comptest 2011, 14 th february 2011 johannes w g treiber denis d r cartié ivana k partridge...
TRANSCRIPT
CompTest 2011, 14th February 2011 Johannes W G Treiber Denis D R CartiéIvana K Partridge
Effects of mesostructure on the in-plane properties of tufted carbon fabric composites
2/14
Tufting process
- Modified one-sided stitching process
- Automated insertion of carbon, glass or aramid thread
- For dry composite preforms
Hollow needlePresser
foot
Tuft thread loop
Automated KSL KL150 tufting head
Dry fabric
Support foam
0.5% carbon tufted NCF
Bottom
Top
Tufting process
Exp. database Meso-structure FE-Models
3/14
Need for detailed testing database on wider range of tufted materials
Tufting process Exp. database Meso-structure FE-Models
Introduction
Main purpose: Through-the-thickness reinforcement technique
+ 460%/+60% mode I/II delamination toughness
for only 0.5% areal tuft density (Cranfield)
Tufting: - to date only 3 experimental studies (KU Leuven, Cranfield)
Tensile strengths: -14% to +10%
no agreement
Drawback: Potential reduction of in-plane properties
Stitching: - considerable database
Stiffness: -15% to +10% Tensile strength: -25% to +25%
Delamination crack
Tuft bridging
DCB of 0.5% carbon tufted NCF
4/14 Tufting process Exp. database Meso-structure FE-Models
Materials
- Carbon Preforms: Uni-weave - [0°]7 , [0°]10
balanced NCF - [(0°/90°)s]2
- Tufted with 2k HTA carbon thread in at sx = sy = 5.6 mm (0.5%)
/2.8 mm (2%)
- Cross-over
- Pattern shift
Free loop height:
3.5 – 5 mm
- RTM injection of epoxy resin (ACG MVR 444) for dimensional control
Square arrangement
5/14
0.5
0.6
0.7
0.8
0.9
1
1.1
0.0 0.5 1.0 1.5 2.0 2.5
Areal tuft density (%)N
orm
alis
ed s
tren
gth
(-)
UD||
NCF||
UD^
NCF ‘threadless‘
0.9
1
1.1
1.2
1.3
1.4
1.5
0.0 0.5 1.0 1.5 2.0 2.5
Areal tuft density (%)
UD||
Nor
mal
ised
ela
stic
mod
ulus
(-)
NCF||
UD^
Tufting process Exp. database Meso-structure FE-Models
In-plane tension behaviour
Tensile tests (BS EN ISO 527-4:1997):
Property changes depend on fabric and tuft morphology
6/14
Meso-structure
In-plane disturbance (x-y):
Tufting process Exp. database Meso-structure FE-Models
Thread
Loop
Tuft
z
x
y
Resin pocket Tu
ft
Thermal crack
Fabric deviati
on0.5%
UD
NCF
Square
2.0%
Triangular
Square
2φ
w
w,φ
w ,φUD: 6°NCF: 10°
4°
7°
UD: 3°NCF: 4°
7/14
50
55
60
65
70
75
80
0 0.5 1 1.5 2 2.5Distance between tuft rows (mm)
Loca
l fib
re v
olum
e fr
actio
n (%
)
Vf,2D
Meso-structure
Tufting process Exp. database Meso-structure FE-Models
- Surface seam causes local fabric crimp
- Resin rich layers and pockets affect global and local Vf
Out-of-plane disturbance (x-z/y-z):
Surface
crimp
Thread
seam
Loop layer tl
Thread
Loop
Tuft
z
x
y
y
z
x
z
Thread layer tth
Vf = f(wi,tloop, tthread)
8/14
67.5
63.0
Vf (
%)
wde
v
w xy
z
Tufting process Exp. database Meso-structure FE-Models
Numerical Unit Cell model
Parametric 3D Unit Cell model (Marc): UD, NCF, square and triangular arrangement
wi
Vf = f(tl,tth,wi)
¼ UC
Isotropic, linear elastic material + ‘Rule of mixtures’ (Chamis)
Failure and degradation:
0
*
deg67.0
0.1/03.0
nt
n
nt
n
G
E
G
E0* n
Knops, Comp. Sci. Tech. 2006
φ = cosine fct.
