Optimisation of the injection repair method for repairing composite structures

Abstract

Composite materials find increasing applications in aerospace, automotive, and marine sectors due to their exceptional specific strength, stiffness, corrosion resistance, design flexibility, potential for reduced part count, and dimensional stability. However, the high cost of composites and the shift towards larger integrated structural components make replacing damaged parts prohibitively expensive. Consequently, efficient and reliable repair techniques need development. Various repair methods exist for different types of composite materials, loading conditions, and damage types. No single technique is universally applicable for composite repair. Instead, each type of damage requires a specific assessment to determine the most suitable repair strategy. Doubler or bonded scarf repairs have proven to be suitable for critical structural applications involving extensive delamination and damage to the reinforcement. However, they may not be viable for minor damage or delamination-dominant cases with minimal reinforcement damage. Moreover, these methods involve costly, time-consuming, and
skill-dependent material removal and surface preparation. A promising alternative for delamination-dominant damage is the Resin Injection Repair (RIR) method. Research has shown that injecting low viscosity resin into delaminated regions effectively restores the compressive strength of repaired structures.

This research project presents an experimental study on the repair of Carbon Fibre Reinforced Polymer (CFRP) laminates subjected to low velocity impacts, alongside a numerical investigation related to these impact events. The main focus was to enhance the current methodology for resin injection repairs. Currently, this repair technique is not employed to restore the compressive strength of damaged composite structures due to certain limitations in the existing methodology and apparatuses used for such repairs. A baseline methodology and resin injection repair chamber were developed based on the existing state of the art. Through an experimental study, the baseline methodology was refined to achieve optimal repair efficiency. Additionally, a novel repair apparatus called the patch chamber was designed, aiming to industrialize the resin injection repair technique.

Numerical modelling using a meso-scale approach and a proprietary computational damage model was also employed to simulate low velocity impact events. The goal was to assess the model's ability to predict delaminated regions resulting from such impacts.

Date of Award	Jul 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Defence, Sciences & Technology Laboratory (MOD)
Supervisor	Zafer Kazancı (Supervisor) & Brian Falzon (Supervisor)