Inherent carbon fibre stiffening
as seen
in textile reinforced composites
Stepan V. Lomov1, Alexander E. Bogdanovich2,
Ichiro Taketa1,3, Jian Xu1, Ignaas Verpoest1
1Depertment
MTM, Katholieke Universiteit Leuven, Belgium
23Tex
Inc, Cary, NC, USA
3Toray
S.V. Lomov CompTest-2011 Lausanne
Industries, Japan
1
Contents
1. Introduction: The carbon fibre stiffening phenomenon and previously
observed stiffening effects in carbon fibre textile composites
2. Strain measurements during tensile test
3. Stiffening in 3D woven non-crimp carbon/epoxy composites
4. Conclusions
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1. Introduction:
•
•
The carbon fibre stiffening phenomenon
Previously observed stiffening effects in carbon fibre textile
composites
2. Strain measurements during tensile test
3. Stiffening in 3D woven non-crimp carbon/epoxy composites
4. Conclusions
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Inherent stiffening of carbon fibres
First observed:
Curtis, G. J., J. M. Milne
and W. N. Reynolds
(1968). "Non-Hookean
Behaviour of Strong
Carbon Fibres." Nature
220(5171): 1024-1025
20%
increase
E
strain
1%
figure from:
Shioya, M., E. Hayakawa and A. Takaku
(1996). "Non-hookean stress-strain
response and changes in crystallite
orientation of carbon fibres." Journal of
Materials Science 31(17): 4521-4532
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Literature on carbon fibre stiffening
1.
Curtis, G.J., J.M. Milne and W.N. Reynolds, Non-Hookean behaviour of strong carbon fibres, Nature,
1968, 220(5171): 1024-1025.
2.
van Dreumel, W.H.M. and J.L.M. Kamp, Non Hookean behaviour in fibre direction of carbon-fibre
composites and the influence of fibre waviness on the tensile properties, Journal of Composite
Materials, 1977, 11(Oct): 461-469.
3.
Morley, H., A simple strand test for routine fibre strength and modulus evaluation, Composites, 1982,
13(1): 21-23.
4.
Beetz, C.P., Jr., Strain-induced stiffening of carbon fibres, Fibre Science and Technology, 1982, 16: 219229.
5.
Beetz, C.P., Jr. and G.W. Budd, Strain modulation measurements of stiffening effects in carbon fibers,
5
Review of Scientific Instruments, 1983, 54(9): 1222-1226.
6.
Vangerko, H. and A.J. Barker, The stiffness of unidirectionally reinforced CFRP as a function of strain
rate, strain magnitude and temperature, Composites, 1985, 16(1): 19-22.
7.
Ishikawa, T., M. Matsushima and Y. Hayashi, Hardening non-linear behaviour in longitudinal tension of
unidirectional carbon composites, Journal of Materials Science, 1985, 20: 4075-4083.
8.
Hughes, J.D.H., Strength and modulus of current carbon fibres, Carbon, 1986, 24(5):
551-556.
1
1
9.
Stecenko, T.B. and M.M. Stevanovic, Variation of elastic moduli with strain in carbon/epoxy laminates,
Journal of Composite Materials, 1990, 24: 1152-1158.
10.
1960sand
1970s
1980s 1990s 2000s
Northolt, M.G., L.H. Veldhuizen and H. Jansen, Tensile deformation of carbon fibers
the relationship
with the modulus for shear between the basal planes, Carbon, 1991, 29(8): 1267-1279.
11.
Shioya, M and A. Takaku, Rotation and extension of crystallites in carbon fibers by tensile stress,
Carbon, 1994, 32(4): 615-619.
12.
Shioya, M., E. Hayakawa and A. Takaku, Non-hookean stress-strain response and changes in crystallite
orientation of carbon fibres, Journal of Materials Science, 1996, 31(17): 4521-4532.
13.
Toyama, N. and J. Takatsubo, An investigation of non-linear elastic behavior of CFRP laminates and
strain measurement using Lamb waves, Composites Science and Technology, 2004, 64: 2509–2516
S.V. Lomov CompTest-2011 Lausanne
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1
5
Cross-ply carbon laminates: stiffening vs damage
softening
Toyama, N. and J. Takatsubo (2004). "An investigation of non-linear elastic behavior of CFRP
laminates and strain measurement using Lamb waves." Composites Science and Technology
64: 2509–2516.
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Textile composites
Ishikawa, T., M. Matsushima and Y. Hayashi, Hardening non-linear behaviour in
longitudinal tension of unidirectional carbon composites, Journal of
Materials Science, 1985, 20: 4075-4083
Stiffening effect is noted for 8-harness satin – more pronounced effect for
straight fibres
Truong, T. C. . The mechanical performance and damage of multi-axial milti-ply
carbon fabric reinforced composites. PhD thesis, Department MTM. Leuven,
Katholieke Universiteit Leuven, 2005
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Carbon/PP woven composites
+20%
spectacular increase of stiffness …
… may be caused by decrimping as well …
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Carbon/epoxy twill woven composite
stress, MPa
E, GPa
0.2 0.4
0.6
70
60
strain, %
0.2
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0.4
0.6
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1. Introduction: The carbon fibre stiffening phenomenon and previously
observed stiffening effects in carbon fibre textile composites
2. Strain measurements during tensile test
3. Stiffening in 3D woven non-crimp carbon/epoxy composites
4. Conclusions
S.V. Lomov CompTest-2011 Lausanne
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Optical extensometry
0.014
0.012
y = 0.1848x + 0.0059
2
R = 0.9994
LIMESS
eps_X
0.010
0.008
0.006
0.004
2
0.002
y = -4.9477x + 0.6852x
R2 = 0.9996
0.000
0.000
0.010
0.020
0.030
0.040
eps grips
1000
grips
2.
