NASA LaRC Internship FLOAT Presentation

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Human Landing System
National Aeronautics and
Space Administration
Human Landing System (HLS)
Brian Notosubagyo, Rose Paddock, Jack Steinmetz, Gary Holmgren
Exit Presentation
FLOAT: Footpad Landing Gear
Optimization for Artemis Terrain
13th August 2021

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Footpad Nomenclature
• Baseplate
o Bottom surface of footpad that contacts lunar surface
o Function: Will be taking the majority of the impact force
• Ribs
o Extends outwards from the joint, above the baseplate
o Function: Provides structural support, especially for outer sections
• Outer-lip
o Lateral surface of baseplate
o Function: Protects footpad from obstacles and tipping
• Probe
o Mechanical collapsible feature that extends to lunar surface and signals for
engine shutoff.
o Note: For FLOAT Project, we chose to omit the optimization of the probe
and focused solely on the structural components of the footpad.
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Footpad Nomenclature
Baseplate Ribs Outer-lip
Probe

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Auxetic Metamaterials
• Characteristics
– Negative Poisson’s Ratio
• Improved Impact Resistance
– Synclastic (Dome) Behavior
• FLOAT Footpad Application
– Auxetic Honeycomb Infill of Baseplate for
improved lunar regolith impact resistance
– Potential Weight Savings
• Software/Tools
– Creo Parametric (v4.0 and v7.0)
– Creo Simulate
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Fig 1: Auxetic Bowtie Shell Geomtry1
a) Saddle Shape (Conventional) b) Dome Shape (Auxetic)
Fig 2: Anti-clastic and Synclastic nature of conventional material (a) and auxetic material (b)2
Fig 3: Indentation Behavior1
Fig 4: Auxetic Honeycomb Indentation Behavior3

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Topology Optimization
• Concept
– Iterative mathematical method that
optimizes material layout within a given
design space and specified goal
• FLOAT Footpad Application
– Novel method of weight savings using
generative design
• Software/Tools
– Creo Parametric (v4.0)
– LS-DYNA
– LS-TASC
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3D Printing Fabrication
• Manufacture
– Explore novel method of Footpad
manufacture
– Most feasible way to fabricate auxetic
honeycomb structure
– Intention of using Langley Advanced
Manufacturing capabilities
• FLOAT Footpad Application
– Auxetic Honeycomb Fabrication
– Rapid Prototyping for Test Validation
• Software/Tools
– Creo Parametric (v7.0)
– Ultimaker Cura
– Formlabs Form 3 SLA Printer
– Dremel Digilab 3D45 Printer
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Creo Simulate: Forces and Constraints
Constraints
• Footpads were constrained at the ball joint
and top face of the hub feature.
• This constraint restricted translation in all
directions and allowed for rotation
Forces
• Lunar Gravity: 1/6 Earth’s gravity = 1.63 m/s2
• Vertical Landing: Simplified version, 383kN force applied across entire bottom outer-ring
• Horizontal Impact: Footpad horizontal impact with a 400N force to observe deformation behavior.
o Two Cases: Along “Strong Side” of Cell and Transverse Impact
Vertical Landing Horizontal Impact
Strong Side
Constraint Case
Lunar Gravity
Transverse

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Creo Simulate: Forces Rationale
Vertical Landing
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Horizontal Impact
F=ma → F = (Lunar Gravity + Acceleration Limit)*(Mass)
F = (1.62m/s2 + 19.62m/s2)(18,000kg) = 382,320 N *
Simulation forces: Fvertical = 383 kN Fhorizontal = 0 N
Favg
*=(1/2)mv2→ Favg = (.5)*(Footpa50kgd Mass)*(Footpad Velocity)2
s (Distance between Footpad and Lunar Boulder)
Favg = (.5)*(50kg)*(4m/s)2 = 400 N
(1m)
Simulation forces: Fvertical = 0 kN Fhorizontal = 400 N
Vertical Landing (Reused SuRF Test Case)
• Conservative Estimate: Maximum acceleration, lunar gravity, and lander mass are known: 2 G’s, 1.62 m/s2, 18,000 kg
Horizontal Impact
• Impact Force calculated to stop just the footpad (excluding lander mass) when colliding with lunar boulder to observe deformation behavior
• Variables: Footpad Mass (m) , Footpad Velocity (v, Arbitrarily Chosen), Distance between Footpad and Lunar Boulder (s, Arbitrarily Chosen): 50 kg, 4 m/s, 1 m
* Equation obtained from Engineering Toolbox Reference [4]

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Vertical Landing: Standard Hexagon versus Auxetic Bowtie Honeycomb
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Standard Hexagon Honeycomb Auxetic Bowtie Honeycomb
* Note: Stresses have been scaled up in order to observe behavior

