The durability of adhesively joints in space structure during interplanetary exploration

Abstract

Spacecrafts are subjected to very few mechanical loads but in the future with reusable spacecraft designed for interplanetary explorations and with the repetition of landing and take off, structures will be subjected to significant mechanical loads. The degradation due to space aging conditions, of the adhesive materials used as joints in space structure is not known yet for such a reusable spacecraft on long term exploration. Two adhesives used in spacecraft structures were investigated: Scotch-Weld EC-2216 and Scotch- WeldTM EC-9323-2. Those adhesives were exposed to two aging conditions from a space environment point of view: (1) electron irradiation using a Van de Graaf particle accelerator and (2) thermal vacuum cycling. Change in the adhesives properties was assessed before and after space environment exposure to understand related effect on their mechanical performance using CFRP and aluminium adherents, including, tensile tests, peel tests, double cantilever beam (DCB) tests, as well as evolution of their intrinsic properties by mean of dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and fourier transformed infrared spectroscopy (FTIR). It has been found that electron irradiation accelerates the completion of the curing reaction in EC-2216 and reduces fracture toughness, peel load, Young’s modulus, tensile strenght for both adhesives, which degrade adhesion integrity. The effects of thermal vacuum cycling on adhesives and adhesion differ, with certain attributes being reduced as Young Modulus, tensile strength or glass transition temperature and others being increased as fracture toughness. Effects of space environment are visible and very significant on these adhesives. The results of this study form a preliminary basis for long term prediction of adhesive bond behaviour in space.