**6. Indentation Test**

There are several standard tests for Cohesive Zone Elements, e.g. the double cantilever beam test or the end notch flexure test. However, they focus on shear or normal separation induced delamination. Therefore, an indentation test is used here that is influenced by membrane modes as well. A sandwich of 20 mm × 4 mm steel (upper part) and 20 mm × 4 mm aluminium (lower part) is compressed by a cylinder with a radius of 6 mm. The simulation is carried out in 3D but boundary conditions are applied to enforce plane strain conditions. Furthermore, symmetry conditions are utilised. The parameters for the joining zone are adopted from Section 4.3, for the bulk materials room temperature is assumed and accordingly yield stresses of <sup>σ</sup>*y*,*st* = 600 MPa and <sup>σ</sup>*y*,*al* = 400 MPa [10].

Figure 16 shows some increments of the simulation using a fine mesh. Predamaging, failure, and successive delamination can be observed. The contact algorithm adopted from [5] maintains a certain stiffness in normal direction only for compression. Therefore, penetration after failure is prevented but tangential sliding occurs.

The simulations are carried out with 10, 20, 30, 40, 50, and 60 elements in horizontal direction. Table 1 contains the increment and position of failure initiation for the different meshes. The three finer discretisations lead to very similar results regarding failure initiation.


**Table 1.** Location and increment of failure initiation.

**Figure 16.** *Cont.*

**Figure 16.** *Cont.*

**Figure 16.** Indentation test: Joining zone damage: increment 0 (**a**), 10 (**b**), 20 (**c**), 30 (**d**), 36 (**e**), 37 (**f**), 38 (**g**), 39 (**h**), 40 (**i**), 50 (**j**).
