Issue 10

A. Pirondi, Frattura ed Integrità Strutturale, 10 (2009) 21-28; DOI: 10.3221/IGF-ESIS.10.03 25 R ESULTS Tuning of CZ parameters he first step was the tuning of the DCB-ACZ model on the related experiment performed in [13]. Some parameters were pre-calibrated based on the results shown in a previous work [12]. Therefore, a value of  m =5MPa was adopted in all of the models and in the case of the trapezoidal law, c 1 =0.2 and c 2 =0.5 were taken, as tipically found in the literature. It is visible in Fig. 5 that with such a cohesive law the propagation phase is well matched and the peak load is only slightly overestimated, but initial slope is quite different. Much better results are obtained instead with a triangular law with c 1 =0.01. A similar agreement (not shown here for the sake of clarity) was found with the trapezoidal law using c 1 =0.01 and c 2 =0.02, in fact an almost triangular law. The exponential law was taken with a  1 equal to the  1 defined for the triangular law in order to keep the same initial slope. Anyway, this choice resulted in a lower peak load and a different post-failure trend with respect to the triangular law. Specifically, it resembles the results that would be obtained using a lower value of  m . All of the following simulation were therefore conducted using the triangular law, which incidentally is also easier to handle. Figure 5 : Tuning of ACZ model on DCB experiment. The value of  m =5MPa outcome from the ACZ tuning is only a bit higher than the yield strength of the adhesive (4.8MPa). The calibration of AACZ parameters was attempted using couples of (  0 ,  m ) lower and higher than the values obtained for the ACZ model, respectively, as shown in [11]. Anyway, since the value of  m =5MPa outcome from the ACZ tuning is only a bit higher than the yield strength of the adhesive (4.8MPa), plasticity within the adhesive layer is not significant and the AACZ model did not significantly differ from the ACZ. Simulation of T-peel tests The simulation of T-peel tests was conducted using an ACZ model with  m =12.5 MPa to take into account the higher adesive layer stiffness of the T-peel joints with respect to the DCB due to the different thickness (i.e. 0.1mm against 0.25mm) and  m =20.6 MPa, to take into account also the higher strength when joining steel (T-peel) instead of aluminum (DCB), as described in the technical datasheet of the adhesive. The results shown i n Fig. 6 in the case of a 1.5mmthick T- peel arm exhibit a good correlation with the experiments in the propagation phase but a very poor match in the loading phase, regarding both the slope and the peak load. On the other hand, it is known [11] that in very thin adhesive layers as in the present case plasticity is strongly confined and due to this, the value of  m of an ACZ model increases with decresing adhesive layer thickness. T