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Horizontal Impact: Stan. Hexagon versus Auxetic Bowtie (Strong Side)
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Standard Hexagon Honeycomb Auxetic Bowtie Honeycomb
Undeformed
Deformed: Hexagon Cell displays
indentation at impact
Undeformed
Deformed: Bowtie Cell demonstrates
slight auxetic behavior (i.e. material
rotates towards impact)
* Note: Deformations have been scaled up 10% in order to observe behavior

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Horizontal Impact: Stan. Hexagon versus Auxetic Bowtie (Transverse)
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Transverse Impact
• No discernable difference in behavior
between honeycomb deformations
3D Lattice Exploration
• Currently examining 2D honeycomb
lattice which can exhibit improved
impact resistance in one direction
• Further models were generated to
explore 3D auxetic pattern that exhibit
more isotropic properties (all directions)
* Note: Deformations have been scaled up 10% in order to
observe behavior

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LS-DYNA Footpad Landing Simulations: Footpad
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• Material properties
• hello
• Laminated composite fabric
• Density = 1.6e-6 kg/mm3
• Young's Modulus = 145 GPa
• Poisson's ratio = 0.25
• Shear Modulus = 0.6 GPa
[11]

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LS-DYNA Footpad Landing Simulations: Lunar Regolith
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• Simulating the moon surface
• hello
• Solid part (non-rigid, not hollow)
• Fully integrated solid
• 1350 x 1350 x 675 mm
• Mesh boxes are 45 mm length
• Mesh 30 x 30 x 15

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LS-DYNA Footpad Landing Simulations: Lunar Regolith
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Low Density
Medium
Density
(Baseline) High Density
Medium Density
(Baseline for
FLOAT Footpad
LS-DYNA Sim)
Density (kg/m3) 1496 1817 1998
1.817E-6
(kg/mm3)
Shear Modulus
(Pa) 5.00E+06 5.00E+06 5.00E+06 5E-3 (GPa)
Poisson's Ratio 0.25 0.25 0.25 0.25
Shear Angle
(rad) 0.6981 0.7000 0.8727 0.7000 (rad)
Shear Angle
(deg) 40.0 40.1 50.0 40.1 (deg)
Cohesive Stress
(Pa) 500 1000 1000 1E-6 (GPa)
• Material Properties
• hello
• Mohr-Coulomb failure criterion
• Greg Vassilakos was generous to
provide information from his analysis
for another lunar module about the
material properties of moon regolith.
(chart below)
• Important: Units!
• hello
• Program runs on numbers, so units need to be decided
internally and remain consistent.
• mm, kg, ms, kN, GPa, kg/mm3

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LS-DYNA Footpad Landing Simulations: Contact and Velocity
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• Specified the two contact
surfaces
• hello
• Slave and master
surfaces: footpad and
ground, respectfully
• Learned later that
whichever I specify as
slave and master
doesn't really affect the
result

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LS-DYNA Footpad Landing Simulations: Contact and Velocity
• Velocity
• hello
• Footpad 800 mm above the
origin (125 mm above the top
surface of the soil block)
• Footpad moving downward
(negative z direction) with an
initial velocity of 3.048 m/s (10
ft/s)
• This was the max allowable
velocity at which Apollo 15
could descend onto the moon.
• Apollo Performance Envelope
10-7-4
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LS-DYNA Footpad Landing Simulations: Vertical Landing
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Von Mises Z Strain
Footpad Bottom View Z strain rings

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LS-DYNA Footpad Landing Simulations: Vert. Landing (Rock Collision)
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Von Mises
Footpad Bottom View
Z Strain

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LS-DYNA Footpad Landing Simulations: 45 Degree Rock Collision
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Von Mises Footpad Bottom View

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LS-DYNA Footpad Landing Simulations: Horizontal Impact
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Initial Velocity Keyword Assignment
Velocity Nodes Displayed Impact Stress

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LS-DYNA Footpad Landing Simulations: Lunar Module Landing
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LS-TASC: Topology Optimization Cases
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Case Selection
• Vertical Landing
o Simplicity of Simulation
o Use of Coarser Mesh
o Least Computational Processing Time
• Case Definition
o Input Keyword File
o Use LS-DYNA MPP solver to run
topology optimization

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LS-TASC: Topology Optimization Part and Iteration Definition
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• Part Definition
o Specify Part ID
o Specify Mass Fraction
• Iteration Definition
o More iterations  Finer Mass
Redistribution
o Limitation: Computer Processing Time

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LS-TASC: Topology Optimization Run
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• Run
o Iterations completed over a week period.
-12 hours per iteration

