HyTank

Test and simulation-based analysis of bonded joints for cryogenic applications and sustainability considerations for the joining process of a CFRP LH2 tank for commercial aviation

Project logo.

In order to be successful on the market in the long term, the German aviation industry must respond to the increasing demand for CO₂-emission-free flying. Cryogenic hydrogen as a fuel in combination with a turbine or fuel cell-powered engine is a promising solution. In addition to research into new propulsion systems, intensive research must also be carried out into tank systems for liquid hydrogen, as mass-optimised storage is a key element in the implementation of emission-free flight.
The main objective of the HYTANK joint project is to make a significant contribution to the development of tanks made of carbon fibre reinforced plastics (CFRP) for cryogenic hydrogen storage in order to realise emission-free passenger aircraft. CFRP offers immense lightweight construction potential compared to available metallic tanks, which is of particular importance for aircraft with longer ranges. The HYTANK consortium therefore aims to develop resource-efficient processing and assembly methods for liquid hydrogen tanks made of CFRP and to implement and test them in production technology. TU Dresden is focusing on the experimental clarification and mathematical description of the influence of liquid hydrogen on the behaviour of the joining partners in the laminate thickness direction, the damage to the adhesives and the resulting bonded joints. The development of customised methods for tests in a cryogenic environment is the main focus here. In addition, the curing process of the adhesives is analysed with regard to its reaction kinetics in order to demonstrate the most energy-efficient process control possible. The joining process is evaluated in the consortium using LCA.

Cryostat for Testing in Liquid Hydrogen (LH2): Five photos shown side by side: measurement cryostat, cross section of the test setup, drive unit detail, specimen gripping system detail, and load tube in the assembly fixture. — Fig. 01: Cryostat for Testing in Liquid Hydrogen (LH2).

The test results obtained for the preferred adhesives selected in the project at four temperatures (296 K, 77 K, 20 K, and 4 K) clearly demonstrate the significant changes in material properties that occur as adhesives are cooled into the cryogenic temperature range. The stiffness increased substantially for all adhesives investigated (Fig. 2), while the strength exhibited a more differentiated response (Fig. 3). It should be noted that testing at 20 K was conducted under exposure to liquid hydrogen.

Diagram showing the elastic modulus of different adhesives at various temperatures. — Fig. 02: Elastic Modulus for Different Temperatures and Adhesives.

Chart comparing the elastic modulus of different adhesives as a function of temperature. — Fig. 03: Strength Comparison for Different Temperatures and Adhesives.

Developing a functional adhesive model capable of accounting for cryogenic temperatures required additional investigations of various adhesive joints. These were tested at five different temperatures and three adhesive bondline thicknesses. Figure 04 shows the results of the 45° tensile test.