Design, Analysis, and Build Preparation of a Bi-stable, Deployable, Lattice Structure
Evan Heatherington
Logan Sharp
Ryan Stebbins
Problem
Literature
Design
Material & Process
FEA
Build Prep
Future Work
[www.3d-profi.de]
[1]
[nustar.caltech.edu]
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Deployable structures have shown to be beneficial for many space, military, and defense applications.
[evajermyn.com]
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Initial research was conducted as to the current, but limited, state of bi-stable lattice configurations.
[1]
[2]
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
The team generated and evaluated many potential solutions to the problem defined.
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Iterative prototypes led to a functional final unit cell design and subsequent volume lattice.
Rapid prototyping done with NinjaTek Cheetah Filament
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Materials for SLA, SLS, and MJF were considered because of their ability to print in polymers with high precision.
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Due to the deployable, bi-stable nature of the lattice unit cell, the following materials were found to be suitable due to their hyper-elastic properties.
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
In order to develop both rapid and end-use prototypes in one of these materials, the following AM printers were determined to be suitable options, but choices will alter the design and process parameters.
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Due to the complexity and required flexibility of the bi-stable lattice, SLS was chosen as the preferred AM technology.
[www.3dsystems.com]
DuraForm Flex
TPU 1301
PA 11
[www.3d-profi.de]
[www.bing.com]
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
EOS TPU 1301 was chosen because of its high elongation and superior mechanical properties compared to DuraForm Flex.
•Great resilience after deformation
•Very good shock absorption
•Very high process stability
•Highly suited to footwear, lifestyle and automotive
•Cushioning elements, protective gears, and shoe soles
Benefits
•Difficult to remove powder from holes
•Not as accurate as PA2200
•Flexibility can vary slightly
•Not good for high stretch applications
Weaknesses
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
EOS P 396 was selected as the desired printer.
EOS P 396
Average price: $303,000
Build Volume: 340 x 340 x 600 mm
Dimensional Accuracy: 120 micron
Minimum Layer Resolution: 60 micron
Minimum Detail Thickness: 0.7mm
Post-Processing: Yes
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Due to the large deformations in this component, non-linear FEA was required. This was performed in SolidWorks using the Blatz-Ko material model.
Where:
µ is the initial shear modulus
and I1,2,3 are invariants of the strain tensor
Blatz-Ko requires minimal input parameter : Elastic Modulus and Tensile Strength
For TPU 3031
E = 60E6 Pa
T.S. = 7Ee6 Pa
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
A prescribed displacement was implemented as the input motion and the bottom of the unit cell was fixed. Simulations mimic prototyped response.
GIF of deformation simulation
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Stresses observed in part are highest in the flexure right before beam buckling demonstrating bi-stability of strain energy.
GIF of stress simulation
Prior to buckling: 1.938E7 Pa
Post- buckling: 1.711E7 Pa
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
A volume lattice was simulated in Fusion 360's cloud finite element solver with a single downward, central force
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Utilizing FEA in nTopology with the unit cell homogenization technique, the stability and stiffness of the unit cell was determined. The upper image shows the deformed unit cell, this validates the desired deflection. ��The image in the lower right visualizes the unit cell's stiffness matrix. This can be used in the future for volume lattice simulation that is not as computationally taxing.
Autodesk Netfabb was used to verify the designed lattices stl files.
[www.3dprint-uk.co.uk]
Good
Bad
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Analysis of the lattices wall thickness was done to ensure the limitations of the EOS P 396 printer was not violated.
Thicker than 0.7mm
Thinner than 0.7mm
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Various part orientations were compared using Netfabb.
Preferred Orientation
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Print time for a 3x3 volume lattice was calculated using Netfabb to be 8hrs 41min.
Scan Speed: 3000 mm/s
Power: 15W
Hatch Spacing: 0.1mm
Layer Height: 0.1 mm
[14]
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
The cost to print was calculated to be $68.43 (87.5 mm cube) 8% the cost of a solid comparable volume.