3.
Precise position of zero
of LIMESS curves
Two regions on the
curves
Choice of the fitting
true: LIMESS
800
sig, MPa
1.
600
Instron
400
200
0
0
0.01
0.02
0.03
0.04
0.05
0.06
strain
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1. Introduction: The carbon fibre stiffening phenomenon and previously
observed stiffening effects in carbon fibre textile composites
2. Strain measurements during tensile test
3. Stiffening in 3D woven non-crimp carbon/epoxy composites
4. Conclusions
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The 3D woven non-crimp carbon/epoxy composite
Warp/fill yarns
Toho Tenax 12K, 800
tex
Areal density, g/m2
Z yarns
Toho Tenax 1K, 66 tex
Ends/picks, per inch in layer
12 / 10
Fiber diameter, µm
7*
Fibre Young modulus, GPa
238*
Fibre strength,MPa
3950*
Composite
thickness, mm
2.760.028
Waviness, warp
0.03%
Waviness, fill,
outer/inner
layer
0.08% / 0.02%
2499
Fibre ultimate elongation
1.7%*
Fiber volume fraction in the
composite
51.1%0.5%
Fibre volume fraction, fibres in
warp:fill:vertical directions
Fibre volume fraction inside
warp and fill yarns
24.2%:26.2%:0.7%
61…73%
* datasheet of Toho Tenax
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Expected values of Young’s modulus
Fibre Young modulus, GPa
Fiber volume fraction in the composite
Fibre volume fraction, fibres in
warp:fill:vertical directions
Waviness, warp
Waviness, fill, outer/inner layer
238*
51.1%0.5%
24.2%:26.2%:0.7%
0.03%
0.08% / 0.02%
* datasheet of Toho Tenax
Ewarp  238* 0.242  57.7 GPa  60 GPa
E fill  238* 0.262  62.4 GPa  65 GPa
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Change of Young’s modulus
expected:
Ewarp  238* 0.242  57.7 GPa  60 GPa
1000
100
900
90
800
80
E fill  238* 0.262  62.4 GPa  65 GPa
fill
stress, MPa
70
600
60
warp
500
50
400
40
300
30
200
20
100
10
0
E, GPa
700
expected
0
0
0.005
0.01
0.015
strain
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Change of Young modulus and damage
stress, MPa
E*10, GPa
1000
1.E+08
900
1.E+07
800
1.E+06
700
20% increase of E
600
1.E+05
500
1.E+04
400
1.E+03
AE
300
1.E+02
200
100
1.E+01
0
1.E+00
0.016
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
strain
1000
1.E+08
900
1.E+07
800
1.E+06
700
1.E+05
600
500
1.E+04 AE
400
1.E+03
300
1.E+02
200
100
1.E+01
0
1.E+00
0.016
0
0.002
S.V. Lomov CompTest-2011 Lausanne
0.004
0.006
0.008
0.01
0.012
0.014
16
Impregnated carbon yarns: 6K and 12K
stress – strain:
mixed data for 3K and 12 K
fabric, warp
and fill
6K
12K
Young’s modulus,
normalised
VF = 70%
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Stiffening and fatigue: S-N curve
max
I
warp
900
maximum fatigue stress, MPa
800
stress
1000
II
fill
min
700
time
600
III
500
400
300
200
100
0
1.E+00
WARP static
WARP
WARP no break
FILL static
FILL
FILL no break
Log. (FILL)
Log. (WARP)
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
fatigue cycles
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Post-fatigue tensile test: Fatigue @ 450 MPa,
1,000,000 cycles
800
warp
stress
E
700
80
70
800
80
static @450 MPa
700
fill
70
static @450 MPa
600
60
600
500
50
500
400
40
400
40
300
30
300
30
200
20
200
20
100
10
100
10
strain
0
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
60
initial static
50
strain
0
0.02
0
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0
0.016
quasi-static evolution of Young’s modulus
max
stress
70
E, GPa
65
60
55
min
50
time
0
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200
400
600
stress, MPa
800
1000
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1. Introduction: The carbon fibre stiffening phenomenon and previously
observed stiffening effects in carbon fibre textile composites
2. Strain measurements during tensile test
3. Stiffening in 3D woven non-crimp carbon/epoxy composites
4. Conclusions
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Conclusions: Evolution of Young’s modulus of
carbon/epoxy textile composites
Quasi-static tension:
•
inherent stiffening of carbon
fibres
•
softening of the composite due
to damage
Fatigue and post-fatigue:
•
change of Young modulus in
the first cycles: possible high
modulus
softening due to damage
min
E, warp
65
E, GPa
stress
•
max
time
60
55
0
200
400
600
800
1000
stress, MPa
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