Investigation of fiber volume fraction as key parameter in cryogenic hydrogen tank development

Abstract

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.