2. Project Details
o Investigate the structural properties of the octet-truss lattice material.
o Literary review to gain basic understanding of how octet-truss handles load
o Find critical ratio between Euler buckling and plastic yield failure modes
o Model lattice using SolidWorks CAD software
o Import model into FEA software COMSOL and conduct finite element compression test
o 3D-Print models into solid objects
o Use MTS machine and perform compression test on printed models
o Compare experimental and simulation results
3. Critical Ratio
o (1)
o
o Using values taken from data sheets found online I was able to determine a
range of values for
o
sbuckle =
p2
EI
(kl)2
Astrut
® p2
E(
a
l
)2
p2
E(
a
l
)2
=sF.S. Þ (
a
l
)crit. =
1
p
sF.S.
E
(
a
l
)crit.
0.03076 £ (
a
l
)crit. £ 0.05468 Þ 0.4350mm £ a £ 0.7733mm
4. SolidWorks
o Models were created in SolidWorks by utilizing the Weldments feature
o 5 cross-sectional profiles were sketched for the 5 different sets of lattices
o a=0.5mm, a=0.7mm, a=0.9mm, a=1.1mm, and a=1.3mm
o These profiles were then extruded along a 3D sketch and then using a variety
of mirror and cutting features were reduced to the final model shown below
5. Predicted Behavior
o I was able to calculate the force required to initiate Euler buckling and plastic
yield for each lattice set.
o (2) (2)
o By comparing these two values for each lattice set I was able to determine what failure
mode to expect for each set.
o These equations predict that all but Set 5 (a=1.3mm) will exhibit Euler buckling
o Using COMSOL I was able to simulate a compression test for each set then
visually determine what failure mode to expect for each set
o COMSOL simulations give the same results as the equations
o Only Set 5 (a=1.3mm) was predicted to exhibit plastic yielding
PE =
n2
p3
Esa4
4l2
PY = pa2
sY
14. Results Comparison
o From compression test you can see that for Sets 2 and 3 there are several
struts that exhibit some Euler buckling.
o The corner struts on the top and bottom display buckling.
oFrom compression test, Sets 4 and 5 do not exhibit Euler buckling but instead
exhibit plastic yield/fracture.
o Horizontal struts stretch in tension and fracture before other struts are able to buckle
o There are possible sources of error to account for the discrepancy in the
predictions and results
o Material properties (E, yield strength, density) were taken from a data sheet online and not
from specific manufacturer
o 3D-printed structures made of ABS were not smooth and had many imperfections on the
struts for each set
15. Possible Project Improvements
o Wasted time on hollow, elliptical cross-section octet-truss lattice (2-3 weeks)
o Guided tutorials for software (COMSOL)
o 3D-Printer resolution and accuracy
o Deadlines for specific tasks (make a schedule)
o Having software in English (Excel, MATLAB)
o More Chinese language classes
16. Works Cited
1. L. R. Meza, S. Das, J. R. Grier, Science 3 1322-1326 (2014)
2. V. S. Deshpande, N. A. Fleck, M. F. Ashby, J. Mech. Phys. Solids
13, 1747–1769 (2001)
