CompTest2015,8th‐10th April2015
Exploringtheinfluenceofmicro‐structureon
the mechanical properties and crack bridging
themechanicalpropertiesandcrackbridging
mechanismsoffibroustufts
CamillaOsmiani,Galal Mohamed
Gi li
Giuliano
All i*,IvanaK.Partridge
Allegri
I
K P t id
[email protected]
*Department
of Aeronautics, Imperial College, London
www.bris.ac.uk/composites
TuftingfacilitiesatBristol,UK
Research project carried out in collaboration with
National Composites Centre (NCC) and supported
by Rolls
Rolls-Royce
Royce and EPSRC.
Tufting robot
2/17
3/17
Tufting
• Through-thickness reinforcement (TTR) technique
• Dry preform – liquid resin moulding
• Carbon, glass, aramid threads
• One side access
Composite
[1]
Thread seams
Tuft
Loop
X-ray of a carbon tuft in 8 mm
thi k carbon
thick
b fibre
fib composite
it
[2]
Tufting
f g pprocess
[1] J.W.G. Treiber, PhD Thesis, Cranfield Uni., 2011
Multi‐ScaleModellingApproach
Tuft geometry and equivalent properties identification
Meso-scale model of tufting thread
Unit cell model (single-tuft coupon)
Macro-scale model (DCB, ELS, etc.)
GITuft
Displacement
GITuft
Separation
Unit cell model → Bridging law
Unit-cell
Tractiion
Composite
Tractiion
Stress
Tufting thread
•
•
•
•
4/17
GILaminate
Separation
Macro scale model
Macro-scale
Multi‐ScaleModellingApproach
Tuft geometry and equivalent properties identification
Meso-scale model of tufting thread
Unit cell model (single-tuft coupon)
Macro-scale model (DCB, ELS, etc.)
GITuft
Displacement
GITuft
Separation
Unit cell model → Bridging law
Unit-cell
Tractiion
Composite
Tractiion
Stress
Tufting thread
•
•
•
•
5/17
GILaminate
Separation
Macro scale model
Macro-scale
Multi‐ScaleModellingApproach
Tuft geometry and equivalent properties identification
Meso-scale model of tufting thread
Unit cell model (single-tuft coupon)
Macro-scale model (DCB, ELS, etc.)
GITuft
Displacement
GITuft
Separation
Unit cell model → Bridging law
Unit-cell
Tractiion
Composite
Tractiion
Stress
Tufting thread
•
•
•
•
6/17
GILaminate
Separation
Macro scale model
Macro-scale
Multi‐ScaleModellingApproach
Tuft geometry and equivalent properties identification
Meso-scale model of tufting thread
Unit cell model (single-tuft coupon)
Macro-scale model (DCB, ELS, etc.)
GITuft
Displacement
GITuft
Separation
Unit cell model → Bridging law
Unit-cell
Tractiion
Composite
Tractiion
Stress
Tufting thread
•
•
•
•
7/17
GILaminate
Separation
Macro scale model
Macro-scale
Multi‐ScaleModellingApproach
Tufting thread
•
•
•
•
Tuft geometry and equivalent properties identification
Meso-scale model of tufting thread
Unit cell model (single-tuft coupon)
Macro-scale model (DCB, ELS, etc.)
• Previous investigations at the unit-cell level revealed that
•
8/17
the bridging
th
b id i law
l off the
th tuft
t ft in
i mode
d I is
i highly
hi hl sensitive
iti to
t
the axial stiffness of the tuft, Ez, and the friction stress, τ,
at the tuft-composite interface;
Experimental assessment of Ez and τ necessary for
prediction of toughness enhancement provided by the tuft.
Which parameters influence the elastic
response of the tuft?
