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Through-the-Thickness Mechanical Properties
of Smart Composite Laminates
Gang Zhou, L.M. Sim, P.A. Brewster and A.R. Giles
Department of Aeronautical and Automotive Engineering,
Loughborough University,
Loughborough, Leicestershire LE11 3TU, UKInternational Conference on Composites Testing and
Model Identification
28th January 2003
Background and Motivation
• Smart composite structures: sensory and adaptive
– Sensory smart structures can monitor structural
environment or detect and assess damage
– Adaptive smart structures can modify/control the host structural behaviour
• Embedded optical fibres/SMA wires affect short-term
through-the-thickness mechanical properties?• Facilitate the design of smart structures
2
3
EFPI sensor
Micrograph showing embedded OF
4
• Whether or not defects associated with embedded OFs/SMA wires affect ttt mechanical propertiesifif?
• Under what conditions will these properties be affectedthresholdsthresholds?
• How are these properties be affected how how muchmuch?
Objectives
5
Focal Points of Current Investigation:
• Optical fibres: OrientationNumber/volume fractionThrough-the-depth
locationStress concentration
effect• SMA wires:
Number/volume fraction
6
Through-the-thickness mechanical properties and experimental techniques
• Interlaminar shear (ILS) propertiesShort beam shear (SBS) methodIosipescu shear method
• Flexure Three-point bending
Four-point bending
7
Specimen Manufacturing
• Beam specimensBeam specimens• Acrylate-coated single mode OF of 0.25 mm dia. (OC)• Nitinol wire of 0.5 mm dia. (M-M)• T700/LTM45-EL carbon/epoxy prepreg (ACG)• Autoclave with a single-cycle cure at 600 C
– EFPI sensors are cured at 650 C– Austenitic completion temperature of SMA wires
is about 700 C
• Iosipescu ILS specimensIosipescu ILS specimens: two 900 notches
8
Micrographs showing embedded OFs
9
Micrograph showing embedded OFs
10
Micrograph showing embedded nitinol wires
11
Orientation and through-the-depth location
12
Arrangement of OFs in the transverse direction
13
Through-the-depth location of OFs in Iosipescu shear specimens
14
ILS shear strength via SBS methodOFs in the longitudinal direction
OFs in the transverse direction
0
10
20
30
40
50
60
70
80
Number of optical fibres
Inte
rlam
inar
sh
ear
stre
ng
th (
MP
a)
M 61.63 64.12 59.53
Q 61.63 60.33 63.98 56.21 60.80
Intact 1 OF 2 OFs 3 OFs 5 OFs0
10
20
30
40
50
60
70
80
Number of optical fibres
Inte
rlam
inar
sh
ear
stre
ng
th (
MP
a)C 61.63 58.15 61.03 59.56
O-C 61.63 61.93 62.61 58.01
Intact 1 OF 2 OFs 3 OFs 4 OFs 6 OFs
Table 4 Table 5
15
ILS shear properties via Iosipescu method with OFs in the transverse direction
0
10
20
30
40
50
60
70
80
90
Position of optical fibres
Inte
rlam
inar
sh
ear
stre
ng
th (
MP
a)
ILSS 65.08 66.17 69.50
Intact Mid-plane Quarter0
1
2
3
4
5
6
7
8
Position of optical fibres
Inte
rlam
inar
sh
ear
mo
ud
ulu
s (G
Pa)
ILS Mod 6.10 5.20 6.54
Intact Mid-plane Quarter
Table 6
16
Flexure properties via 3-point bending method with OFs in the longitudinal direction
0
10
20
30
40
50
60
Number of optical fibres
Fle
xura
l Mo
du
lus
(GP
a)
M 43.6 43.5 43.0 40.6
Sin-Q 43.6 46.8 44.8
Symm-Q 43.8 45.7 39.9
Intact 1 OF 2 OFs 3 OFs 5 OFs0
100
200
300
400
500
600
700
800
900
Number of optical fibres
Fle
xura
l str
eng
th (
MP
a)
M 777 737 719 688
Sin-Q 777 761 764
Symm-Q 777 746 698
Intact 1 OF 2 OFs 3 OFs 5 OFs
Table 7
17
0
10
20
30
40
50
60
Number of optical fibresF
lexu
ral M
od
ulu
s (G
