In developing Type V hydrogen tanks for energy storage and propulsion in commercial airliners, the key design criterion is maintaining tightness under cryogenic conditions. A concern is that anomalies in the laminate could cause microcracks which compromise the tightness. This study examined how resin flow, caused by an expanding mould during curing, creates a gradient in the local fibre volume fraction (FVF) across the laminate. The impact of resin system selection, autoclave cycle parameters, mandrel material, and fibre tension on the FVF gradient was investigated. Cylindrical specimens were manufactured in a process replicating automated fibre placement (AFP), with a piezoelectric sensor measuring contact pressure at the mandrel-laminate interface during the autoclave cycle as an indicator of resin flow and FVF spread. Significant correlations were found between resin flow and all parameters except fibre tension. The resin's viscosity profile and gelation characteristics had the most substantial impact on the FVF spread. Resins with high viscosity and short gelation times lowered the FVF spreads the most. Mandrel materials with lower thermal expansion coefficients (CTE) also reduced FVF gradients, though to a lesser extent. Adjusting the autoclave cycle to lower temperatures for longer periods resulted in the least significant reduction in FVF spread; however, this approach holds high potential for further improvement if more data on resin rheology and cure kinetics are available to optimise the autoclave cycle. These findings provide valuable insights for minimising FVF gradients in the design of carbon fibre-reinforced polymer (CFRP) tanks for liquid hydrogen.

In recent years, lightweight composites have become increasingly popular in several industries for the benefits they offer such as high strength to weight ratio, cost efficiency, tailorable properties and superior mechanical performance. The performance of these lightweight composites can be further optimized by using spread tows as a reinforcement solution. Tow spreading is a process of flattening fibre tows into thinner and wider tapes with a low aerial weight which increases resin impregnation of fibres, lowers void content in impregnated tows and produces lightweight composites with improved damage tolerance.

The majority of tow spreading technology however is owned by companies in the form of intellectual property and patents thus limiting the scientific understanding of the process. This aspect leaves tow spreading open as a field of research for exploration and investigation. While some previous studies have investigated the process of tow spreading, the applicability of these studies has so far been limited in their experimental apparatus. These studies identified the gap that exists between the sophisticated industrial technology and the research setups hence providing an incentive to further develop an experimental facility that generates a deeper understanding of the current industrial practices in tow spreading.

In this research, a mechanical tow spreader was developed that utilizes cylindrical spreader bars to facilitate the spreading of fibres. This was followed by an experimental analysis where different input parameters in the tow spreader such as tension, spreader bar orientation, heat and speed among others were investigated to understand their influence on spreading behaviour. Lastly, a microstructural investigation of spread tow was conducted where a technique to capture the spread of fibres in the tow was developed and microstructural samples were generated. These samples were then observed under a microscope to visualize the evolution of fibre distribution as the tow spreads.