128
7 Virtual testing approach for sandwich panel joints
Face sheets
The material properties of bonded face sheet prepregs are not available for the investigated face sheet layup. Yet, the face sheets have been identified as critical for the damage progression of the reference test. In particular, the shear damage initiation of the
upper face sheet at the boundary of potting and core appears to influence the damage
progression in stage ③ of the force displacement curve (see Figure 81 b), p. 109). Therefore, an investigation has been carried out to determine the face sheet material properties (section 4.2). However, on constituent level only tensile tests were performed because the face sheets are very thin making it difficult to perform compressive and shear
tests on unsupported specimens. The tested specimens were removed from a bonded
sandwich panel in order to account for degradation due to sandwich bonding. Based on
the tensile tests, the elastic modulus and tensile strength in both material directions
have been determined (Figure 52, p. 67).
Adhesive/Potting
In Phase 1, no damage of the adhesive has been identified. Therefore, the adhesive is of
secondary concern on constituent level. However, from the literature review it is known
that the material properties of the potting can have a considerable impact on the joint
strength [Bia11]. In case of the demonstration example, there are no mechanical properties available from the manufacturers data sheet of Ureol [Hun04]. Polyurethane adhesives can have a wide range of mechanical properties depending on the chemical composition [Ran02]. Therefore, material properties cannot just be derived from polyurethane adhesives of other manufacturers. As a result of this, the adhesive has been investigated on constituent level based on standard test methods for plastic materials. This
investigation is described in section 4.3. A suitable material model has been implemented and calibrated to represent the experimentally observed material behavior. The
ABAQUS input deck definition of the adhesive material is given in appendix A3.
Insert
Analogous to the adhesive, no damage of the steel insert has been identified in Phase 1.
It is therefore assumed that elastic material parameters are sufficient for the implementation in the final virtual test model. Elastic material parameters of steel can be derived
from standard literature. Therefore, no additional investigation is required for the insert.
Summary
On constituent level a total of three investigations have been defined, each addressing
the material properties of one constituent. The insert has not been further investigated,
since no damage is evident and material properties are readily available. For the Nomex
honeycomb a robust material model has been established and calibrated. Regarding the
face sheets, only the elastic modulus and the tensile strength have been determined and
7 Virtual testing approach for sandwich panel joints
Face sheets
The material properties of bonded face sheet prepregs are not available for the investigated face sheet layup. Yet, the face sheets have been identified as critical for the damage progression of the reference test. In particular, the shear damage initiation of the
upper face sheet at the boundary of potting and core appears to influence the damage
progression in stage ③ of the force displacement curve (see Figure 81 b), p. 109). Therefore, an investigation has been carried out to determine the face sheet material properties (section 4.2). However, on constituent level only tensile tests were performed because the face sheets are very thin making it difficult to perform compressive and shear
tests on unsupported specimens. The tested specimens were removed from a bonded
sandwich panel in order to account for degradation due to sandwich bonding. Based on
the tensile tests, the elastic modulus and tensile strength in both material directions
have been determined (Figure 52, p. 67).
Adhesive/Potting
In Phase 1, no damage of the adhesive has been identified. Therefore, the adhesive is of
secondary concern on constituent level. However, from the literature review it is known
that the material properties of the potting can have a considerable impact on the joint
strength [Bia11]. In case of the demonstration example, there are no mechanical properties available from the manufacturers data sheet of Ureol [Hun04]. Polyurethane adhesives can have a wide range of mechanical properties depending on the chemical composition [Ran02]. Therefore, material properties cannot just be derived from polyurethane adhesives of other manufacturers. As a result of this, the adhesive has been investigated on constituent level based on standard test methods for plastic materials. This
investigation is described in section 4.3. A suitable material model has been implemented and calibrated to represent the experimentally observed material behavior. The
ABAQUS input deck definition of the adhesive material is given in appendix A3.
Insert
Analogous to the adhesive, no damage of the steel insert has been identified in Phase 1.
It is therefore assumed that elastic material parameters are sufficient for the implementation in the final virtual test model. Elastic material parameters of steel can be derived
from standard literature. Therefore, no additional investigation is required for the insert.
Summary
On constituent level a total of three investigations have been defined, each addressing
the material properties of one constituent. The insert has not been further investigated,
since no damage is evident and material properties are readily available. For the Nomex
honeycomb a robust material model has been established and calibrated. Regarding the
face sheets, only the elastic modulus and the tensile strength have been determined and