Examination of film and paste adhesive behaviour under cryogenic conditions using a thick adherend shear test

Kurzfassung

Carbon fibre reinforced polymers (CFRP) are key enablers for lightweight liquid hydrogen storage in aerospace applications. Adhesive bonding provides a structurally efficient and inherently leak-tight method for joining CFRP and hybrid substrates, offering clear advantages over mechanically fastened joints. While most studies focus on shear stress due to the technica difficulty of measuring strain at cryogenic temperatures, the brittle nature of epoxy adhesives under these conditions makes it crucial to establish clear shear strain limits to ensure both leak-tightness and structural performance. This study introduces a methodology for characterising structural film and paste adhesives using thick adherend shear tests under cryogenic conditions. The approach incorporates the development of a dedicated cryogenic test rig (CryoTAST) and the adaptation of a custom-built capacitive extensometer suitable for use at cryogenic temperatures. Shear properties of four adhesives were determined in accordance with ASTM D5656. Furthermore, the influence of manufacturing variability was assessed by evaluating three bondline thicknesses per adhesive. The results provide essential input data for the robust design and qualification of adhesively bonded joints in CFRP liquid hydrogen tanks, supporting both their mechanical performance and leak-tightness under extreme environmental conditions.