Ply: Puck (FF + 3 modes of IFF)
Resin: Maximum strength
Tuft
Resin chann
el‘Smeared’
UD
Loop
Thread
0deg 1.0 EE
x
y x
y
9/14
0
150
300
450
600
750
900
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Experiment
FE Model
Tensile strain ε|| (%)T
ensi
le s
tres
s σ
|| (M
Pa)
90° ply cracking
1.0
0.0
0.5
Shear
Longitudinal splitting
Str
ess
exp
osur
e IF
F σ
n>0
0° Ply
A
Tufting process Exp. database Meso-structure FE-Models
A
- Accurate modulus and strength, also for 2% density (error < 2/4%)
- Fabric straightening leads to transverse tension failure in fabric and longitudinal splitting of resin pocket
Failure prediction – NCF
Transverse
tension failure
Longitudinal splitting
Cracks
Longitudinal splitting
0.5% NCF||
¼ UC
10/14
1.0
0.6
0.8
Str
ess
expo
sure
FF
Initiation of fibre failure
Tufting process Exp. database Meso-structure FE-Models
- Ultimate fabric fibre failure in close vicinity of tuft
B
Failure prediction – NCF
0°
Fibre failure
initiation
Rupture
0
150
300
450
600
750
900
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Experiment
FE Model
Tensile strain ε|| (%)T
ensi
le s
tres
s σ
|| (M
Pa)
B
0° Ply
0.5% NCF||
Tuft
¼ UC
11/14 Tufting process Exp. database Meso-structure FE-Models
Vf distribution
0.5% NCF||
0.80
0.90
1.00
1.10
1.20
ΔVf=f(wi) ΔVf=f(Ar.p.) ΔVf=0
NCF - Modulus
NCF - Strength
Vf distribution models
ΔVf=f(wi) ΔVf=f(Arp) ΔVf=0
Nor
mal
ised
axi
al p
rope
rtie
s (-
)
- Local fabric fibre distribution affects both stiffness and strength prediction
- Gradient Vf model agrees best with true morphology and
tension results
12/14
0.80
0.85
0.90
0.95
1.00
1.05
0 2 4 6 8 10
Modulus
StrengthNor
mal
ised
pro
pert
ies
(-)
Max. Fibre deviation φdev (°)
UDNCF
Tufting process Exp. database Meso-structure FE-Models
Fibre misalignment φ
0.5% square
- Fabric fibre deviation critical on tensile strength, effect on modulus negligible
- UD strength more sensitive to fabric deviation
0°
¼ UC
wmin
13/14
500
1000
1500
2000
2500
0.0 0.5 1.0 1.5 2.0
Model
Experiment
Tensile strain e|| (%)
Ten
sile
str
engt
h S
|| (-
)
Square
Triangular 68%
95%
80%
94%
Tufting process Exp. database Meso-structure FE-Models
Tuft arrangement
UD||
- Upper and lower strength bounds defined by square and triangular pattern
- Triangular pattern causes most critical strength reduction
14/14
• Tuft introduces structural complexity into Z-reinforced composite
• Critical meso-structural tuft defects: resin rich pockets, fibre deviation, matrix cracking and local fibre compaction
• Tufting has no effect on longitudinal tensile stiffness of UD and biaxial NCF composite, but surface loops increase matrix dominated transverse stiffness
• Reduction in longitudinal tensile strength most prominent for UD (<-19%)
• Fibre undulation most critical contributing factor, fibre breakage limited effect on tensile strength
• High quality experimental morphology data allows accurate tensile stiffness and strength prediction of tufted composites
Conclusions