4.1 Sandwich core
51
strain relationship in tension/compression. The homogenized density of the cell wall material is defined to match the nominal honeycomb density of the tested specimens (48
kg/m³). The cell wall thicknesses t single and t double are defined based on the previous microscopic measurements (Table 5), while the total wall thickness including the resin coating is considered.
Single layer orthotropic approach
In contrast to the previous isotropic material, the orthotropic material model enables
independent definition of shear modulus and strength as well as tensile and compressive
strength. Hence, it requires the definition of additional material properties. The calibrated material parameters are given Table 10 (right). The uniaxial stress strain relationship of the material is plotted in Figure 40 b). The implemented material is characterized
by slight orthotropy, which represents the orthotropic nature of Nomex with different
material behavior in machine (MD) and cross machine direction (XD) of the base material
(see section 2.1.2). The calibrated elastic properties are in the range of the reviewed
literature [Hei08a], [Roy13], while little reference is available for the strength properties.
Analogous to the single layer isotropic approach, the implemented material behaves perfectly plastic. The wall thicknesses and material density are defined identical to the isotropic approach.
Table 10 Calibrated homogenized material properties for single layer approaches
Single Layer Isotropic
Single Layer Orthotropic
Eiso 4000 MPa
tsingle
0.057 mm
E1
5000 MPa
δ1t
90 MPa
ηiso 0.3
tdouble 0.110 mm
E2
4000 MPa
δ1c
105 MPa
δiso 90 MPa
ρ
1.1 g/cc
G12
1450 MPa
δ2t
60 MPa
ηorth
0.2
δ2c
90 MPa
t single
0.110 mm
δ12
44 MPa
t double 0.057 mm
ρ
1.1 g/cc
Figure 40 Stress-strain relationship for single layer a) isotropic and b) orthotropic material models
51
strain relationship in tension/compression. The homogenized density of the cell wall material is defined to match the nominal honeycomb density of the tested specimens (48
kg/m³). The cell wall thicknesses t single and t double are defined based on the previous microscopic measurements (Table 5), while the total wall thickness including the resin coating is considered.
Single layer orthotropic approach
In contrast to the previous isotropic material, the orthotropic material model enables
independent definition of shear modulus and strength as well as tensile and compressive
strength. Hence, it requires the definition of additional material properties. The calibrated material parameters are given Table 10 (right). The uniaxial stress strain relationship of the material is plotted in Figure 40 b). The implemented material is characterized
by slight orthotropy, which represents the orthotropic nature of Nomex with different
material behavior in machine (MD) and cross machine direction (XD) of the base material
(see section 2.1.2). The calibrated elastic properties are in the range of the reviewed
literature [Hei08a], [Roy13], while little reference is available for the strength properties.
Analogous to the single layer isotropic approach, the implemented material behaves perfectly plastic. The wall thicknesses and material density are defined identical to the isotropic approach.
Table 10 Calibrated homogenized material properties for single layer approaches
Single Layer Isotropic
Single Layer Orthotropic
Eiso 4000 MPa
tsingle
0.057 mm
E1
5000 MPa
δ1t
90 MPa
ηiso 0.3
tdouble 0.110 mm
E2
4000 MPa
δ1c
105 MPa
δiso 90 MPa
ρ
1.1 g/cc
G12
1450 MPa
δ2t
60 MPa
ηorth
0.2
δ2c
90 MPa
t single
0.110 mm
δ12
44 MPa
t double 0.057 mm
ρ
1.1 g/cc
Figure 40 Stress-strain relationship for single layer a) isotropic and b) orthotropic material models