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LS-TASC: Topology Optimization Results
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Material Utilization
• Interpreting Results
o Similar to Creo Simulate results
o Rib supports and Baseplate material
are integral but can be “shaved”
down
• Topology Optimization Errors
o Unable to view final geometry
o Exported optimized geometry to
LS-Prepost
-No noticeable removal of structure
o Error Possible Explanations:
-Number of Iterations
-Coarser Mesh
Exporting LS-TASC Results
• LS-TASC Export Keyword File LS-
PrePost Save as STL or STEP file
o Blend results with Creo footpad
auxetic honeycomb model
o 3D Print Footpad Prototype

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Auxetic Honeycomb Geometry
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Chiral-Triagonal
Honeycomb
Chiral-Hexagonal
Honeycomb

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CREO Simulate Results
• Auxetic behavior minimizes shear stress
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Additive Manufacturing Geometrical Feasibility and Proof of Concept
• This 30-degree slice of a scaled footpad core section shows how the auxetic chiral honeycomb geometry can be
3D printed without support structures.
• No angle on this geometry exceeds 45-degree overhang making it 3D print friendly.
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NASA LaRC
MakerSpace: Prusa
MK3S Printer

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Trial & Error
• Sometimes you just have to try it!
• Various designs and concepts in
different orientations
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Quarter to visualize scale
Revolved Auxetic pattern

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3D Printed Auxetic Behavior Demonstration
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Chiral-Hexagonal: Uncompressed
Chiral-Triagonal: Uncompressed
Chiral-Hexagonal: Compressed
Chiral-Triagonal: Compressed

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Additive Manufacturing Methods For Functional Prototype
• Utilize 3rd party printing services, or internal use of NASA'S fabrication facilities
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SLS Printing Process FDM Printing Process
SLS Print Render
Composite Print Render
Manufacturing TRL-6, components validated in space
environment
Manufacturing TRL-7, system demonstrated in space
environment

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Alternate (On-Site) Composite Fabrication Options
• Composite ply lower baseplate and upper rib/spoke section
• Utilize ISAAC for advance construction of large surface composite structures, i.e. bottom face of footpad
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ISAAC (Integrated Structural
Assembly of Advanced
Composites)
Manufacturing TRL-5, components validated in
relevant environment
Units: M

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Alternate (On-Site) Composite Fabrication Options
Composite-ply layup process:
MSR-EEV- Courtesy David
Paddock
NASA LaRC Bldg. 1238B/Rm. 110
• FiberSim to CNC for Hand layering composite ply's
in LaRC's composite lab with laser guided CAD
driven placement
Manufacturing TRL-9, mission/flight proven.

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Composite Footpad Shell with Auxetic Printed Core
• 3D printed auxetic core that can be printed in smaller (potentially replaceable) sections
• TRL-3 Analytical critical function/ characteristic proof of concept
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Printed Auxetic Core
Pre-preg Shell

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Future Research
• Experiment with smaller auxetic cells and optimal cell size for
impact resistance
• Create the part in LS-DYNA as a solid mesh part, not shell
• Run finer Footpad mesh for improved Topology Optimization
results.
• Use multiple computers in parallel (MPP) to run
LS-DYNA and LS-TASC simulations
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All files can be found in 2021 Summer Design Project- HLS LG Footpad Teams folder
August 13th – Onward
• Smart material potential to exploit Auxetic characteristics
• Full scale prototype fabrication and testing at LaRC
• Experiment with Auxetic honeycomb infill in Ribs and
Ball Joint structures.
• Produce 3D Printing Fabrication Engineering Drawings
• Perform FEA Analysis on different Auxetic patterns and
materials

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References
• [1] A. Alomarah et al. 2020 Out-of-plane and in-plane compression of additively manufactured auxetic structures
Aerospace Science and Technology 106 (2020) 106107
• [2] A. Boakye et al. 2019 A Review on Auxetic Textile Structures, Their Mechanism and Properties
Journal of Textile Science & Fashion Technology DOI: 10.33552/JTSFT.2019.02.000526
• [3] D. Xiao et al. 2019 The structure response of sandwich beams with metallic auxetic honeycomb cores under localized
impulsive loading-experiments and finite element analysis Materials and Design 176 (2019) 107840
• [4] Impact Force Engineering Toolbox https://www.engineeringtoolbox.com/impact-force-d_1780.html
• [5] Elhaitham Mustafa Elshahat Mustafa_Dynamic Characteristics Study of Re-entrant Honeycomb Auxetic Structure for
Al6082.pdf (bu.edu.eg)
• [6] Slide 1 (gatech.edu)
• [7] Optimization design of chiral hexagonal honeycombs with prescribed elastic properties under large deformation -
ScienceDirect
• [8] Properties of a chiral honeycomb with a poisson's ratio of — 1 - ScienceDirect
• [9] LS-DYNA - Wikipedia
• [10] Online Introduction to LS-DYNA Course | Simulation Innovation and Modeling Center (osu.edu)
• [11] Composites elastic modulus and Poisson ratio | Sonelastic®
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