of 5
Supplementary Information:
Insensitivity to Flaws Leads to Damage Tolerance
in Brittle Architected Meta
-­‐
Materials
Authors: Montemayor, L. C., Wong, W. H
.,
Zhang, Y.
-­‐
W., Greer, J. R.
Representative Images of Etched and Non
-­‐
Etched Samples
The samples are imaged at 5
-­‐
10kV to non
-­‐
destructively determine the amount of polymer
that has been removed.
Figure
7
shows a representative sample that shows the location of the
polymer, which is denoted by a change in contrast of the sample. Samples wer
e etched in O
2
plasma
for a total of 16
-­‐
18 hours, depending on the notch length, and checked for hollowness every 4
-­‐
6
hours.
Figure 7:
Representative images of polymer etching using different SEM voltages; the red dotted line indicated the etch front
of the O
2
plasma in the octet
-­‐
truss head
Calculation of Stiffness for Grip and Test Gauge Sections
The strength and stiffness of a stretc
hing
-­‐
dominated cellular solid, such as the octet
-­‐
truss lattice,
scale linearly with the modulus and relative density
, where
is the ratio between the volume of the
lattice unit cell normalized by the total volume occupied by the unit cell
31,48
. These
theories assume
long, slender, solid bars with rigid nodal connections, though many lightweight foams are made with
techniques that produce hollow bars and nodes
43,49,50
. The hollow kagome test sections in this work
have a relative density of
=
0
.
02
and the octet
-­‐
truss grips have a relative density of
=
0
.
38
. The
relative densities are estimated from Solidworks model assuming a constant, perfectly 50nm
conformal coating of Al
2
O
3
and either hollow (kagome test section) or filled (octet
-­‐
truss grips) lattice
tubes. The SolidWorks model assumes a unit cell size of
l
=3. 85
μ
m for the kagome test section and
l
=4.5
μ
m for the octet
-­‐
truss grips. The dimensions of the voxel, which are used to trace the lattice
geometry, have a semi
-­‐
major axis of
a
= 1.8
μ
m and semi
-­‐
minor axis of
b
= 0.5
μ
m.
These voxel
dimensions were d
etermined by measuring the voxel for a variety of laser power settings for the
two
-­‐
photon lithography process.
The relationship between relative density and stiffness of the hollow kagome lattices was
determined using cyclic nano
-­‐
indentation (G200) in the
elastic regime of samples with dimensions of
4x5x3 unit cells in size at a quasi
-­‐
static strain rate of
=
10
!
!
!
!
. The lattice unit cell sizes was
l
=
3.5
μ
m, the wall thicknesses of the Al
2
O
3
coating was 50nm, and the angle of the kagome unit cells was
θ
= 54.7°. The relative density of the hollow kagome nanolattice was determined to be
=
0
.
02
,
similar to those tested in uniaxial tension in this work. Three cycles were used and the modulus is
30!
μ
m!
SEM!Image!at!2!kV!
SEM!Image!at!5!kV!