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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Preliminary, the choice to model the thickness of each adherent by 20 elements was validated by making a comparison between a FEM model and the closed form solution of a simply supported Timoshenko beam. The parameter selected for the convergence test was the deflection at mid-span, U 2 (Figure 7).

Fig. 7. Convergence test: mid-span deflection vs number of elements along the thickness.

3.2 Cohesive zone model assumption

The cohesive law adopted in this study is the bilinear one being the best and simplest law to model the behaviour of resins under investigations as shown in [Ascione et al. 2021]. In Figure 8, the traction separation law in shear is depicted. The symbols introduced assume the following meanings: � is the ultimate shear stress, � is the sliding (relative horizontal displacement between adherents) at the limit elastic stage, while � is the sliding corresponding to the complete separation between adherents.

Fig. 8. Traction-separation law in mode II.

The interfacial fracture energy can be expressed by the following formulation: �� , � � �� � � � � 1 2 � �

(2)

The loading is supposed monotonically increased, then the interface begins to soften and to degrade, when the damage starts. The interfacial damage occurs when the quadratic nominal stress criterion is satisfied: