PSI - Issue 47

Francesco Ascione et al. / Procedia Structural Integrity 47 (2023) 826–841 Author name / Structural Integrity Procedia 00 (2019) 000–000

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As can be observed, the desorption phenomenon gives the adhesive an increment in terms of stiffness and strength leading the adhesive to its unaged condition. In detail, the degradation observed during the absorption period was due to plasticization effects only (and not due to hydrolysis also), considering the almost complete recovery of the strength properties in terms of fracture energy in mode II. Both in the case of sea water and tap water conditioning, the value of the energy fracture �� , � � , after the desorption is greater than that of the unaged condition. This is an expected result taking into account the effect of the post curing phase, activated by the temperature of the water equal to 30°C (greater than that of the curing phase of the SLJ samples at 23°C), for which the fracture energy in the first three-four months of immersion increased reaching a value twice with respect to the unaged condition. Finally, in Figure 5, all the experimental P- δ curves for the unaged and aged specimens (desorbed) are depicted. It is evident that not only the strength but also the stiffness is almost recovered after the desorption period.

Fig. 4. Experimental P- δ curves for unaged and aged specimens: a) SikaDur30; b) Araldite.

3. Finite element modelization 3.1 Mesh details and boundary condition of the 2D model used for ENF test

In this sub-section, a numerical model of the single lap joint (suitable for ENF test) is built with the commercially available FEM code Abaqus. Being the width of the adherents larger (2,5 times) than their thickness, the adhesive joint modelization could be simplified by taking into account the elastic-plastic plane strain problems (2D problem). The scheme of the joint is that one already presented in subsection 2.1 where the adherents are in GFRP. Consequently, the five mechanical parameters which describe their mechanical behaviour are reported in Table 3, where the plane 2-3 is the plane of isotropy.