lyle 20777285 presentation
TRANSCRIPT
SLM Components in CFRP Composite Assemblies
Presented by Lyle Campbell
Supervised by Professor Tim Sercombe
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
Sandwich Structure Response
• Bending
dominant over
large spans
• Shear significant
over short spans
Sandwich panel deflection modes. Adapted from Hexcel (2000)
Cores and SLM
• Layer by layer
additive
manufacturing
• Geometric freedom
• Al12Si
Selective Laser Melting process schematic (Mumtaz and Hopkinson, 2009)
‘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
‘Web’ Core
• Closed cell structure
• Even load distribution
• Higher mechanical
properties
• High stiffness
applications
Schematic of web core section
Failure Modes
• Shear overloading
• Buckling
– Struts
– Webs
– Skins
• Core crush
• De-bonding
Upper; Honeycomb shear wrinkling. Adapted from Bertrand (2006)
Lower; Adhesive filleting at web core-skin interface.
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
Results – 3 Point Bend
0
5
10
15
20
25
30
35
40
45
10% 12% 14% 16% 18% 20% 22% 24%
Sa
mp
le S
tiff
ne
ss
(k
N/m
m)
Solid Fraction (Percentage)
Lattice Measured
Web Measured
Lattice FEM
Web FEM
All error bars show one standard deviation
Results – Shear Modulus
0
1
2
3
4
5
6
7
10% 12% 14% 16% 18% 20% 22% 24%
Sh
ea
r M
od
ulu
s (
GP
a)
Solid Fraction (Percentage)
Web Ideal
Lattice Ideal
Web Short Span
Lattice Short Span
Ideal = 2.8 x short span
Results –Normalised Specific Shear Modulus
0.0
0.5
1.0
1.5
2.0
2.5
Honeycomb 18% Web 21% Lattice Foam
*Normalised w.r.t. honeycomb
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)
Testing
• Lap shear test
• Sandblast & acetone bath
• Adhesive failure
Sandwich Panel Inserts
• Introduce concentrated
loads into panel
– Bending into skins
– Shear into core
Typical ‘cotton reel’ panel insert. Adapted from Shurlock (n.d.)
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.
Testing, Model Verification
Left; Single shear insert test in foam core sandwich panel.
Right; Insert pull-out test in foam core sandwich panel.
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
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.
FSAE Vehicle Upright
• Connects wheel to
suspension system
• High stiffness
requirement
Schematic of UWAM 2014 rear axle unsprung assembly
Design and Modelling
Left; Complete upright core assembly Right; exploded view of upright core assembly
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
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
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
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.
Questions
Mesh Independence - Hex
0.3
0.32
0.34
0.36
0.38
0.4
0.42
0.44
0 5 10 15 20 25 30
De
fle
cti
on
(m
m)
Element Count (Thousands)
Mesh Independence - Tet
0.3
0.32
0.34
0.36
0.38
0.4
0.42
0.44
0 100 200 300 400 500
De
fle
cti
on
(m
m)
Element Count (Thousands)
Tet Deflection
Material Property Testing, Composite FE Model Validation
Results – Shear Strength
0
5
10
15
20
25
30
35
40
10% 12% 14% 16% 18% 20% 22% 24%
Sh
ea
r S
tre
ng
th (
MP
a)
Solid Fraction
Web Measured
Lattice FEM
Lattice Measured
Web FEM
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Honeycomb 14% Web 21% Lattice Foam
Results –Normalised Specific Shear Strength
Results – Compressive Modulus
0
100
200
300
400
500
600
8% 10% 12% 14% 16% 18% 20% 22%
Yo
un
g's
Mo
du
lus (
MP
a)
Solid Fraction
Web
Lattice
Results – Normalised Specific Compressive Modulus
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Honeycomb 10% Web 11% Lattice Foam
Results – Compressive Strength
0
10
20
30
40
50
60
70
8% 10% 12% 14% 16% 18% 20% 22%
Co
mp
ressiv
e S
tren
gth
(M
Pa)
Solid Fraction
Web
Lattice
Results – Normalised Specific Compressive Strength
0.00
0.50
1.00
1.50
2.00
2.50
Honeycomb 18% Web 21% Lattice Foam
SLM Settings, Material Properties
Scan Speed (mm/s) Laser Power (W) Laser Focus (mm)
400 200 4
σy (MPa) σUTS (MPa) Density Elastic Modulus (GPa)
223 ± 11 355 ± 8 97.5 ±0.3 68