Residual stress characterization during laser-based Directed Energy Deposition using in-situ digital image correlation based on specular light reflection on as-built surfaces of thin walls

Abstract

Residual stresses present one of the major challenges within additive manufacturing as they lead to part distortion and cracking, production issues, scrapped parts and mechanically underperforming components. The current work presents a method to determine full-field residual stress information by deploying in-situ Digital Image Correlation during the Directed Energy Deposition process of thin walls. In an attempt not to disturb the process to apply the typical ‘speckle pattern’, the correlation analysis is based on the specular light reflection of active lighting on the as-built surface of thin walls under construction. This approach allows the continuous monitoring of the thermally induced stresses, both during the actual deposition process as well as during the subsequent cooldown phase. The method presents significant time-savings while providing maximized insight in the formation process of residual stresses. The manuscript presents the used test configuration, initial proof-of-concept results along with an accuracy estimation of the used method.