Experimental evaluation of atmospheric plasma treatment effects on different textures of CFRP composite for aircraft applications

Abstract

This article examines the impact of Atmospheric Plasma Treatment (APL) on the chemical composition and fracture properties of various textured surfaces (tool and bag side) of carbon fiber/epoxy (CFRP) composites utilized in aircraft applications. For this purpose, parameters of atmospheric plasma (APL) surface treatment were evaluated in comparison to chemical cleaning and peel-ply applications, taking into account its effects on surface properties and adhesive bond strength. A comprehensive variety of surface characterization techniques were utilized to analyze surface modifications, including water and diiodomethane contact angle measurements for assessing surface hydrophilicity, Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection (FTIR-ATR) and X-ray Photoelectron Spectroscopy (XPS) for analyzing chemical composition and functional groups, and Profilometry, Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM) for evaluating surface topography and morphology. Experimental results indicated that the reduction in the contact angle following plasma treatment correlated with the elevated oxygen concentration and the presence of polar functional groups (e.g. -OH, -NH₂, -NH₃, C=O, O-C=O) on the composite surface. Plasma treatment, especially at low nozzle speeds, increased surface roughness on the bag side surfaces. This prevented adhesive penetration and led to gas entrapment, resulting in adhesive failure mode and reduced single lap shear strength for the bag side. In contrast, on the tool side surfaces, the plasma treatment led to a remarkable 19.7% enhancement in shear strength, highlighting its effectiveness.

Keywords:

• Aircraft composites
• surface treatment
• atmospheric plasma
• adhesion by chemical bonding
• X-ray photoelectron spectroscopy

Nomenclature

AFM	=	Atomic Force Microscopy
APL	=	Atmospheric Plasma
ASTM	=	American Society for Testing and Materials
BS	=	Bag Side
CA	=	Contact Angle
CFRP	=	Carbon Fiber Reinforced Plastic
FTIR-ATR	=	Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance
IPA	=	Isopropyl Alcohol
LSS	=	Lap Shear Strength
OWRK	=	Owens, Wendt, Rabel, Kaelble
PP	=	Peel-Ply
PTFE	=	Polytetrafluoroethylene
SEM	=	Scanning Electron Microscopy
SFE	=	Surface Free Energy
SLJ	=	Single Lap Joint
TS	=	Tool Side
v	=	Plasma Nozzle Speed
WCA	=	Water Contact Angle
XPS	=	X-ray Photoelectron Spectroscopy

Acknowledgements

This study was supported by the Scientific and Technological Research Council of Turkey (Turkish Aerospace Industries-Yıldız Technical University 2244 – Industrial Ph.D. Fellowship Program/project number: 118C071).

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Credit author statement

Ahmetcan Alkoc: Investigation, data curation, writing-original draft.

Afife Binnaz Hazar Yoruc: Project administration, supervision, writing – review and editing.

Mete Bakir: Supervision, funding acquisition.

Adem Can Usak: Resources, validation, writing – review and editing.

Data availability statement

The data that support the findings of this study are available from the corresponding author, [A.A.], upon reasonable request.

Additional information

Funding

This work was supported by the Turkiye Bilimsel ve Teknolojik Arastirma Kurumu [118C071].