Post-cure and γ-irradiation effects on the elastoplastic behavior of structural epoxy adhesive bulk specimens

The present work studies the effects of γ-irradiation on 3M™ Scotch-Weld™ EC-2216 B/A Gray, a commercial two-part flexible epoxy adhesive. The study aims to determine its mechanical characteristics by tensile testing bulk adhesive specimens and quantify the effect of different γ-ray doses (generated from a 60Co source) on the mechanical behavior of the adhesive. The elastoplastic stress-strain curve of the adhesive has been described until failure, varying the absorbed dose up to 500 kGy. Furthermore, a behavior evolution of the adhesive after the cure has been observed and described. The mechanical stabilization occurs between 48 and 85 days after the nominal end of the cure. It has been found that young specimens show a behaviour well described with a two-parameter power law, while for the other specimens, the Ramberg-Osgood model is more appropriate since it can also modelize their initial linear trend. A crosslinking increment can be hypothesized during this period, which could justify the overall embrittlement and stiffening of the adhesive. The adhesive, on the whole, has good mechanical stability after irradiation in the inspected interval, showing a reduction of Young’s modulus. Tensile strength and elongation at break result being quite stable with the absorbed dose, though the statistics for those parameters is poor because of the relevant quantity of invalid fractures. Attenuated Total Reflection Fourier Transform Infrared spectroscopy (ATR-FTIR), Electron Paramagnetic Resonance (EPR) spectroscopy, and colorimetric analysis have also been performed to investigate the modifications induced by γ-irradiation.