PSI - Issue 39

M.R.M. Aliha et al. / Procedia Structural Integrity 39 (2022) 393–402 Author name / Structural Integrity Procedia 00 (2021) 000–000

400

8

The failure path in the adhesive subjected to the pure mode I condition is shown in Figure 7. Based on this Figure it can be seen that for pure mode I condition, the crack growth is in the adhesive layer and the propagation path is along the direction of the initial crack and inside the adhesive that results a cohesive fracture type for pure tensile mode loading.

Fig. 7. (a) Crack growth under pure mode I (α = 0 o ) , (b) Crack initiation in the first element of adhesive, and (c) Crack propagation through the adhesive elements.

Part (a), (b), and (c) of figure 8 shows the failure path subjected to the pure mode II condition. On the contrary of pure mode I, crack propagation path kinks towards the adherent-adhesive interface for pure mode II and mixed-mode I/II conditions. These phenomena occur inside the XFEM enrichment zone. The degree of degradation of the enriched element in the XFEM is given by the STATUS parameter (defined in ABAQUS code); with STATUS =0 relating to the undamaged degradation and STATUS=1 to complete failure [18]. Based on part (d) of Figure 8, as the crack reaches the adherent-adhesive interface, crack development in the XFEM domain stops and cohesive surface starts to show the damage. Also based on part (e) of Figure 8, with increasing the loading, delamination starts to propagate at the interfaces between the adhesive and the adherents. The degree of degradation of the cohesive surface is given by the stiffness degradation parameter (i.e. CSDMG defined in ABAQUS code); with CSDMG =0 relating to the undamaged degradation and CSDMG=1 to complete failure [18].