In developing Type V hydrogen tanks for energy storage in commercial airliners, the key design criterion is maintaining leak-tightness under cryogenic conditions. A concern is that anomalies in the laminate could cause microcracks, potentially compromising leak-tightness. This study investigates how resin flow, caused by mandrel expansion during curing, creates a gradient in the local fiber volume fraction (FVF) along the laminate thickness. An experimental study was performed comparing two resin systems, Hexcel 6376 and Teijin Q183. Cylindrical specimens were manufactured incorporating piezoresistive sensors to measure contact pressure at the mandrel-laminate interface during the autoclave cycle, serving as an indicator of resin flow and FVF variation. Micrographs of the specimen were taken, and a machine learning-based segmentation model was used to detect fibers and resin in the images, enabling calculation of the local FVF. The results show distinct through-the-thickness gradients in FVF for both laminates with a spread of 11.6 %pt. for Hexcel 6376 and 4.5 %pt. for Teijin Q183. These observations could be correlated to the processing characteristics of the two systems and therefore provide valuable insights for developing strategies to minimize FVF gradients in the design of carbon fiber-reinforced polymer (CFRP) tanks for liquid hydrogen. ... Read more

In-situ Automated Fiber Placement (AFP) manufacturing of thermoplastic prepreg tapes has the potential to provide a fast and cost-effective manufacturing solution for large composite structures. However, it is prone to several defects, especially gaps and overlaps. One of the primary causes for this is the tape width deformation during placement. Current literature is not enough to understand this mechanism completely and the conventionally considered tape width deformation mechanism i.e., transverse squeeze flow has been suggested to be incorrect for AFP. Therefore, the research objective was to experimentally investigate the width deformation mechanism and the influence of processing parameters for thermoplastic prepreg tapes using humm3® as the heating device. The results show that the tape width deformation takes place both in the heating and consolidation phase of the process and involves spreading of the fiber-resin mixture. Additionally, the conformable roller has an influence on the post-processed tape cross-section profile. The surface roughness and the influence of the processing parameters indicate the role of temperature distribution as the influencing factor. Therefore, these results can be used to accurately model the tape width deformation to mitigate the problem of gaps and overlaps. ... Read more