Sustainable aviation demands alternative propulsion system, such as Liquid Hydrogen (LH2). LH2 needs to be cryogenically stored in large, lightweight fuel tanks. Carbon-fibre Reinforced Polymer (CFRP) composite tanks offer promising weight-savings.

Liner-less composite tanks are prone to safety-critical issues such as leakage. Leakage is caused by the presence of microcrack networks in the laminate. It is known that these crack networks arise due to thermo-mechanical loads. Element level testing is required to build a foundational understanding of the damage and leakage phenomena. The bulge test rig is capable of such element level testing, by mimicing multi-axial loads experienced by the tank structure at cryogenic temperature.

A digital twin is developed to provide deeper insights into the behaviour of the test rig and specimen. The validity of this digital twin is quantified by a 'multi-sensor' experimental campaign. The validation dataset is obtained on a range of test configurations, both at room and cryogenic temperature. Specifically, strain data is acquired using strain gauges, fibre-optic sensors and digital image correlation. Qualitative damage assessment of post-mortem specimen is conducted using ultrasound and optical microscopy, to compare the inter and intra-laminar damage initiation predictions of the digital twin.

The experimental-numerical analysis of the work is envisioned to contribute to a more representative design of bulge test specimen.

Hydrogen is one of aviation's most promising fuel alternatives in the coming years. However, to store it, a large and light vessel is needed.

The solution to this problem can be the carbon fibre fuel tank. Composite structures provide significant weight savings, which is crucial in this application. However, despite its superior performance, the hydrogen molecules permeate through the CFRP tank wall. Hence, researchers must first understand the driving phenomena to design a safe and robust hydrogen tank. The only proven way to do this is through experiments, but they must also be carefully considered to deliver representative results.

In this research, the question of how to perform the permeation and leakage testing of the CFRP laminates to accurately represent the behaviour of a full-scale hydrogen tank is being answered. The numerical analysis method has been used to evaluate different testing parameters and aid the development of the new testing rig. This thesis is the collaboration between the TU Delft and the DLR.