160
8 Development of novel sandwich panel joints
8.2 Validation by experimental investigation
The virtual tests were reproduced in an experimental study. Therefore, the developed
Hourglass and the defined Reference insert were fabricated using a commercial 3Dprinter based on ABS (Designjet Color 3D printer; Hewlett-Packard Development Company, Palo Alto, California). Subsequently, the three investigated design alternatives
were manufactured according to the configuration given in Figure 125. The required cavity for the Undercut design was generated manually using an angled chisel. Three specimens were manufactured for each design. The load introduction into the 3D-printed inserts was implemented by means of SPAX® screws. This proved to be the strongest connection if compared to other options such as threaded inserts for plastics or Heli-Coils®.
All specimens were tested under pull-out loading according to the test parameters given
in Table 24 on page 97. The corresponding test setup is illustrated in Figure 128 in case
of the Hourglass design. Except for the Reference design, the test results are inconsistent
regarding the observed damage patterns and thus the curve progression. This is a result
of premature failure due to insert rupture or screw shearing at high load levels. This failure can be explained by the reduced strength resulting from the non-homogeneous nature of FDM-fabricated parts [Iva13]. In case of the Undercut design, the result variability
is enhanced due to manufacturing inconsistency regarding the shape of the cavity and
thus the potting. A detailed analysis of the test results is given in Appendix C3. Since no
material failure of the insert has been implemented in the virtual tests, the experimental
results indicate lower pull-out strengths than the simulation.
Figure 128 Test setup for experimental study on novel hourglass insert design
Therefore, the experiment test curve with the highest peak force for each alternative
has been selected for comparison with the virtual test results, as these best performing
SPAX®
screw
ABS printed
insert
Pull-out jig
Fixture
8 Development of novel sandwich panel joints
8.2 Validation by experimental investigation
The virtual tests were reproduced in an experimental study. Therefore, the developed
Hourglass and the defined Reference insert were fabricated using a commercial 3Dprinter based on ABS (Designjet Color 3D printer; Hewlett-Packard Development Company, Palo Alto, California). Subsequently, the three investigated design alternatives
were manufactured according to the configuration given in Figure 125. The required cavity for the Undercut design was generated manually using an angled chisel. Three specimens were manufactured for each design. The load introduction into the 3D-printed inserts was implemented by means of SPAX® screws. This proved to be the strongest connection if compared to other options such as threaded inserts for plastics or Heli-Coils®.
All specimens were tested under pull-out loading according to the test parameters given
in Table 24 on page 97. The corresponding test setup is illustrated in Figure 128 in case
of the Hourglass design. Except for the Reference design, the test results are inconsistent
regarding the observed damage patterns and thus the curve progression. This is a result
of premature failure due to insert rupture or screw shearing at high load levels. This failure can be explained by the reduced strength resulting from the non-homogeneous nature of FDM-fabricated parts [Iva13]. In case of the Undercut design, the result variability
is enhanced due to manufacturing inconsistency regarding the shape of the cavity and
thus the potting. A detailed analysis of the test results is given in Appendix C3. Since no
material failure of the insert has been implemented in the virtual tests, the experimental
results indicate lower pull-out strengths than the simulation.
Figure 128 Test setup for experimental study on novel hourglass insert design
Therefore, the experiment test curve with the highest peak force for each alternative
has been selected for comparison with the virtual test results, as these best performing
SPAX®
screw
ABS printed
insert
Pull-out jig
Fixture