Issue 47

F. Moroni et alii, Frattura ed Integrità Strutturale, 47 (2019) 294-302; DOI: 10.3221/IGF-ESIS.47.22 297 a) b) Figure 4 : Finite element models used to obtain the G values for DCB (a) and ENF (b) joints. A detailed view of the mesh refinement is also reported for the DCB model. Quadrangular elements are used; the mesh size in the adherends ranges between 0.4 mm and 0.02 mm, while in the adhesive layer it ranges between 0.03 mm and 0.02 mm. A linear elastic behavior is assigned to the adherends and adhesive, using the mechanical properties reported in Tab. 1. The values of G I and G II are obtained as the average of the J-integral output in 7 contours surrounding the crack tip. Also the crack-length vs. compliance relationship is evaluated numerically by FEM and input to the test control software. Three-point bending experiments were performed for the identification of the flexural and shear modulus of the composite adherent, to be used in FE simulations. Since in ENF tests the crack is not open and the compliance is less sensitive to crack length changes than in DCB tests, the crack tip position was evaluated at unloading points during the test by DIC (Digital Image Correlation) on the specimen side. The DIC values of crack length were then compared for validation to crack lengths obtained by inverse FE analysis of the unloading compliance. However, in ENF no R-curve was detected due to unstable crack propagation from the initial length to below the loading point. Co-cured composite specimens have the same dimensions and methodologies of the co-bonded ones but without using the adhesive film. Also, the overall thickness is 13 mm instead of 5.7x2=11.4 mm due to a small excess of resin in the laminate. Test conditions for mode I or mode II delamination are the same of co-bonded joints. Five repetitions were done for tensile tests and three repetitions for fracture tests. R ESULTS AND DISCUSSION Tensile strength esults will be presented scaled with respect to the tensile strength of the co-cured CFRP for the sake of confidentiality. Therefore, diagrams show normalized values denoted as S max_norm and for co-cured CFRP the average value of S max_norm is equal to 1. For analogous reasons, the value of force in force-opening diagrams is normalized with respect to the maximum force of the same test, F max . R