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Near-infrared laser surface treatment of milled CFRP aircraft structures for bonded repair applications
Citation Link: https://doi.org/10.15480/882.3091
Publikationstyp
Doctoral Thesis
Date Issued
2020
Sprache
English
Author(s)
Advisor
Referee
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2020-10-02
TORE-DOI
TORE-URI
First published in
Number in series
38
Citation
Technisch-wissenschaftliche Schriftenreihe / TUHH Polymer Composites 38 (2020)
Carbon fibre reinforced polymers (CFRP) are widely used as a material for aircraft structures. During their lifetime, aircraft structures can be subject to damages that have to be repaired to maintain aircraft safety. For a lightweight and material-efficient repair, the scarf bonded joint is the preferred solution. The scarf bonded joint is produced by removing the damaged material by milling and the application of a repair patch through adhesive bonding. A critical step during the adhesive bonding process is surface treatment since it significantly influences the bond strength.
This work investigates the effects of near-infrared (N-IR) surface treatment on the adhesive properties of milled CFRP. The laser treatment is able to remove disruptive milling debris from the surface. As a result, a significant increase in bond strength is achieved. Furthermore, the laser treatment is able to strip the fibres. The fibre stripping improves the bond strength compared to the already high standard of the reference process. The increase of the roughness and surface area is seen as the driving mechanism behind the further improvement. Opposed to the reference process, laser treatment is additionally capable of removing contaminations. The removal of contaminations is a considerable advantage of laser treatment, given the severe risk that is posed by contaminations. Though no clear evidence of a functionalisation was found, the chemical composition shows a high functionality without any contaminations and is therefore suitable for adhesive bonding. The main downside of the process is the physically induced interaction between the epoxy resin matrix and the N-IR laser and the consequential formation of cavities under matrix-rich areas. The cavities, though comparably small, can only be partially filled and could induce failure in the bond.
Nevertheless, for all tested scarf ratios and lay-ups, an increase of the bond strength compared to the reference process was achieved. This shows the high potential of N-IR laser treatment for composite repair applications.
This work investigates the effects of near-infrared (N-IR) surface treatment on the adhesive properties of milled CFRP. The laser treatment is able to remove disruptive milling debris from the surface. As a result, a significant increase in bond strength is achieved. Furthermore, the laser treatment is able to strip the fibres. The fibre stripping improves the bond strength compared to the already high standard of the reference process. The increase of the roughness and surface area is seen as the driving mechanism behind the further improvement. Opposed to the reference process, laser treatment is additionally capable of removing contaminations. The removal of contaminations is a considerable advantage of laser treatment, given the severe risk that is posed by contaminations. Though no clear evidence of a functionalisation was found, the chemical composition shows a high functionality without any contaminations and is therefore suitable for adhesive bonding. The main downside of the process is the physically induced interaction between the epoxy resin matrix and the N-IR laser and the consequential formation of cavities under matrix-rich areas. The cavities, though comparably small, can only be partially filled and could induce failure in the bond.
Nevertheless, for all tested scarf ratios and lay-ups, an increase of the bond strength compared to the reference process was achieved. This shows the high potential of N-IR laser treatment for composite repair applications.
Subjects
CFRP
repair
surface treatment
laser treatment
scarf bond
bonded joints
Aerospace
epoxy
adhesive bond
DDC Class
600: Technik
620: Ingenieurwissenschaften
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Name
Dissertation_Sergej-Harder.pdf
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4.16 MB
Format
Adobe PDF