Issue 19

G. Bolzon et alii, Frattura ed Integrità Strutturale, 19 (2012) 20-28; DOI: 10.3221/IGF-ESIS.19.02 25 Figure 8 : Evolution of the left ( a , continuous line: reference image 7; a , dashed line: image 22 ) and of the right ( b : reference image 7, c : image 40) boundary between the aluminium laminate and the paperboard composite during the tensile test; in (b) and (c) , two reference lines close to the interface where fracture develops (one on the paper side, one on the aluminium side) are separately monitored. Figure 9 : Recovery of the relative displacements during material separation from images 7, 22, 27, 32 (left to right). The actual values of the fracture parameters relevant to the investigated material samples can be recovered by the inverse analysis procedure introduced in the next Section, based on the comparison between the results of the experiment and the corresponding output of the test simulation. The reduced FE model shown in Fig. 10(b) is implemented to this purpose. The investigated domain consists of the aluminium inclusion only. Suitable boundary conditions, deduced from the performed DIC measurements (shown in Figs. 8 and 9), are applied along the lines (coloured in Fig. 10b) that represent the interface with the surrounding packaging material. In this way, the cumbersome calibration of the mechanical properties of the paperboard composite is avoided and the relevant uncertainties do not affect the identification result. The FE model is completed by the insertion of non-linear spring elements along the side where fracture propagates. Figure 10 : Schematic representation of the assumed traction − separation law and the reduced FE model exploited for identification purposes. (c) (b) (a) (a) (b)