SAMPE Journal - July/August 2024 - 44

FEATURE / HONEYCOMB STRUCTURES
Figure 7. The performance metrics computed in this study for the unplated and plated HC samples
without BIs (0BI) and with BIs at 50, 75, and 100% of the sample height (0.5BI, 0.75BI and 1.0BI,
respectively). Here, peak values of crush efficiency and energy absorbed efficiency are used.
from spk
=25 MPa (0.50Bi) to spk
= 40 MPa (1.0BI),
but the samples with BIs had a reduced peak stress
compared to the sample without BIs. In contrast,
the plated HC samples exhibited a marked
decrease in the peak stress as the BIs moved up the
sample, from spk
where the measured stress reached 100 MPa. The plated HC samples had a
five-fold increase in specific energy absorption over the unplated samples
(Table 1).
= 63 MPa to spk = 53 MPa (Figure
7a). In addition, the samples with BIs also had a
lower peak stress when compared to the samples
without BIs.
The second metric is the mean crush stress. The
plated samples exhibit a much greater mean crush
stress over a much wider strain range than their
unplated counterparts (Figure 7b).
The peak crush efficiency of each sample was
determined for its own peak stress and the full
strain range per the sample. As shown in Figure
7c, the plated HC samples exhibited a substantial
increase in crush efficiency. The same can be said
for the energy absorbed efficiency (Figure 7d).
Plating the samples increases the energy absorbed
efficiency, however, the increase between the
unplated and plated HC samples is much more
substantial (Figure 7d).
Finally, it is important to assess how the
addition of metal to the SLA honeycomb structure
impacted the energy absorption performance. The
specific energy absorption is used to make this
assessment. For the unplated samples, the energy
absorption was calculated up to the measured
strain range until the sample exhibited nearly
complete brittle failure. For the plated samples, the
energy absorption was calculated up to the strain
3.4 Comparison of Metrics for Plated Samples
To better visualize these results, a radar plot (Figure 8) of the plated samples
is provided using the performance metrics as the individual spokes. This plot
places the metrics along the exterior of the graph, so that the optimal sample
will envelope suboptimal samples. Starting at the topmost spoke, the peak
stress, spk
, is provided ranges from a high value of spk
to a value of spk
= 75 MPa at the interior
= 52 MPa at the exterior, which implies that a lower peak stress
is more optimal. Moving clockwise around Figure 8, the peak strain dependent
crush efficiency, hSD
, is next with efficiency values ranging from hSD
72% being shown. Next, mean crush stress, smc
which ranges from hEA
= 64% up to
, is shown, which ranges from
smc = 48 MPa to 62 MPa, implying that a greater mean crush stress is desirable.
Next, the peak energy absorbed efficiency, hEA
= 43% to
45%. The difference between the peak stress and the mean crush stress, or Ds
= spk
- smc, is the last spoke: a value of 15 MPa used at the origin of the spoke,
and the exterior point has a value of 2 MPa, which implies that a smaller value
is optimal.
As Figure 8 shows, having BIs in the plated HC samples provides better
energy absorption characteristics. Here, the 0BI sample is enveloped in all
metrics with the exception of the mean crush stress. Mean crush stress only
metric where it performs as one of the best two choices. For the presented
metrics, the optimal appears to be the 0.50BI plated HC sample. The only
metric where the 0.50BI plated HC samples is lacking is the peak stress,
however, the mean crush stress is nearly the same as the peak stress for this
sample, so that this sample is the best performing from an energy absorption
perspective and using this value system. Because the peak stress is only slightly
greater than the mean crush stress, both the energy absorbed efficiency and
the crush efficiency are nearly optimal.
44 | SAMPE JOURNAL | JULY AUGUST 2024
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