42
4 Mechanical characterization on constituent level
specimens failed due to tensile core rupture. The results indicate brittle material behavior with linear deformation up until catastrophic failure. This behavior has also been observed by other researchers [Hei08], [Liu15], [Roy14]. There is little to no scatter in terms
of modulus, while the strength showed scatter of 15%.
Transverse shear
The transverse shear test enables to determine the shear modulus and strength parallel
to the sandwich plane. Analogous to the flatwise tensions tests, the specimens were
bonded to loading plates in order to transmit the shear loading, while the relative displacement of the loading plates was measured by an external laser sensor. As with the
previous core tests, transverse shear is a standardized test (ASTM C 273 [AST00] and
DIN 53294 [DIN294]). It should be noted that this test does not produce pure shear.
However, according to the test standards, secondary stresses have minimum effect as
long as the specimen length is sufficient. Since honeycomb cores have two distinct material directions (L and W) the transverse shear tests were performed for both material
directions. In the following, WT and LT refer to transverse shear in L- and W-direction
respectively. Additional test details are summarized in Table 8.
The tests reveal the typical curve progression for Nomex honeycomb transverse shear
tests, confirming previous studies on the same material [Hei08]. For both material directions, the linear elastic deformation is followed by shear buckling of the cell walls which
leads to a considerable drop to a stress plateau. This plateau is held until the cell walls
start to tear, which eventually leads to catastrophic failure. In case of LT-shear, the load
drop due to buckling is more distinct, while the stress plateau ends at considerably lower
strain if compared to WT-shear. The test results along with an image of the test setup
are given in Figure 34. As with the previous tests, the derived transverse shear curves
show little scatter in terms of stiffness, while the strength deviated noticeably (about
10%).
Table 8 Summary of performed transverse shear tests
Test standard
ASTM C 273 [AST00]
Specimen dimension 150 m x 50 mm x 18.5 mm
Loading rate
2 mm/min
Testing machine
Galdabini Quasar 100
Load cell
HBM S9M-10 kN
Disp. measurement
External laser sensor - Micro Epsilon optoNCDT
1630-20
4 Mechanical characterization on constituent level
specimens failed due to tensile core rupture. The results indicate brittle material behavior with linear deformation up until catastrophic failure. This behavior has also been observed by other researchers [Hei08], [Liu15], [Roy14]. There is little to no scatter in terms
of modulus, while the strength showed scatter of 15%.
Transverse shear
The transverse shear test enables to determine the shear modulus and strength parallel
to the sandwich plane. Analogous to the flatwise tensions tests, the specimens were
bonded to loading plates in order to transmit the shear loading, while the relative displacement of the loading plates was measured by an external laser sensor. As with the
previous core tests, transverse shear is a standardized test (ASTM C 273 [AST00] and
DIN 53294 [DIN294]). It should be noted that this test does not produce pure shear.
However, according to the test standards, secondary stresses have minimum effect as
long as the specimen length is sufficient. Since honeycomb cores have two distinct material directions (L and W) the transverse shear tests were performed for both material
directions. In the following, WT and LT refer to transverse shear in L- and W-direction
respectively. Additional test details are summarized in Table 8.
The tests reveal the typical curve progression for Nomex honeycomb transverse shear
tests, confirming previous studies on the same material [Hei08]. For both material directions, the linear elastic deformation is followed by shear buckling of the cell walls which
leads to a considerable drop to a stress plateau. This plateau is held until the cell walls
start to tear, which eventually leads to catastrophic failure. In case of LT-shear, the load
drop due to buckling is more distinct, while the stress plateau ends at considerably lower
strain if compared to WT-shear. The test results along with an image of the test setup
are given in Figure 34. As with the previous tests, the derived transverse shear curves
show little scatter in terms of stiffness, while the strength deviated noticeably (about
10%).
Table 8 Summary of performed transverse shear tests
Test standard
ASTM C 273 [AST00]
Specimen dimension 150 m x 50 mm x 18.5 mm
Loading rate
2 mm/min
Testing machine
Galdabini Quasar 100
Load cell
HBM S9M-10 kN
Disp. measurement
External laser sensor - Micro Epsilon optoNCDT
1630-20