Etude du vieillissement d'un assemblage métal/adhésif/métal par impédancemétrie électrique et viscoélasticimétrie

The changes in the electrical features of bonded joints stainless steel/adhesive film/stainless steel are followed against aging time in a hot moist environment by using non-destructive electrical impedance measurements. It is shown that the ingress of moisture into the bonded joint leads to a decrease in resistance at low frequencies and to an increase of the dielectric constant of the adhesive. This sorption of water results from two simultaneous processes: - bonding of water molecules with the active sites of the polymer chains leading to a relaxation at low frequencies. - diffusion of free water in the bonded joint, leading to an increase in the permittivity of the adhesive at high frequencies. The relative proportion of the bonded water and free water is also given. In addition, it is shown that the water sorption kinetics varies with the nature of the surface pretreatment of the metallic substrate. All these data are in agreement with those obtained by dynamic mechanical thermal analysis.