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
The team's project Gantt Chart is complete justifying the completion of the project
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Future work would involve designing an experiment to validate the optimal process parameters for production. The following L9 Taguchi experiment would test 3 levels of laser power, scan speed, and scan pitch, similar to researchers at Wuhan Polytechnic University [10].
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
Compression testing for plastics would be performed using ASTM D695-15 standard [11]. However, ASTM WK76163 is currently under development for compression testing of lattice structures manufactured through AM [12].
[13]
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
In conclusion, the designed bi-stable lattice structure shows promise for use in deployable structures to increase transportability and reduce costs.
Future Work
Build Prep
FEA
Material & Process
Design
Literature
Problem Description
[nustar.caltech.edu]
References
[1] Alqasimi, A., Lusk, C., & Chimento, J. (2016). Design of a linear bistable compliant crank–slider mechanism. Journal of Mechanisms and Robotics, 8(5). https://doi.org/10.1115/1.4032509
[2] H. Yang and L. Ma, “1D to 3D multi-stable architected materials with zero Poisson's ratio and controllable thermal expansion,” Materials & Design, vol. 188, p. 108430, 2020.
[3] “Duraform Flex (SLS),” 3D Systems, 23-Sep-2021. [Online]. Available: https://www.3dsystems.com/materials/duraform-flex. [Accessed: 15-Sept-2021].
[4] “3D printing elastomers: TPE material for 3D Printers,” 3D Printing Elastomers | TPE Material for 3D Printers. [Online]. Available: https://www.eos.info/en/additive-manufacturing/3d-printing-plastic/sls-polymer-materials/tpe. [Accessed: 15-Sept-2021].
[5] “PA 11 (polyamide 11) for Industrial 3D printing: EOS GmbH,” PA 11 (Polyamide 11) for Industrial 3D Printing | EOS GmbH. [Online]. Available: https://www.eos.info/en/additive-manufacturing/3d-printing-plastic/sls-polymer-materials/pa-11-nylon-abs-pa6. [Accessed: 15-Sept-2021].
[6] “Flexible 80A resin 1 L,” Formlabs. [Online]. Available: https://formlabs.com/store/flexible-80a-resin/. [Accessed: 15-Sept-2021].
References
[7] “F39 white flexible rubber-like 3D printer resin,” RESIONE. [Online]. Available: https://www.resione.com/products/f39-white-flexible-rubber-like-3d-printer-resin-1kg-1. [Accessed: 16-Sept-2021].
[8] “Cheetah 3D printer filament (95A),” NinjaTek, 12-Apr-2021. [Online]. Available: https://ninjatek.com/shop/cheetah/. [Accessed: 16-Sept-2021].
[9] “HP 3D Printing materials portfolio - expand your capabilities,” HP 3D Printing Materials Portfolio - Expand your capabilities | HP® Official Site. [Online]. Available: https://www.hp.com/us-en/printers/3d-printers/materials.html#section=3d-materials-properties. [Accessed: 16-Sept-2021].
[10] G. Hou, H. Zhu, and D. Xie, “The influence of SLS process parameters on the tensile strength of pa2200 powder,” IOP Conference Series: Earth and Environmental Science, vol. 571, no. 1, p. 012111, 2020.
[11] “Standard test method for compressive properties of rigid plastics,” ASTM International - Standards Worldwide. [Online]. Available: https://www.astm.org/d0695-15.html. [Accessed: 29-Nov-2021].
[12] “WK76163 new test method for additive manufacturing -- test artifacts -- compression validation coupons for lattice designs,” ASTM International - Standards Worldwide. [Online]. Available: https://www.astm.org/workitem-wk76163#. [Accessed: 03-Dec-2021].
[13] A. Kumar, S. Verma, and J.-Y. Jeng, “Supportless lattice structures for energy absorption fabricated by fused deposition modeling,” 3D Printing and Additive Manufacturing, vol. 7, no. 2, pp. 85–96, 2020.
[14] S. Yuan, “Development and optimization of selective laser sintered ‑ composites and structures for functional applications,” Nanyang Technological University, 2018.