Increasing the Maximum Measurement Depth of IHD in Thin Isotropic Plates

Abstract Background The integral computational method has been used extensively for residual stress measurement with incremental hole-drilling and makes use of a single top surface strain gauge rosette. The method is depth limited due to the loss of strain gauge sensitivity as the hole depth increases. Objective The objective of this study is to develop an experimental and computational approach to properly incorporate, into an integral solution, the data from a strain gauge rosette on the bottom surface in addition to those of the existing rosette on the top surface and hence increase the maximum achievable measurement depth. Methods Top and bottom surface strain gauge rosettes are bonded coaxially on a thin aluminium AA6082-T6 specimen and the IHD procedure is performed through the thickness of the specimen. The unit pulse integral method is applied to generate calibration coefficients for the top and bottom rosettes through FE analysis. All the strain measurements and calibration coefficients are used in a single least-squares solution to determine the through-thickness residual stress distribution. Tikhonov regularization is additionally employed to smooth the stress solution. Results The proposed approach, which combines the top and bottom rosette data, demonstrates reduced uncertainty through the full thickness of a specimen thinner than 50% of the mean rosette diameter. The maximum hole depth can be increased to 245% of that of a single rosette IHD test. Conclusions Combining the top and bottom rosette data improves the residual stress solution in a thin specimen compared to a single rosette solution through reduced uncertainty, especially in the mid-depth of the specimen, and significantly increases the achievable measurement depth.