Development of a robust measurement method for determining the mechanical properties of adhesives under cryogenic conditions based on thick tensile shear specimens according to ASTM D 5656

Kurzfassung

The demand for cryogenic adhesive characteristic values is increasing. In this thesis, various test methods and standards for mechanically characterising adhesives are compiled from existing literature. The CryoTAST test setup for cryogenic characterisation is presented. The CryoTAST test setup uses liquid nitrogen (LN2) to generate the required cryogenic test environment. Measurement methods to determine the mechanical parameters in those conditions are strain gauges, fibre optic systems and extensometers. To improve the sensor signal, a sensitivity analysis of the used capacitive extensometer on a specially developed test rig is performed. Various parameters, including gap size, grounding and contamination, are analysed for their infuence. A signifcant infuence of the liquid nitrogen on the sensor signal was found. The parameters of a bubble shielding, gap size, amount of cable in the LN2, sensor orientation and contamination showed also a great infuence on the stability and accuracy of the signal. Based on these results, measures toreduce the interference are developed. Followed by a validation of the test procedure and subsequent determination of the characteristic values of the EA9695 epoxy adhesive with a thick-adherent shear test (TAST). The residual stresses due to the difference in the coeffcient of thermal expansion (CTE) of the adhesive and the adherent need to be quantifed in simplifed calculations. Finally, the aim is to develop a test guideline for the CryoTAST test stand, which contains the collected findings.