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