Lehigh University

USTC-Lehigh ExchangeSummer 2015

Project Details Investigate the structural properties of the octet-truss lattice material. Literary review to gain basic understanding of how octet-truss handles load Find critical ratio between Euler buckling and plastic yield failure modes Model lattice using SolidWorks CAD software Import model into FEA software COMSOL and conduct finite element compression test 3D-Print models into solid objects Use MTS machine and perform compression test on printed models Compare experimental and simulation results

Critical Ratio (1)

Using values taken from data sheets found online I was able to determine a range of values for

SolidWorks Models were created in SolidWorks by utilizing the Weldments feature 5 cross-sectional profiles were sketched for the 5 different sets of lattices a=0.5mm, a=0.7mm, a=0.9mm, a=1.1mm, and a=1.3mm 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

Predicted Behavior I was able to calculate the force required to initiate Euler buckling and plastic yield for each lattice set. (2) (2)

By comparing these two values for each lattice set I was able to determine what failure mode to expect for each set. These equations predict that all but Set 5 (a=1.3mm) will exhibit Euler buckling Using COMSOL I was able to simulate a compression test for each set then visually determine what failure mode to expect for each set COMSOL simulations give the same results as the equations Only Set 5 (a=1.3mm) was predicted to exhibit plastic yielding

Set 1: COMSOL (a=0.5mm, Front View)

Set 2: Compression Test

Set 3: COMSOL (a=0.9mm, Front View)

Set 3: Compression Test

Set 4: COMSOL (a=1.1mm, Front View)

Set 4: Compression Test

Set 5: COMSOL (a=1.3mm, Front View)

Set 5: Compression Test

Results Comparison From compression test you can see that for Sets 2 and 3 there are several struts that exhibit some Euler buckling. The corner struts on the top and bottom display buckling.From compression test, Sets 4 and 5 do not exhibit Euler buckling but instead exhibit plastic yield/fracture. Horizontal struts stretch in tension and fracture before other struts are able to buckle There are possible sources of error to account for the discrepancy in the predictions and results Material properties (E, yield strength, density) were taken from a data sheet online and not from specific manufacturer 3D-printed structures made of ABS were not smooth and had many imperfections on the struts for each set

Possible Project Improvements Wasted time on hollow, elliptical cross-section octet-truss lattice (2-3 weeks) Guided tutorials for software (COMSOL) 3D-Printer resolution and accuracy Deadlines for specific tasks (make a schedule) Having software in English (Excel, MATLAB) More Chinese language classes

Works CitedL. R. Meza, S. Das, J. R. Grier, Science 3 1322-1326 (2014)V. S. Deshpande, N. A. Fleck, M. F. Ashby, J. Mech. Phys. Solids 13, 17471769 (2001)