Research Information System
Thesis Type: Postgraduate
Institution Of The Thesis: Gazi University, Fen Bilimleri Enstitüsü, Turkey
Approval Date: 2023
Thesis Language: Turkish
Student: Yavuz AKALIN
Supervisor: Derya Özgür
Open Archive Collection: AVESIS Open Access Collection
Abstract:
During production of air vehicles, the assembly of composite and metallic parts, adhesives and bonding agents are utilized as alternative or complementary methods. While the overall strength of structures produced using adhesive bonding is contingent on various factors, different manufacturing techniques for composite parts emerge as prominent determinants. In particular, the different curing processes employed can significantly impact the structural integrity of the composite parts. For adhesive bonding of composite materials, there are three main processes: simultaneous curing (co curing), simultaneous bonding (co-bonding), and secondary bonding. In this research, the joining of carbon fiber reinforced epoxy composite materials was investigated through three different bonding techniques for composite-composite configurations, as well as for composite-steel-composite configurations. Test panel productions were carried out in a clean room, and the polymerization process was completed in an autoclave. The created test panels were compared based on critical parameters such as single-lap shear strength, interlaminar shear strength, and glass transition temperatures. Test panels with composite-composite configurations bonded using the secondary bonding technique exhibited the highest adhesive strength (25,97 MPa) in terms of single-lap tensile strength with respect to co-bonded (25,97 MPa) and co-cured (21,03 MPa) technique. Among the test panels with composite-steel-composite configurations, those bonded using the co- curing method (25,26 MPa) exhibited the highest adhesive strength with respect to secondary bond (21,52 MPa) and co-bond (20,69 MPa) technique. As a result of interlaminar shear strength tests composite-steel composite configuration revealed 75,84 MPa, composite-composite configurations revealed 75,84 MPa strength values and the difference among these results (%3,5) is not a considerable fluctuation. This is due to the failure mode occurring between the composite layers. According to DMA test results, glass transition temperature of adhesive system (FM300K) in co-cured test panels (154,21°C), is 14°C higher than the co-bonding and secondary bonding techniques (139,93°C) which is due to co-cured test panels has 11 minutes longer polymerization time with respect to two other bonding techniques. Considering the evaluations performed, it was determined that changes in the curing time and temperature of the epoxy resin had a greater impact on glass transition temperature measurements than the bonding method or surface preparation techniques. The findings indicate that process optimization for joining carbon fiber composites with steel cannot be achieved by simply changing the bonding method. Therefore, optimizing the process, including determining the most suitable methods for part production and assembly, is evaluates as a strategic decision that requires considering all relevant factors (surface preparation, part geometry, curing processes, thermal expansion coefficients, etc.) during the production stage.
Key Words : Carbon-epoxy composite, steel, co-curing, co-bonding, secondary
bonding, adhesion process