• Jardon, Zoé

Abstract

Additively manufactured (AM) components are questioned for their fatigue performance and therefore not often adopted for safety critical applications so far. The components might contain material imperfections and residual stresses due to the high temperature gradients during the printing process. Thesestresses alter the component’s structural integrity and are one of the mainsources of component deformation and cracking. The effective Structural Health Monitoring system (eSHM), developed and patented by the Vrije Universiteit Brussel (VUB), fully exploits the flexibility offered by the 3D printing process by integrating a smart continuous monitoring technology inside additively manufactured parts.The system is based on the propagation and detection of pressure changes in 3D-curved internal channels (capillaries) embedded in the fatigue critical regions of the component. It is capable of detecting the presence and finding the location of a fatigue crack. The aim of this research is to developand validate a unique and robust crack localization system by exploiting this pressure data. Knowing that the nature of the waves propagating through the capillaries is determinant for the accuracy of the crack localization system, a better physical understanding of the nature of these waves is achieved by performing an experimental and numerical study of the system. Therefore,thepropagating waves are first measured with pressure sensors and then visualized by means of Schlieren high-speed imaging techniques through the capillaries.Next, a numerical and experimentalpowder-gasjet characterizationisperformed in order to assess the influence of the Directed Energy Deposition (DED) process parameters on the print process and allow to find optimal print process parameters for the integration of the eSHM-systemin an AM-part.Finally, the research is concluded with the assessment ofthe production of a sample with integrated eSHM-system using the MillingClosed-Loop ADditive (MiCLAD) in-house developed hybrid DED machine by the Additive Manufacturing Research Lab (AM-Lab) of the VUB. It has the particularity to allow the combination of, and fast change between, additive and subtractive operations forthe production of a part. Different printing strategies are proposed and compared in terms of final geometry and internal channel roughness, known to be crucial to avoid undesired fatigue initiation and to obtain an accurate detection and localization of the fatigue crack.

Topics

• Deposition
• impedance spectroscopy
• crack
• fatigue
• directed energy deposition