Image processing based detection of the fibre orientation during depth-controlled laser ablation of CFRP monitored by optical coherence tomography. (May 2021)

• Record Type: Journal Article
• Authors: Holder, Daniel; Buser, Matthias; Boley, Steffen; Weber, Rudolf; Graf, Thomas
• Is Part Of: Materials & design. Volume 203(2021)
• Publication Date: 2021-05
• Subjects: Repairing of composites -- Layer-accurate laser ablation -- Fibre orientation -- Image processing -- Optical coherence tomography; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2021.109567
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: Layer-accurate and precisely stepped removal of damaged areas is required for the repairing process of parts made of carbon fibre-reinforced plastic (CFRP) to obtain a high bonding strength of the repair plies in the rebuilding process. Conventional techniques are characterized by a high degree of manual labour and mechanical load of the processed part. Here, a novel laser-based and controlled approach for automated and layer-accurate removal of damaged areas is presented. In-line depth measurements by optical coherence tomography during nanosecond laser ablation enable depth-controlled homogeneous material removal with minimum damage <10 μm and low surface roughness in the range of 7 μm to 13 μm. The processed layer must be detected for an unknown or varying layer thickness to stop the ablation process at the interface between two layers and not somewhere within one ply. The image processing-based determination of the fibre orientation from the depth measurements allow for a reliable online detection of the processed layer with a maximum error of 4° and root mean square error of 1.1°. As a result, layer-accurate damage removal is demonstrated for a complex repairing geometry. The suitability of the automated laser-based approach as preparation for repairing is proven by cross-sections and scanning-electron-microscopy. Graphical abstract: Unlabelled Image Highlights: Holistic approach for layer-accurate removal of damaged areas in parts made from CFRP as preparation for repairing. In-line depth measurements by OCT during nanosecond laser ablation enable controlled material removal with minimum damage. Image processing-based determination of the fibre orientation allows for online detection of the processed layer. Layer-accurate damage removal is demonstrated for a complex repairing geometry. Suitability of the automated approach for damage removal as preparation for repairing is proven by cross-sections and SEM.