Pa)
M 43.6 37.9 38.5 43.7
Sin-Q 43.6 46.4 40.7 41.1 44.0
Symm-Q 43.8 40.1
Intact 1 OF 2 OFs 3 OFs 5 OFs
Flexure properties via 3-point bending method with OFs in the transverse direction
0
100
200
300
400
500
600
700
800
900
Number of optical fibres
Fle
xura
l str
eng
th (
MP
a)
M 777 697 713 751
Sin-Q 777 701 697 696 717
Symm-Q 777 590
Intact 1 OF 2 OFs 3 OFs 5 OFs
Table 8
-20%
18
3-point bending flexure properties with OFs in the longitudinal direction
0
10
20
30
40
50
60
Position of optical fibres
Fle
xura
l Mo
du
lus
(GP
a)
3th-4th 43.8 44.2
29th-30th 43.8 45.1
3th-4th, 29th-30th 43.8 40.3
Intact 3 OFs0
100
200
300
400
500
600
700
800
900
Position of optical fibres
Fle
xura
l st
ren
gth
(M
Pa)
3th-4th 777 741
29th-30th 777 699
3th-4th, 29th-30th 777 704
Intact 3 OFs
Table 9
19
0
10
20
30
40
50
60
Position of optical fibresF
lexu
ral M
od
ulu
s (G
Pa)
3th-4th 43.8 41.3
29th-30th 43.8 39.6
3th-4th, 29th-30th 43.8 40.4
Intact 5 OFs
3-point bending flexure properties with OFs in the transverse direction
0
100
200
300
400
500
600
700
800
900
Position of optical fibres
Fle
xura
l str
eng
th (
MP
a)
3th-4th 777 698
29th-30th 777 586
3th-4th, 29th-30th 777 532
Intact 5 OFs
Table 10
-25% -32%
20
0
100
200
300
400
500
600
700
800
900
Position of optical fibres
Fle
xura
l str
eng
th (
MP
a)
3th-4th 683 684
29th-30th 683 691
3th-4th, 29th-30th 683 697
Intact 3 OFs0
10
20
30
40
50
60
Position of optical fibres
Fle
xura
l Mo
du
lus
(GP
a)
3th-4th 44.7 45.4
29th-30th 44.7 44.2
3th-4th, 29th-30th 44.7 45.2
Intact 3 OFs
4-point bending flexure properties with 3OFs in the longitudinal direction
Table 11
21
0
10
20
30
40
50
60
Position of optical fibresF
lexu
ral M
od
ulu
s (G
Pa)
3th-4th 44.7 44.9
29th-30th 44.7 45.4
3th-4th, 29th-30th 44.7 43.8
Intact 5 OFs0
100
200
300
400
500
600
700
800
900
Position of optical fibres
Fle
xura
l st
ren
gth
(M
Pa)
3th-4th 683 617
29th-30th 683 585
3th-4th, 29th-30th 683 507
Intact 5 OFs
4-point bending flexure properties with 5 OFs in the transverse direction
Table 12
-14% -26%
22
Micrograph showing 5 embedded OFs
23
0
10
20
30
40
50
60
70
80
Number of SMA wires
Inte
rlam
inar
sh
ear
str
en
gth
(M
Pa)
Q 62.06 66.09 61.03
Intact 3 SMA 5 SMA
SBS ILSS with SMA wires in the longitudinal direction
Table 13
24
0
10
20
30
40
50
60
Number of SMA wires
Fle
xu
ral M
od
ulu
s (
GP
a)
Q 50.3 51.3 49.2
Intact 3 SMA 5 SMA0
200
400
600
800
1000
1200
1400
Number of SMA wires
Fle
xu
re s
tren
gth
(M
Pa)
Q 978.6 994.4 996.9
Intact 3 SMA 5 SMA
3-point bending flexure properties with SMA wires in the longitudinal direction
Table 14
25
Conclusions
• Specimens containing OFsSpecimens containing OFs
– Short-term ILS and flexural moduli:Short-term ILS and flexural moduli: no effect– Short-term flexural strengthShort-term flexural strength with OFs at any TTT
location in the longitudinal direction no effect– Short-term flexural strength degradation:Short-term flexural strength degradation: Transverse / Sym-Q / 3 OFs / 3-point Moderate (20%) Transverse / Single-out Q / 5 OFs / 3-point Significant (25%) Transverse / Sym-out Q / 5 OFs / 3-point Significant (32%) Transverse / Single-out Q / 5 OFs / 4-point Moderate (14%) Transverse / Sym-out Q / 5 OFs / 4-point Significant (26%)
• Specimens containing up to 5 SMA wiresSpecimens containing up to 5 SMA wires
– Short-term ILS strength and modulusShort-term ILS strength and modulus: no effect– Short-term flexural strength and modulusShort-term flexural strength and modulus: no effect