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7 Virtual testing approach for sandwich panel joints
Stage ③ represents another linear regime, where the load increases despite previous
core damage. In this stage, the shear transmission of the damaged core is reduced, leading to a change of the load path. From this point onwards, the bond between adhesive
and lower face experiences increased stress. This is also visible in the exterior live observation of the test, where the bonded surface area between these two constituents is
decreasing throughout this stage (Figure 73, page 98). At the same time, the core damage progresses and shear damage initiation of the increasingly stressed top face sheet is
visible by the end of the stage.
Stage ④ marks catastrophic failure of the structure, which is evident by a sudden 50%
load drop. This failure occurs not before adhesive and bottom face sheet have fully
debonded.
Stage ⑤ represents the post failure regime. Here, rupture of the upper face sheet and
debonding of upper face sheet and core occurs.
Since it is not required to predict the post failure regime accurately, the two effects in
stage ⑤ are of secondary interest in the example. The relevant mechanical effects are
therefore all effects, that occur in stages ②-④. The virtual test method is required to
enable the prediction of these mechanical effects. They are summarized as follows.
Core shear failure
Face shear damage
Adhesive to face debonding
With the mapping of the damage mechanisms to the test progression and the identification of the relevant mechanical effects the problem analysis phase concludes. The following section addresses the definition of the model framework for the virtual test.
7.3 Phase 2 - Definition of model framework
The objective of Phase 2 is to set the framework for the FE-models to be developed in
Phase 3. The definition of the model framework depends on the previously identified list
of relevant mechanical effects. It can be subdivided in three general steps. Firstly, the
level of detail of the virtual test model is defined. Subsequently, the time integration
method is selected. The combination of level of detail and time integration method
makes up the model framework. In the last step, the model framework is evaluated. In
case the framework is evaluated as not suitable, an iteration loop leading back to the
definition of level of detail is required. This last step is implemented to ensure that the
model framework is defined with care. If the framework is changed later on, considerable rework is required. A flow chart of phase 2 is illustrated in Figure 82.
7 Virtual testing approach for sandwich panel joints
Stage ③ represents another linear regime, where the load increases despite previous
core damage. In this stage, the shear transmission of the damaged core is reduced, leading to a change of the load path. From this point onwards, the bond between adhesive
and lower face experiences increased stress. This is also visible in the exterior live observation of the test, where the bonded surface area between these two constituents is
decreasing throughout this stage (Figure 73, page 98). At the same time, the core damage progresses and shear damage initiation of the increasingly stressed top face sheet is
visible by the end of the stage.
Stage ④ marks catastrophic failure of the structure, which is evident by a sudden 50%
load drop. This failure occurs not before adhesive and bottom face sheet have fully
debonded.
Stage ⑤ represents the post failure regime. Here, rupture of the upper face sheet and
debonding of upper face sheet and core occurs.
Since it is not required to predict the post failure regime accurately, the two effects in
stage ⑤ are of secondary interest in the example. The relevant mechanical effects are
therefore all effects, that occur in stages ②-④. The virtual test method is required to
enable the prediction of these mechanical effects. They are summarized as follows.
Core shear failure
Face shear damage
Adhesive to face debonding
With the mapping of the damage mechanisms to the test progression and the identification of the relevant mechanical effects the problem analysis phase concludes. The following section addresses the definition of the model framework for the virtual test.
7.3 Phase 2 - Definition of model framework
The objective of Phase 2 is to set the framework for the FE-models to be developed in
Phase 3. The definition of the model framework depends on the previously identified list
of relevant mechanical effects. It can be subdivided in three general steps. Firstly, the
level of detail of the virtual test model is defined. Subsequently, the time integration
method is selected. The combination of level of detail and time integration method
makes up the model framework. In the last step, the model framework is evaluated. In
case the framework is evaluated as not suitable, an iteration loop leading back to the
definition of level of detail is required. This last step is implemented to ensure that the
model framework is defined with care. If the framework is changed later on, considerable rework is required. A flow chart of phase 2 is illustrated in Figure 82.