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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Fig. 14. P- δ curves for SLJ with Araldite: a) unaged condition; b) aged condition in tap water (desorption); c) aged condition in sea water (desorption).

3.5 Interface slip and strength: fracture propagation Considering the bilinear shape of the interface law introduced in section 3.2 and fixing the value of the fracture energy equal to the one experimentally obtained ( �� , � � ), that of the shear strength ( � ) equal to the yield strength furnished by the supplier, the ultimate slip ( � ), which corresponds to the complete separation between the adherents, is easy to evaluate. This assumption about the shear strength is very common in the numerical simulations, given that the real relation between the shear strength and the yield strength is uncertain [Xu et al 2012]. Nevertheless, the stiffness of the elastic branch is unknown if the slip corresponding to the shear strength is unknown. Through the FEM model previously described, all the values characterizing the interface law were evaluated with particular regard to the absorption only. Corresponding to the first point of the adhesive layer (notch side) of Figure 6, each interface law was built recording all the shear stress values increasing the load with a monotonous law. The slip corresponding to the shear strength is very little compared to the ultimate one (about 1/100). Furthermore, in order to validate the FEM model in terms of the fracture propagation, a comparison between the experimental and numerical results was performed. Within this scope, referring to Figure 15, the trend of the maximum shear stresses was depicted in function of the adhesive layer length. It resulted 60 mm for SikaDur 30 (for a total of 120 mm considering a o =60mm) and 70 mm for Araldite (for a total of 140 mm). After that, for several nodes (Figure 16) positioned inside this part of the adhesive layer, the conjugated interface laws were evaluated highlighting how the decrement in terms of � correspond to that one experimentally observed.