MSc.Thesis Defense:Buse Ataç

ENHANCING THE QUALITY OF RESISTANCE WELDING OF CF/PEKK COMPOSITES UNDER ROOM- AND LOW-TEMPERATURE CONDITIONS: THE ROLE OF WELDING TIME AND DOUBLE WELDING

Buse ATAÇ
Materials Science and Nano Engineering, MSc. Thesis, 2014

Thesis Jury

Assoc. Prof. Hatice Sinem Şaş Çaycı (Thesis Advisor), Prof. Mehmet Yıldız,  

Assoc. Prof..Hasan Ulus

Date & Time: December 18th, 2014 – 13.00

Place: SU-IMC (KTMM) – Conference Hall

Zoom link:  https://sabanciuniv.zoom.us/j/6938110217?omn=97165468196

Keywords :  Thermoplastic Composites, Resistance Welding, Hot Press Process, Double Welding, Welding Time

Abstract

Thermoplastic composites are widely used in the aerospace industry due to their high strength, stiffness, durability, and resistance to harsh conditions. Their ability to be easily joined through re-melting makes them suitable for advanced engineering applications. This thesis investigates the effect of welding time and double welding on the quality and performance of resistance-welded CF/PEKK composites under both room- and low-temperature conditions.

In the study, a multi-layered heating element is used as an interlayer in the welding process of CF/PEKK laminates produced by hot press consolidation. The thermal properties of both the composites and heating elements are analyzed using various techniques. Based on these analyses, an adequate process window for resistance welding is developed to provide strong joint bonding.

Resistance welding is performed within this process window using varying welding times and the double-welding method. The performance of the welded samples is evaluated using optical microscopy, Micro X‐ray computed tomography (Micro-CT), DSC analysis, Single-Lap Shear Test (SLS), and visual inspection. The findings reveal that increasing welding time improves thermal and mechanical properties, with enhanced interface bonding. While double welding enhances the thermal and mechanical performance of samples welded at shorter durations, its application at longer welding times leads to thermal degradation, causing a slight decrease in overall performance at room temperature.

This research highlights the importance of welding time and the double-welding technique in achieving high-quality, reliable welded joints. Despite facing operational challenges, such as maintaining consistent power levels and managing defects in the heating element, the impact of welding time and the double-welding method is successfully validated and thoroughly presented. The welding process is carried out using an industrial-scale setup, ensuring that the results both validate the effect of welding time during process and demonstrate the practical applicability of the double-welding technique in resistance welding. These findings offer valuable insights for the welding operations of advanced thermoplastic composites in aerospace structural joint applications.