Improved residual stress evaluation with Hole-Drilling and DIC through the L-curve tool and super-resolution along depth

Full-field methods such as Electronic Speckle Pattern Interferometry (ESPI) and Digital Image Correlation (DIC) emerge as promising alternatives to strain rosette in the hole-drilling method, each with its own advantages and limitations. In particular, DIC stands out as a method requiring minimal (and cheap) specimen preparation; however, its sensitivity is approximately one order of magnitude lower than that of conventional strain gauge techniques. We address two fundamental questions. First, how can the inverse problem of the hole-drilling method be systematically approached outside the well-established framework of ASTM E837, which provides users with comprehensive guidance, including automated regularization procedures? Second, thanks to full-field measurement techniques, is it possible to retrieve stress distributions at a spatial resolution finer than the drilling step? We revisit the theoretical development of the inverse problem, aiming to directly identify the residual stresses from raw images, without intermediate pre-processing of the displacement fields. We introduce the L-curve method – well established in other scientific domains – as a rational tool for the choice of the regularization parameter. Finally, we show that, in principle, it would be possible to identify the entire stress distribution from a single drilling increment. We perform a deep rolling treatment on an aluminum specimen and compare the residual stresses identified using both a strain gauge rosette and DIC. We demonstrate that the proposed framework yields results comparable to those obtained using strain gauge rosettes, while minimizing user-dependent arbitrariness. Furthermore, we show that depth superresolution of at least a factor of two is already achievable with current technological capabilities.