Analysis of Blind-Holes Applied in the Hole-Drilling Method for Residual Stress Measurements

The measurement of residual stress by the Hole-drilling method consists basically of drilling a blind-hole in the material under study. That relieves and redistributes the stresses around this hole promoting a surface deformation which adapts to a new equilibrium condition. This deformation provides, indirectly, information on the stress state to which the part or component is submitted. However, when not properly controlled, the drilling process can introduce additional stresses in the hole walls. Thus, the true value for the residual stress may be masked. Therefore, in this study, the hole-drilling process was investigated. More specifically, the influence of the feed and rotational speed on the hole walls and bottoms was evaluated. In addition, the hole geometry produced by the end-mill was investigated. Blind-holes were produced in the alloys A36 steel, AISI 304 L stainless steel and AA6061 aluminum, using an air-turbine, which provided an average rotational speed of 220,000 rpm. Only two feed rates were applied. The geometric measurement of both the tools and the holes produced showed that the hole geometry deviated from that recommended in ASTM E837-13a. Both decrements and increments in the hardness value for the hole walls and bottoms were observed, indicating that the process may have reached very high temperatures.