Issue 10

A. Pirondi, Frattura ed Integrità Strutturale, 10 (2009) 21-28; DOI: 10.3221/IGF-ESIS.10.03 23 To account for the elasticity of the adhesive, the DCB specimen can be modeled as a beam on an elastic foundation, where the foundation modulus, k, will depend on the elastic constants of the adhesive (i.e. E a and  a ) and on the bondline thickness, t. The solution developed in [14] n eglecting shear contributions was therefore considered. The load line compliance is given by the following equation:                       3 2 ' a a 3 2 a 2 a 21 bE t 2 P C (2) where E’ a =E a /(1-  a 2 ) is plane strain modulus of the adhesive and E 'E th 6 EI k4 a 3 4     . The strain energy release rate G is given by 2 2 2 2 a 1 1 bEI aP a C b2 P G                   (3) For the present DCB specimen the term (   a) -1 is about 0.25. T-peel tests A series of tensile tests was conducted at the Polytechnic of Turi n [15] on UNI Fe360 construction steel T-peel joints (Fig. 2). Figure 2 : Outline of half of the 1.5mm-thick T-peel joint tested in [15]. A metal sheet thickness of 1.5mm was investigated. The adhesive used is again the Loctite 330  . A bondline thickness of 0.1mm was obtained in this case. Displacement-controlled tests were conducted up to partial or complete separation of the two halves. M ODELLING Fe models he 2D FE models corresponding to DCB and T-peel joints are shown in Figs. 3a-b. Symmetry conditions with respect to the bondline have been applied. Plane stress, eight-noded isoparametric elements have been used to simulate the metal adherend. The cohesive zone has been modelled with the cohesive elements available in the FE code ABAQUS. A convergence analysis was preliminarly conducted to determine the appropriate element size. The presence of the adhesive layer was either included in the cohesive zone (Adherend + Cohesive Zone, ACZ) or explicitly modelled with four-noded, hybrid, plane strain elements (Adherend + Adhesive + Cohesive Zone, AACZ), as done for example in [11]. The number of elements along the thickness of the bond was defined so far according to the indications given in [16] . In the case of the T-peel joint, different extensions of the adhesive layer at the fillet were simulated, since they were not known in detail. 150 1.5 50 20 = = 10 8 R5