7.4 Phase 3 - Model development
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calibrated. The compressive strength and the shear modulus characterization have been
determined in the following structural elements building block.
Structural element level
Considering the bilateral adhesive bond between the constituents, the debonding of face
and adhesive/potting has been established as the only relevant mechanical effect during
the problem analysis. Therefore, the remaining interfaces between the constituents can
be modelled as tied contact (kinematic coupling). As described earlier, the face to adhesive bond is generally addressed on sub-component level. Hence, the only investigation
which has been performed on structural element level is the completion of the face
sheet material model based on tests on the bonded sandwich panel. Here, the face shear
properties are of particular interest, since face shear failure has been established as relevant mechanical effect. In addition, the compressive strength of the face sheets has not
been determined on constituent level. In order to determine the missing material properties, the corresponding investigation has been based on two structural tests. These are
described in the following.
Sandwich panel bending
The first structural test of the investigation is flexural bending, which enables to determine the compressive strength of the prepregs. The full study, which contains additional
face sheet lay-ups is described in section 5.1. This study confirmed and validated the
elastic face sheet and core properties from the constituent level. In addition, the existing
face sheet material model has been complemented by the compressive damage behavior. Regarding the core, it is shown that the honeycomb modelling approach determined
on constituent level is able to predict the correct failure mode also on structural element
level.
Frame shear
In order to determine the shear properties of the face sheets, sandwich panels with the
same lay-up as in the reference test were additionally subjected to in-plane shear according to the standardized picture frame shear test. Using inverse problem methods,
the existing face sheet model has been complemented by the elastic and plastic shear
properties based on the experimental results. The fully calibrated face sheet material
model reproduces the performed shear test results in terms of both stress-strain relationship and face sheet fracture progression. The corresponding experimental and numerical studies are described in detail in section 5.2.
Summary
The structural element building block concludes with validated elastic constituent material properties of face sheet and core as well as a fully calibrated face sheet material
model including compressive and shear strength properties. Since no fracture of the core
129
calibrated. The compressive strength and the shear modulus characterization have been
determined in the following structural elements building block.
Structural element level
Considering the bilateral adhesive bond between the constituents, the debonding of face
and adhesive/potting has been established as the only relevant mechanical effect during
the problem analysis. Therefore, the remaining interfaces between the constituents can
be modelled as tied contact (kinematic coupling). As described earlier, the face to adhesive bond is generally addressed on sub-component level. Hence, the only investigation
which has been performed on structural element level is the completion of the face
sheet material model based on tests on the bonded sandwich panel. Here, the face shear
properties are of particular interest, since face shear failure has been established as relevant mechanical effect. In addition, the compressive strength of the face sheets has not
been determined on constituent level. In order to determine the missing material properties, the corresponding investigation has been based on two structural tests. These are
described in the following.
Sandwich panel bending
The first structural test of the investigation is flexural bending, which enables to determine the compressive strength of the prepregs. The full study, which contains additional
face sheet lay-ups is described in section 5.1. This study confirmed and validated the
elastic face sheet and core properties from the constituent level. In addition, the existing
face sheet material model has been complemented by the compressive damage behavior. Regarding the core, it is shown that the honeycomb modelling approach determined
on constituent level is able to predict the correct failure mode also on structural element
level.
Frame shear
In order to determine the shear properties of the face sheets, sandwich panels with the
same lay-up as in the reference test were additionally subjected to in-plane shear according to the standardized picture frame shear test. Using inverse problem methods,
the existing face sheet model has been complemented by the elastic and plastic shear
properties based on the experimental results. The fully calibrated face sheet material
model reproduces the performed shear test results in terms of both stress-strain relationship and face sheet fracture progression. The corresponding experimental and numerical studies are described in detail in section 5.2.
Summary
The structural element building block concludes with validated elastic constituent material properties of face sheet and core as well as a fully calibrated face sheet material
model including compressive and shear strength properties. Since no fracture of the core