MSc.Thesis Defense:Halil Şenol
INVESTIGATION OF MECHANICAL PROPERTIES AND ADHESIVELY BONDED JOINT PERFORMANCE IN CARBON FIBER-REINFORCED POLYMER COMPOSITES THROUGH SURFACE TREATMENTS: AN ACOUSTIC EMISSION STUDY ON FAILURE MECHANISMS AND PROGRESSION
Halil Şenol
Material Science and Nano Engineering, MSc. Thesis, 2024
Thesis Jury
Asst. Prof. Hatice Sinem Şaş Çaycı(Thesis Advisor), Prof. Mehmet Yıldız
, Assoc. Prof. Bertan Beylergil
Date & Time: 20th of December, 2024 – 1 PM
Place: FENS L056
Keywords : Acoustic Emission, Failure Analysis, Surface Treatment, Plasma Treatment
Abstract
The increasing use of carbon fiber-reinforced polymer (CFRP) composites in industries such as aerospace, marine, transportation, and energy is driven by their superior strength-to-weight ratio, corrosion resistance, and thermal stability compared to conventional materials. The performance and durability of CFRP composites are significantly influenced by the adhesion between the reinforcement and matrix. Effective adhesion performance depends on surface wetting, which is governed by surface roughness and surface free energy (SFE). However, the surface of carbon fiber typically exhibits smooth and inert characteristics, limiting its wetting capability. The application of surface treatment methods to carbon fiber can enhance both surface roughness and SFE, thereby improving wetting. However, the industrial applications of CFRP composites often require assembling and adhesively bonding is a preferred alternative compared to traditional methods of riveting and bolting. The adhesion performance, strength and durability of adhesively bonded CFRP joints are highly influenced by the above-mentioned wetting parameters, in this case for adherends. Enhancing adhesion through surface treatment methods is also effective for CFRP bonded joints. While the impact of these treatment methods on the adhesion and mechanical performance of CFRP composites and adhesively bonded structures has been explored in the literature, their influence on damage mechanisms and propagation behavior requires further investigation. This study investigates the effect of surface treatment methods on mechanical performance, damage mechanisms, and damage propagation behavior of CFRP composites and adhesively bonded structures under different loading conditions. To this end, the findings of this study are presented in two manuscripts, both included in this dissertation.
The first paper presents the effect of atmospheric pressure plasma (APA) treatment on the adhesion and mechanical performance of carbon fiber (CF)/epoxy composites. The effect of APA treatment on chemical and physical properties of carbon fiber surface is examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The mechanical performance is evaluated under tensile, mode-I, and mode-II loading conditions. Additionally, the AE technique is used to analyze the damage propagation and damage mechanisms governing within the material.
The second paper investigates the impact of various surface treatments on the fracture toughness and damage progression of adhesively bonded CF/epoxy composite joints, with applied treatment methods including mechanical abrasion (MA), APA, and peel ply (PP). The chemical and physical properties of treated adherend surfaces are analyzed using various characterization techniques. Axiom Ax-2114 adhesive is used to adhere CFRP composites. Further, mechanical performance is evaluated under mode-I and mode-II loading conditions. During the test, the AE technique is used to monitor the occurring damages in real-time providing insight on damage mechanisms, failure behavior and damage propagation.