The Application of Digital Image Correlation for Measuring Residual Stress by Incremental Hole Drilling

Abstract

The measurement of residual stress using the incremental hole drilling is well established, but the main limitations with the conventional strain gauge approach are the requirements for surface preparation, the need for accurate alignment and drilling, the restricted range of hole geometries commensurate with the specific gauge designs, and the limited range of strain data averaged over the footprint of the strain gauge grid. Recent attempts to extend the method have seen the application of full field optical techniques such as electronic speckle pattern interferometry and holographic interferometry for measuring the strain fields around the hole, but these methods are sensitive to vibration and this limits their practical use to controlled laboratory environments.There are significant potential benefits therefore of using a more robust technique based on Digital Image Correlation (DIC), and work is presented in this study on the development of the method for measuring surface displacements and strain fields generated during incremental hole drilling. Some of the practical issues associated with the technique development, including the optimization of applied patterns, the development of the optical system and integration with current hole drilling equipment are discussed, and although measurements are only presented for a single load case -the equi-biaxial stress state introduced during shot peening -the novel aspect of this work is the integration of DIC measurements with incremental drilling and an application of the Integral Method analysis to measure the variation of residual stress with depth. Validation data comparing results from conventional strain gauge data and FE models is also presented.

Residual Stress Determination by Hole Drilling Combined with Optical Methods

“…DIC allowed displacements from hole drilling to be found and related to residual stresses using computational methods similar to those developed earlier for the interferometric approaches reviewed here. In 2008, Lord et al [108] extended DIC-hole drilling to enable the determination of profiles of residual stresses from shot peening vs. depth using incremental drilling, with results shown in Fig. 17, where the stress profiles found by DIChole drilling agree reasonably well those determined by [108].…”

“…In 2008, Lord et al [108] extended DIC-hole drilling to enable the determination of profiles of residual stresses from shot peening vs. depth using incremental drilling, with results shown in Fig. 17, where the stress profiles found by DIChole drilling agree reasonably well those determined by [108]. Principal stresses are denoted by s1 and s3 hole drilling with strain gages.…”

Recent progress in residual stress measurement techniques

“…Nelson et al [46,47] were the first to describe the application of DIC with hole drilling and reported results for blind-hole measurements on a shrink fit ring sample using a 3D DIC system with two Megapixel cameras. In 2008, Lord et al [47] integrated DIC measurement with incremental hole-drilling and applied integral method analysis to measure the variation of residual stress with depth (Fig.5); validation data were in good agreement with those determined by hole drilling with conventional strain gauge data and FE models verifying effectiveness and reliability, as shown in Fig.6. In 2009, Gao & Shang [48] described a new approach for directly determining the residual stress with DIC hole drilling using the deformation pattern, governed by the residual stress, to transform the image captured after the deformation of the object.…”

Relaxation Methods for Measuring Residual Stresses: Techniques and Opportunities

“…Digital Image Correlation [23,[62][63][64] is a versatile optical technique for measuring surface displacements in two or three dimensions. The 2-D technique, schematically illustrated in Fig.…”