Experimental Study about Manufacturing Parameters of Cryogenic Tank Structures Designed for Minimal Permeation

Abstract

Automated Fibre Placement (AFP) is an industrially established method for reliable automated production of carbon fibre-reinforced polymer (CFRP) with the highest quality requirements. Therefore, it has the potential to be the manufacturing method of choice for series production of full CFRP type V pressure vessels in aviation when hydrogen becomes the primary fuel source on board. The effects of technology-specific potential defects, namely gaps and overlaps, are under active investigation, mainly regarding adverse influence on mechanical properties of AFPmanufactured components. However, experimental results on the detrimental effects of these anomalies on permeation and leakage are sparse, largely owing to both AFP and type V tanks being recent technological developments. A thorough understanding of these interactions is of crucial significance for cryogenic tanks, which are exposed to large temperature fluctuations throughout their operational lifetime. Available experimental data links severe thermal cycling to the onset of microcracks, their subsequent accumulation with increased loss of propellant because of leakage, and potential failure of the laminate. This study aims to address one of the missing links in experimental results on the behaviour of AFP-specific anomalies in cryogenic conditions, with particular emphasis on their adverse effects on the rates of permeation and leakage from a type V pressure vessel. The experimental results highlight how, with current materials and due to both design anomalies (triangular gaps) and manufacturing defects (gaps and overlaps), the current state-of-the-art is yet unable to guarantee the absence of microcracks within the CFRP laminate, thus making leakage still the most relevant issue for the investigated applications. This research gap will need to be addressed with further tests to gain a full understanding of the complex interactions involved in microcracking phenomena.