Issue 10

A. Pirondi, Frattura ed Integrità Strutturale, 10 (2009) 21-28; DOI: 10.3221/IGF-ESIS.10.03 26 Figure 6 : Comparison between experiment and T-peel simulations (ACZ model). The simulations done with the AACZ kind of model are shown in Fig. 7 i n the case of 1.5mm-thick peel arm. The use of the parameters determined from DCB (  m =5MPa,  0 =550J/m 2 ), where ACZ and AACZ were coincident, resulted in a large difference with the experimental behavior. Figure 7 : Comparison between experiment and T-peel simulations (AACZ model). From these analyses, it is evident that CZ parameters may not be the same for the nucleation and propagation of a crack. Besides discrepancies that may arise between the properties of bulk adhesive and joint, and between different joint geometries due to the bonding process, where adhesive and activator cannot be pre-mixed in a fixed ratio, it has been demonstrated that the tearing process is influenced by the local constraint [11]. Therefore, a further analysis has been attempted using AACZ modeling where: i) the adhesive was extended at the fillet, with the extension length limited by the maximum adhesive thickness that can be polimerized according to the supplier datasheet; ii) the cohesive strength  m has been defined as the value of stress in the adhesive normal to the plane of the joint, at the point in the analysis where the uniaxial failure strain was met locally. The distribution of cohesive strength obtained in this way is shown i n Fig.8. The results of the simulation with the cohesive law input from Fig. 8 and  0 =550J/m 2 reported in Fig. 9 show a neat increase of the agreement with the experiment concerning the phase up to the maximum load, while the crack propagation phase is matched well as in the previous analyses. This fact confirms that the crack propagation may be reproduced quite easily tuning the CZ parameters on standard fracture experiments, while the nucleation requires specific