**. The distance between neighbouring points was provided to be at least 3 mm in accordance with ASTM E‐837. The distribution of residual stresses across the welding region, that is, along the *Y* axis in **Figure 1**, was measured by drilling the holes at a number of distances from the weld centreline. At least three points represent each distance in the *Y* direction.

**Figure 1.** Geometry of welded plates and locations of drilled holes for residual stress measurements.
