Thermal ageing of bonded assemblies. Effect of adhesive curing degree

This paper reports the failure of bonded assemblies submitted to thermal ageing. Adhesives are either fully or incompletely cured. Despite comparable initial properties, depletion of mechanical properties (evaluated from single las shear tests) is faster in the case of incompletely cured polymer. A series of comprehensive experiments were conducted on thin films of adhesive itself and some model systems based on its main components. According to tensile tests and kinetic curves of stable oxidation products detected by Infrared spectroscopy, fully cured epoxy would oxidize faster (because of greater concentration in oxidizable sites). Oxygen diffusivity was observed to be comparable in both systems. It results in a lower thickness of degraded layer in the case of fully cured samples, which explain the results obtained in bonded assemblies.