Practical Experiences in Hole Drilling Measurements of Residual Stresses

Strain gauge hole drilling is one of the most widely used destructive methods for measuring residual stresses. This paper describes hole drilling from 1987 to the present day at Stresscraft. Early procedures consisted of simple installations at readily accessible sites. In subsequent years, demands increased for hole drilling on more diverse component shapes and materials. Critical details of the methodology required for credible and reliable measurements are identified and discussed. These include strain measurements, the hole forming process and strain-to-stress calculation procedures. Developments were made to improve the reproducibility and reliability of the method and accessibility at difficult target sites. Significant developments have included implementation of the Integral Method in 1989 (after G. S. Schajer) and the introduction of PC-controlled miniature 3-axis drilling machines for orbital drilling in 1999. Two machines have been used over a 10-year period to drill approximately 15,000 gauges. While the fundamental elements of the method remain unchanged, in extreme cases, gauges can now be installed and drilled at sites that can only be viewed using miniature cameras. A number of examples of installations and results are presented and discussed to demonstrate the development of the method.