Issue 30

D. Gentile et alii, Frattura ed Integrità Strutturale, 30 (2014) 252-262; DOI: 10.3221/IGF-ESIS.30.32 260   2 0 0 1 3 2 cr cr cr J P d P r                (6) where P is the applied load,  cr is the load point displacement which is function of the compliance of the uncracked specimen, and r 0 is the uncracked ligament. Results are provided in Fig. 11. 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 FEM CCB_1 CCB_2 J-INTEGRAL [kJ/m 2 ] CRACK ADVANCE  a [mm] Figure 11 : Comparison of calculated crack resistance and crack driving force obtained using unloading compliance values. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 J-INTEGRAL [kJ/m 2 ] CRACK ADVANCE  a [mm] FEM CCB_B1 compliance corrected Figure 12 : Crack resistance curve calculated considering the change in the unloading compliance. It can be seen that the agreement is good up to J-integral values of ~600 N/mm, which correspond to the maximum load. This is coherent with Eq. (6) that is valid up to the maximum load. Beyond this point, Eq. (6) shall be corrected considering the change in the unloading compliance due to crack advance. Therefore, crack resistance data have been recalculated using the unloading compliance measured in the tests. The new crack resistance curve is shown in Fig. 12. This time, a better agreement between the experimental values and the FEM results is found up to ~1.0 mm of crack growth.