Rate-dependent degradation of moisture- absorbed adhesive joints

Mechanical performance of polymer-based adhesive joint is susceptible to moisture absorption. This study quantifies the effect of absorbed moisture on the strength, stiffness, and energy properties of adhesive bonded joints. For this purpose, moisture absorption characteristics of structural adhesive joints (Araldite2015) with different thicknesses (0.5, 1.0, and 1.5 mm) are established under accelerated aging conditions (deionized water at 60 oC). A thickness-dependent two-phase moisture absorption model was used to characterize moisture absorption of the adhesive joints. Results show that the moisture absorption of the adhesive joints is governed by capillary action. Adhesive joint specimens with aluminum 6061 adherents and 0.5 mm-thick Araldite 2015 adhesive compound are subjected to dry and 0.2 % moisture content. The specimens are tested in shear and tension under rate-dependent loading condition of 5, 50, 250, and 500 mm/min. The variations in the properties which are strength, stiffness and strain energy density are calculated from the rate- dependent load response. The properties of dry adhesive joint significantly increases with the test speed, while minor increase in similar effect on stiffness properties for ageing adhesive joints. Meanwhile, for the failure modes, mixed-mode failure is dominating at all loadings directions.