SAMPE Journal - July/August 2024 - 41

better energy absorption characteristics. There is a
linear elastic region where the initial stress is being
loaded, prior to the progressive collapse region
that occurs between 10 and 60% strain, at which
point densification initiates (Figure 2). The plated
HC samples are able to withstand a significantly
wider strain range (about a seven times greater
strain range) at slightly higher loads. The plated
HC samples are shown to hold peak load closer to
70 MPa. Plating the samples results in over a 25%
increase in the peak stress and 600% increase in
strain range.
(a) Unplated HC
samples
3.2 Effects of Buckling Initiators
As discussed in the previous section, the plated HC
samples indicated the potential to be used in energy
absorbing structures. A study was conducted to
observe the effects of BIs in the performance of both
unplated and plated HC samples. BIs, sometimes
called stress concentrators, are introduced to the
honeycomb structure to encourage folding in a
predictable way. In this study, BIs were placed in
three locations: 50, 75, and 100% the height of the
HC sample, denoted as 0.50BI, 0.75BI and 1.0 BI
samples, respectively, in order to assess BI location
on energy absorption. HC samples with no BIs,
denoted as 0BI samples, were also fabricated for
comparison.
Figure 3 shows the performance of the unplated
and plated HC samples with BIs. The unplated HC
samples exhibit a peak stress of spk
= 56 MPa, and
exhibit brittle failure, and can no longer carry
any significant stress for strain levels above 1020%
(Figure 3a). This low strain range over which
compressive stress can be supported greatly
reduces their energy absorption capacity. The
0BI plated HC samples exhibit a peak stress of spk
=70 MPa and a mean crush stress of smc
= 55 MPa,
while the 0.50BI samples average a peak stress of
spk
=63 MPa and a mean crush stress of smc
= 60
MPa (Figure 3b). To help determine the energy
absorption of these materials, the change in stress
is calculated using Ds = spk
- smc. This quantifies the
difference between the maximum reported value
in the linear elastic range and the average stress
across the entire strain range. Here, a lower value
is better, since it would indicate the peak stress is
equilibrated with the mean crush stress, so that the
crush efficiency would increase.
As the buckling initiator continues to move
vertically up the wall of the plated HC samples,
the overall energy absorption capabilities remains
relatively unchanged. The 0.75BI samples exhibits
a noted decrease in the peak stress, down to spk
58
MPa, however the mean crush stress also decreases
at the same time, to smc
change in stress of about 6 MPa, which is less than
the 0.50 sample. A similar trend occurs with the
1.0BI samples, where the peak stress is about spk
53 MPa, but the mean crush continued to decrease
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= 52 MPa. This is results in a
Yes
0.75 34.94 58.07 52.11 65.62 43.74
1.0 35.10 53.74 49.81 67.80 44.66
1 Peak values are quoted in this column.
JULY AUGUST 2024
|
SAMPE JOURNAL |
41
Table 1. Performance metrics of samples.
Plating
BI W spk
0.0
No
13.11
smc
hSD
1
[g] [MPa] [MPa] [%]
54.54 29.51
hEA
54.11
0.50 12.64 24.86 11.77 47.36
1
SEA
0.75 13.32 34.53 18.84 54.56 2.50
1.0
[%] [MJ/kg]
246.7
56.48
71.37
5.88
2.77
13.01 40.32 25.80 63.97 14.05 441.4
0.0 43.38 70.02 56.24 68.97 43.07 853.7
0.50 40.72 63.55 60.18 71.61
44.21
873.7
1277
1192
Figure 3. Stress vs. strain for the unplated and plated samples with no
buckling initiators (0BI), and with BIs at 50, 75, and 100% of the sample
height (0.50BI, 0.75BI and 1.0BI, respectively).
(b) Plated HC
samples
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SAMPE Journal - July/August 2024

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