Evaluation and performance analysis of composite pi-joints for structural applications

Abstract

This thesis investigates and evaluates four types of carbon composite pi-joints for use in structural applications. Two of the four types are designed and manufactured in the thesis using Automated Fibre Placement (AFP) machines and are referred to as L-style and LU-style due to their shape. The other two types are off-the-shelves components, a 3D woven pi-joint from Bally Ribbon Mills, and a braided pi-joint from A&P technology. These configurations are compared based on cost, manufacturing complexity, as well as their predicted strengths calculated using Finite Element (FE) models. These models are developed as part of the thesis to predict the behaviour and failure of the different pi-joints under pull-off and shear load cases. Additionally, three Non-Destructive Inspections (NDI) methods (X-ray CT-scan, pulse-echo ultrasonic testing (UT) and thermography) are evaluated based on their effectiveness in detecting different types of defects in pi-joints and their scalability for a future production line of aircrafts. Lastly, all manufacturing processes used for AFP, hot draping and Vacuum Assisted Resin Transfer Moulding (VARTM) are detailed along with a discussion on the challenges encountered. The results show the differences in cost, manufacturability, predicted strengths and the effectiveness of the different NDI methods.