In this work, the effect of surface preparation on the damage and fracture behavior of carbon fiber-reinforced polymer (CFRP) and titanium (Ti) tubular adhesive lap-joints (TLJs) at elevated temperature (ET) is investigated. The surface physicochemical properties of CFRP are analyzed for three different surface preparation techniques: (1) as-received, (2) air atmospheric pressure plasma treatment (APPT), and (3) peel ply. To understand the effect of the surface preparation on the failure mechanisms of the TLJ, water contact angle (WCA) is employed to analyze the solid surface energy and the wetting of the adhesive on the CFRP, an optical profilometer is used to understand the surface morphology of the CFRP, and x-ray photoelectron spectroscopy (XPS) is applied to characterize the composite surface chemistry, including the identification of polar chemical functional groups that are produced from air APPT, as well as contaminants that impede adhesive bonding. From these surface characterization techniques, a relationship is built between the CFRP surface preparation and the failure mechanisms of the TLJ at elevated temperatures.The surface characterization results show that the CFRP tubes prepared with peel ply have a WCA of approximately 87⁰, compared to 20⁰ for the CFRP tubes prepared with air APPT. As a result,&nbsp;surfaces prepared with peel ply have lower surface energy and poor wetting capabilities. The optical profilometer measurements show that the CFRP tubes prepared with peel ply produce a significantly higher surface roughness than the tubes prepared with air APPT, validating the poor wetting performance. However, various scratches are observed on the CFRP tubes prepared with air APPT, resulting in high roughness regions. In addition, the XPS measurements reveal different polar chemical functional groups that form on the surface after air APPT, unlike the surface of the CFRP prepared with peel ply. The formation of polar functional chemical groups enhances the surface's free energy and combines with adhesive molecules through hydrogen and covalent bonding.The experimental tests show better performance in tension&nbsp;when the surface of the CFRP is prepared with peel ply, where the failure mechanism&nbsp;is predominantly delamination. However, when the CFRP is prepared with air APPT, the failure mechanism is primarily adhesion failure, revealing poor interfacial strength, similar to the as-received tubes with no surface preparation. The better performance of the TLJs using&nbsp;CFRP prepared with peel ply is due to the strong interfacial strength resulting from&nbsp;the surface roughness and chemical bonds, whereas the interfacial strength of the CFRP prepared with air APPT depends&nbsp;only on the chemical bonding between the CFRP and&nbsp;the&nbsp;adhesive. From this study, the joint strength and failure mechanisms&nbsp;are expressed as a function of WCA, surface roughness, and concentration of polar functional groups.

Effect of Surface Preparation on the Damage and Fracture Behavior of Carbon Fiber-Reinforced Polymer and Titanium Tubular Adhesive Lap-Joints at Elevated Temperatures

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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