Rapid Optimization of Composites - HyperSizer Express and FEA
Lyle 20777285 Presentation
1. SLM Components in CFRP
Composite Assemblies
Presented by Lyle Campbell
Supervised by Professor Tim Sercombe
2. Project Purpose
• Develop SLM cores
• Out-perform current
methods
• Construct and test
FRP assemblies
with SLM
components
SLM core assembly of upright
developed in this work
3. Sandwich Structure Response
• Bending
dominant over
large spans
• Shear significant
over short spans
Sandwich panel deflection modes.
Adapted from Hexcel (2000)
4. Cores and SLM
• Layer by layer
additive
manufacturing
• Geometric freedom
• Al12Si
Selective Laser Melting process schematic
(Mumtaz and Hopkinson, 2009)
5. ‘Shear Lattice’ Core
• Align material along
principal directions
• High shear, low
axial properties
• Low solid fraction
applications, <10%
Illustration of shear lattice unit cell
with two major shear planes depicted
6. ‘Web’ Core
• Closed cell structure
• Even load distribution
• Higher mechanical
properties
• High stiffness
applications
Schematic of web core section
8. Modelling and Testing
• ASTM 273 not
possible
• Short span 3
point bend
• HyperMesh 12.0
Upper; 3 point bend test set-up
Lower; Half symmetry 3 point
bend FE model
9. Results – 3 Point Bend
0
5
10
15
20
25
30
35
40
45
10% 12% 14% 16% 18% 20% 22% 24%
SampleStiffness(kN/mm)
Solid Fraction (Percentage)
Lattice Measured
Web Measured
Lattice FEM
Web FEM
All error bars show one
standard deviation
10. Results – Shear Modulus
0
1
2
3
4
5
6
7
10% 12% 14% 16% 18% 20% 22% 24%
ShearModulus(GPa)
Solid Fraction (Percentage)
Web Ideal
Lattice Ideal
Web Short Span
Lattice Short Span
Ideal = 2.8 x short span
12. Joining Cores
• Bolted joint
• Tapered
interference fit
• Mechanical
interlocking with
adhesive
– Grid of rectangular
tongue and slot Illustration of similar joint.
Adapted from Décor Arts Now (2014)
14. Sandwich Panel Inserts
• Introduce concentrated
loads into panel
– Bending into skins
– Shear into core
Typical ‘cotton reel’ panel insert.
Adapted from Shurlock (n.d.)
15. Insert Design
• Avoid large
modulus step
changes
• Smooth deflection
profile
• Tapered density
SLM inserts
Upper; UWAM high load insert
design. Adapted from Bertrand
(2006)
Lower; Illustration of shear deflection profile
around insert.
16. Testing, Model Verification
Left; Single shear insert test in
foam core sandwich panel.
Right; Insert pull-out test in foam
core sandwich panel.
17. Insert Density Study
• Lattice properties varied
and effects examined
• Design requires balance
depending on design
constraints
– Insert mass, diameter
– Skin peak stress
– Bulk core peak stress
Plot of major principal stress illustrating
stress concentrations at insert-core junctions
18. Final Insert Design
• Cubic profile for tapered
stiffness profile on ‘top hat’
• Female thread
• Core properties reduce
radially
• Lattice stiffness compromise
• 25g, 45% of equivalent CF
stack
Cross section view of panel insert designed
for pull-out and single shear. 60 mm OD.
19. FSAE Vehicle Upright
• Connects wheel to
suspension system
• High stiffness
requirement
Schematic of UWAM 2014 rear axle unsprung
assembly
21. Testing and Results
• Modelled in HyperMesh
• Physical testing and
stiffness comparison
• 20% Discrepancy
– Manufacturing errors
– Simplified FEM
geometry
– Tetrahedral elements &
mesh density
• 0.05 degrees/g, 800 grams,
first design iteration
Cross section through upright testing assembly
22. Outcomes and Conclusions
• Developed core structures that outperform current core materials
used by UWAM
• Developed methods for assembling core structures into larger
components
• Developed sandwich panel inserts which improve on current
UWAM design
• Developed composite upright suitable for further testing on a
vehicle
• Developed requisite manufacturing techniques and modelling
methods for the above components
23. Future Work
• Small feature build quality
• Surface finish improvement
• Strength and failure modes,
axial loading
• Fatigue
• Compare wider variety of
cores
• Thermal modelling of inserts
• Energy absorption
• Modelling of adhesive layer
24. Presentation References and
Sources
• Hexcel Composites, 2000. Honeycomb Sandwich Design Technology, s.l.:
Hexcel Composites.
• Hopkinson, N and Mumtz, K, 2009 Selective laser melting of thin wall parts
using pulse shaping. Journal of Materials Processing Technology, Volume 210,
pp. 279-287.
• Bertrand, A., 2007. Composite Chassis Construction for the 2006 UWAM
FSAE Car, s.l.: University of Western Australia.
• Shur-Lok, n.d. Fasteners for Sandwich Structure Catalog. [Online]
[Accessed May 2014].
• European Corporation for Space Standardisation, 2011. Space Engineering;
Insert Design Handbook. Noordwijk: European Space Agency.
• Cote, F., Deshpande, V. & Fleck, N., 2006. The Shear Response of Metallic
Square Honeycombs. Journal of Mechanics of Materials and Structures, 1(7),
pp. 1281-1299.
Composite materials have a large number of possible failure modes. Modes directly related to the core were assessed to ensure components would not fail.
Simple analytical models and large safety margins were used. Margins were easy to accommodate as high stiffness requires low stress anyway.
Failure in the test specimens was always core shear failure.
