4.1 Sandwich core
59
The resin corner approach on the other hand is characterized by a considerably thinner
layer of resin coat. Shear failure of this layer only results in a minor peak in the stressstain relationship. With the damage of the structure progressing, the resin corners eventually fail locally along with cell wall folding due to shear buckling. This local failure of
the resin corner elements is depicted in Figure 47 in case of compression loading. In general, the resin corner approach approximates the experimental stress-strain curve well
for both considered shear directions. In addition, the two investigated hexagon geometries lead to comparable results in case of transverse shear.
Figure 47 Failure of resin corner elements under compression loading at strain = 0.04 [See17]
4.1.4 Numerical modelling with 3D-contiuum elements
As established in section 2.3.1, 3D-continuum elements are generally also capable to
model out-of-plane core damage mechanisms, while at the same time requiring less
modelling and computational effort if compared to detailed meso-scale models. In applications where core damage is only of secondary interest, this simplified modelling approach might be the preferred choice. Therefore, a homogenized core model is derived
and calibrated using the experimental results. This is done using a single element of the
C3D8R type, which is subjected to the four loading conditions compression, tension and
both transverse shear directions (Figure 48). The boundary conditions of the model are
defined analogous to the previous meso scale model (Figure 35), except that no symmetry planes are defined. As material, a generic orthotropic elasto-plastic material
model suitable for 3D-continuum elements is implemented. One of the advantages of
this approach is that material properties given by manufacturers or macroscopic tests,
such as summarized in Table 9 on page 44, can be directly implemented in the material
59
The resin corner approach on the other hand is characterized by a considerably thinner
layer of resin coat. Shear failure of this layer only results in a minor peak in the stressstain relationship. With the damage of the structure progressing, the resin corners eventually fail locally along with cell wall folding due to shear buckling. This local failure of
the resin corner elements is depicted in Figure 47 in case of compression loading. In general, the resin corner approach approximates the experimental stress-strain curve well
for both considered shear directions. In addition, the two investigated hexagon geometries lead to comparable results in case of transverse shear.
Figure 47 Failure of resin corner elements under compression loading at strain = 0.04 [See17]
4.1.4 Numerical modelling with 3D-contiuum elements
As established in section 2.3.1, 3D-continuum elements are generally also capable to
model out-of-plane core damage mechanisms, while at the same time requiring less
modelling and computational effort if compared to detailed meso-scale models. In applications where core damage is only of secondary interest, this simplified modelling approach might be the preferred choice. Therefore, a homogenized core model is derived
and calibrated using the experimental results. This is done using a single element of the
C3D8R type, which is subjected to the four loading conditions compression, tension and
both transverse shear directions (Figure 48). The boundary conditions of the model are
defined analogous to the previous meso scale model (Figure 35), except that no symmetry planes are defined. As material, a generic orthotropic elasto-plastic material
model suitable for 3D-continuum elements is implemented. One of the advantages of
this approach is that material properties given by manufacturers or macroscopic tests,
such as summarized in Table 9 on page 44, can be directly implemented in the material