# A Novel Low-Cost DIC-Based Residual Stress Measurement Device
## 5 Conclusions  
This paper details the development and validation of a low-cost, novel residual stress measurement device that utilises the DIC and hole-drilling method. The measurement device is significant for both academic and industrial use-cases, offering significant benefits, such as cost and time savings when compared to a strain gauge or more complicated residual stress measurement techniques. The measurement device features two-axis actuation, where a microscope and a drill are attached on the horizontal axis. Following the application of speckle patterns and aligning the sample, the device rapidly drills the desired hole, and images using a microscope, allowing for a sequence of images to be captured for measuring residual stress at the hole position. After the device was produced, the DIC hole-drilling technique was validated via a four-point bending test, where the locked-in stresses were evaluated using strain gauges and the DIC. The results aligned closely, with a deviation of less than +/ \(-\) 30 MPa in the calculated mean stresses, validating the measurement approach. The measurement device is available at the University of Bath and further information regarding the project can be found at the following link: [[https://github.com/earabul-sudo/RES-DIC-HD](https://github.com/earabul-sudo/RES-DIC-HD)]([https://github.com/earabul-sudo/RES-DIC-HD](https://github.com/earabul-sudo/RES-DIC-HD)) (accessed on 17 July 2022).  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12147233/s1](https://www.mdpi.com/article/10.3390/app12147233/s1)]([https://www.mdpi.com/article/10.3390/app12147233/s1](https://www.mdpi.com/article/10.3390/app12147233/s1)), Supplementary material includes: Assembly drawings detailing the measurement device. Manual describing the operation of the device. The g-code script and the milling parameters used for conducting the DIC experiments. The calibration coefficients, \(\underline{q}\) and \(\underline{b}\), for calculating the residual stresses using the DIC and strain-gauge hole-drilling methods. Speckle pattern images for points C and T showing the evolution of the speckle patterns during drilling. Every fifth image is provided due to file size restrictions.  
**Author Contributions:** Conceptualization, A.J.G.L.; Data curation, E.A.; Investigation, E.A. and A.J.G.L.; Methodology, E.A.; Software, E.A.; Supervision, A.J.G.L.; Validation, E.A.; Writing--original draft, E.A.; Writing--review & editing, A.J.G.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data regarding the design and production of presented device are openly available in [[https://github.com/earabul-sudo/RES-DIC-HD](https://github.com/earabul-sudo/RES-DIC-HD)]([https://github.com/earabul-sudo/RES-DIC-HD](https://github.com/earabul-sudo/RES-DIC-HD)) (accessed on 17 July 2022). The experimental data presented in this study are available in Supplementary Materials.  
**Conflicts of Interest:** The authors declare no conflict of interest.