9/17
TuftCharacterisation
Focus on meso-scale
meso scale problem:
• Mode I delamination
• Tensile behaviour of tufting thread
i its
in
i impregnated
i
d state
3 mm
CT-scan image of glass
tuft in 10 mm thick
composite
Thread Structure and Properties
Helical interlaced yarns
Twist level (helix pitch, p)
Yarn
Helix radius, r = f (ry , Ny)
Helix lay angle, α = atan(2πr/p)
Yarn linear weight, WL
Yarn dryy cross-section,, Adry = WL/ρρfibre
Threead
•
•
•
•
•
•
p
α
ℓhelix
h li
2πr
10/17
TuftCharacterisation
Thread – Tenax-J HTA40 H15 67tex 15S
Impregnated
thread
• Single carbon yarn
WL = 67 g/km, Adry = 0.038 mm2
• 2-yarn carbon thread
WL = 2x67
2 67 g/km,
/k Adry = 0.076
0 076 mm2, S 215 ttwist/m,
i t/
p = 5.1 mm
0.5 mm/min
250 mm
Resin – Momentive RIMR 935/RIMH 936
• Epoxy resin
• Cure cycle: 2h at 60° + 1.5h at 80°
Tuft
Tensile test configuration
11/17
ExperimentalResults
Impregnated Thread
• Thread architecture influences
mechanical performance
• Ath, impr = 0.11 mm2, Vf = 70%,
E = 186 ± 4MPa
r = 0.13 mm
E = 200 ± 3MPa
Ath,impr
100 μm
Representative stress-strain curves
obtained ffrom tensile tests. Fibres onlyy
assumed to carry the load (ASTM D2343-09)
Micrographs of impregnated single yarn
and 2-yarn thread
12/17
ModelDevelopment
• Continuous method [3] → meso-scale model
• RVE → gauge length = 1 pitch length
• Periodic boundary conditions
• Periodic microstructure material model [4]
ux = uy = 0
uz = εmax p
• Resin pocket in between yarns neglected
z
y
r
x
p
Top
Ath,impr
hi
2
Ath,impr = 0.11 mm2
r = 0.13 mm
[3] A. Gasser et al., Comp. Mat. Sci. 17, 2000
ux = uy = uz = 0
B
Bottom
13/17
ModelDevelopment
• Continuous method [3] → meso-scale model
• RVE → gauge length = 1 pitch length
Resin
i rich
i h
region
Impregnated
yarn
• Periodic boundary conditions
• Periodic microstructure material model [4]
• Resin pocket in between yarns neglected
3
Ef = 200 GPa νf = 0.2
Em = 2.8 GPa νm = 0.4
Vf
%
70
E1
E3
GPa GPa
16
ν12
-
ν13
-
3
G12 G13
GPa GPa
141 0.48 0.03
3
6
5
Transverse isotropy assumed
[3] A. Gasser et al., Comp. Mat. Sci. 17, 2000
3
3
1
1
1
1
1
Material
Orientation
14/17
NumericalResults
x
E = 186 ± 4 MPa
E = 177 MPa
Comparison between numerical and experimental
results
lt for
f the
th 2-yarn
2
carbon
b thread
th d
z
3
3
3
Stress distribution along interlaced
h li l yarns in
helical
i the
h FE model
d l
15/17
SensitivityAnalysis
• How
H ddoes a variation
i ti off the
th helix
h li pitch
it h (p)
( ) influence
i fl
results?
lt ?
pa = 4 mm → αa = 11.5°
pb = 5.1 mm → αb = 9°
Tuft
p
α
Ez,thread
pc = 6 mm → αc = 7.8°
Conclusions&FutureWork
• The present study represents the first milestone in the development
of a multi-scale modelling framework for tufted composites.
• Thread architecture has influence on mechanical performance;
• More accurate results are expected with incorporation of resin
pocket in numerical model;
• Stress distribution in yarn is sensitive to local material orientation;
• Any scale-up modelling procedure should account for the effect of
the helical shape on stress distribution;
16/17
Conclusions&FutureWork
• The present study represents the first milestone in the development
of a multi-scale modelling framework for tufted composites.
• Thread architecture has influence on mechanical performance;
• More accurate results are expected with incorporation of resin
pocket in numerical model;
• Stress distribution in yarn is sensitive to local material orientation;
• Any scale-up modelling procedure should account for the effect of
the helical shape on stress distribution;
Thank you
17/17