A Study on Carbon Fibre Damage and Defects during Textile Processing

Abstract

The thesis investigates various damages and defects that occur during the processing of Carbon Fibre tows. High-performance composite materials use carbon fibre tows in forms such as woven, braided, or filament wound preforms as reinforcement materials, which control the composite’s performance and properties. Carbon fibres are prone to damage due to their brittleness during the preform manufacturing. Factors such as tow sizing, fibre yield, surface quality of machine parts, and manufacturing parameters can influence the extent of fibre damage. During specific preforming techniques, defects are introduced to the continuity of the filaments of the carbon fibre tows. The study aims to examine the causes of tow damage and defects in the preforming stages, their impact on the final performance of the composites, and a way to grade the tows based on the damage levels. The study involved manufacturing of preforms by weaving, braiding, and filament winding to obtain samples for studying the damages and defects. Both virgin and recycled 12k carbon fibre tows were used for the manufacturing. The filament winding process was also modified by introducing fixed levels of artificial damage to the carbon fibre tows using abrasive materials to study varying levels of tow damage. A novel electrical impedance measurement method on the carbon fibre tows from all the preforming techniques was used to predict tow damage level in terms of loss of filaments in the tows. The impedance of carbon fibre tows was accurately measured, with an average deviation of 0.7% between samples. The results from the electrical impedance experiment showed which of the processing zones of preforming methods caused the highest levels of damage to the carbon fibre tows. The sizing content in the carbon fibre tows and the number of processing zones in the preforming method influenced the level of damage. This was observed in 60E 12k carbon fibre tows with a low size content used in the braiding of preforms, which had the highest loss of filaments to damage, and filament winding caused the least damage to the carbon fibre tows. To validate the effectiveness of the prediction, carbon fibre tows collected from various stages of the preform manufacturing with varying degrees of damage were infused with resin to form tow composite rods, which were then subjected to tensile loading to understand the impact of the damage and defects on the mechanical properties of the composites. Artificially damaged tows exhibited a 16% loss in tensile strength under tensile loading over the virgin carbon fibre tows. As part of studying defects, recycled carbon fibre tows were used to manufacture braided tubular composites. The composite tubes were cut into rings and tested in tensile loading to analyse the effect of recycling carbon fibre tow on the strength properties of the composite. Composites with recycled carbon fibre tows showed a 30% loss in tensile strength. Manufacturing braided tubular composites with low tension on the tows leads to defects in the form of wrinkles on the walls of the composite. The effects of the wrinkles on the composite strength were mechanically characterised under tensile loading. The presence of wrinkles caused a 44% loss in tensile strength. Splicing a pneumatic method of joining two carbon fibre tows introduces discontinuity defects to the filaments. The study investigated the impact of joining tows by splicing the composite strength by manufacturing braided and filament-wound tubular composite rings using spliced carbon fibre tows and testing them under tensile loading. Certain splicing configurations caused a 50% loss in ultimate tensile strength in the braided composite and a 20% tensile strength loss in tow composite rods. X-ray Computed Tomography was used to scan and image the wrinkle defects in the braided composite, which offered analysis of the bending and change in braid architecture due to the formation of wrinkles. The analysis from the impedance measurement experiment and the mechanical testing of the composite and carbon fibre tows with damages and defects were correlated to identify processes that lead to high levels of damage. The study concludes the effect of carbon fibre damage and defects on its processability.

Date of Award	19 Nov 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Prasad Potluri (Main Supervisor) & Anura Fernando (Co Supervisor)