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. 2. Representative experimental P- δ curves of SLJ specimens with SikaDur 30 and Araldite. N.B. Elastic, post-elastic as well as fracture propagation zones are relative to the Araldite case.

The critical fracture energy value in mode II was estimated using the Compliance-Based Beam Method (CBBM) presented and validated in [26]. The analytical expression of the fracture energy is the following: � � � ��� � 9 � �� � � �  2 � 3 �� � 2 � � (1) In Eqn. (1), the symbols introduced assume the following meaning: P is the applied load, B is the specimen width, L is the span length, � is the initial crack length, � is the equivalent crack length while �� is function of � which is the measured initial compliance of the P- δ curve. Representative experimental R-curves for SLJ specimens are presented in Figure 3, where the ductile behaviour of Araldite respect to the brittle behaviour of SikaDur 30 can be easily observed again.

Fig. 3. Representative experimental R-curves of SLJ specimens for both epoxy resins (SikaDur 30 and Araldite). N.B. Fracture propagation zone is relative to the Araldite case.

In Figure 3, three different values of the fracture energy in mode II were evaluated for each SLJ specimen: �� , � �� , �� , � ��� and �� , � � . They are strictly connected to the three values of the load P of Figure 2. In detail, �� , � �� is the fracture energy corresponding to the load �� (in this case no FPZ is taken into account and then the equivalent crack length, � , coincides with the initial crack, � , equal to 60mm); �� , � ��� is the fracture energy corresponding to load ��� (the whole post-elastic zone is taken into account and � is greater than � ); �� , � � is the maximum fracture energy relative to the load � corresponding to the stop of the crack evolution (crack moves from an