7.2 Phase 1 - Problem analysis
109
tests is relatively slow, there was no need for high speed cameras. The pre-test analysis
was limited to visual inspection and measuring the key geometric dimensions. The posttest analysis was primarily based on visual inspection of a section cut of the specimen.
An image of a section with the identified damage mechanisms is given in Figure 81 a) in
case of the 19 mm configuration. In order to assign the damage mechanisms to the test
progression, the force displacement curve of the reference test is subdivided in five characteristic stages. Images of the specimen exterior in each stage are given in appendix C1.
a)
b)
Figure 81 Identification of mechanical effects in reference test; a) section of specimen after the
test; b) single force displacement curve of FP10-101 with assigned progression stages
A single force displacement curve, which represents the curve progression of all tested
configurations is illustrated in Figure 81 b). Out of the identified damage mechanisms,
all but the core damage can also be observed in the videos of the live observation. Therefore, these mechanical effects can be easily assigned to the test progression. Mapping
the core damage is more difficult, since it cannot be observed from the exterior. However, based on available literature assumptions are made that enable to assign the core
damage with high certainty. The five test progression stages and the corresponding mechanical effects are explained in the following.
Stage ① represents the linear elastic displacement of the undamaged structure.
Stage ② describes the quadratic flattening of the curve due to shear buckling of the
honeycomb cell walls adjacent to the adhesive. In case of honeycomb sandwich inserts
this was reported by several authors as first damage mechanism [Hei09], [Roy14],
[Son08] and it also reflects the expectation, that the core as weakest component experiences damage first. During the tests, no additional damage was visible from the exterior up until this point.
Debonding of adhesive
and face sheet
Shear buckling
of cell walls
Debonding of core
and face sheet
Face
rupture
2
3
3
5
4
4
3
5
Face shear
damage
5
4
5
3
2
1
109
tests is relatively slow, there was no need for high speed cameras. The pre-test analysis
was limited to visual inspection and measuring the key geometric dimensions. The posttest analysis was primarily based on visual inspection of a section cut of the specimen.
An image of a section with the identified damage mechanisms is given in Figure 81 a) in
case of the 19 mm configuration. In order to assign the damage mechanisms to the test
progression, the force displacement curve of the reference test is subdivided in five characteristic stages. Images of the specimen exterior in each stage are given in appendix C1.
a)
b)
Figure 81 Identification of mechanical effects in reference test; a) section of specimen after the
test; b) single force displacement curve of FP10-101 with assigned progression stages
A single force displacement curve, which represents the curve progression of all tested
configurations is illustrated in Figure 81 b). Out of the identified damage mechanisms,
all but the core damage can also be observed in the videos of the live observation. Therefore, these mechanical effects can be easily assigned to the test progression. Mapping
the core damage is more difficult, since it cannot be observed from the exterior. However, based on available literature assumptions are made that enable to assign the core
damage with high certainty. The five test progression stages and the corresponding mechanical effects are explained in the following.
Stage ① represents the linear elastic displacement of the undamaged structure.
Stage ② describes the quadratic flattening of the curve due to shear buckling of the
honeycomb cell walls adjacent to the adhesive. In case of honeycomb sandwich inserts
this was reported by several authors as first damage mechanism [Hei09], [Roy14],
[Son08] and it also reflects the expectation, that the core as weakest component experiences damage first. During the tests, no additional damage was visible from the exterior up until this point.
Debonding of adhesive
and face sheet
Shear buckling
of cell walls
Debonding of core
and face sheet
Face
rupture
2
3
3
5
4
4
3
5
Face shear
damage
5
4
5
3
2
1