Exploring Mechanical Property Balance in Tufted Carbon ...comptest/proc/files/presentations/Dell'Anno.pdfPorto, 10 April 2006 Exploring Mechanical Property Balance in Tufted Carbon

Porto, 10 April 2006

Exploring Mechanical Property Balance in Tufted Carbon Fabric/EpoxyGiuseppe Dell’Anno1Denis D. Cartié1Giuliano Allegri2Ivana K. Partridge1Amir Rezai3

1 - Composites Centre, Cranfield University, Cranfield, Bedford, MK43 0AL, UK2 - School of Engineering, Cranfield University, Cranfield, Bedford, MK43 0AL, UK3 - BAE Systems, Advanced Technology Centre, Filton, Bristol BS34 7QW, UK


Slide n° 1

Table of ContentsTuftingTufting

Concept and TechnologyConcept and TechnologyMechanical testingMechanical testing

Tensile testTensile testCompression after impact (CAI) testCompression after impact (CAI) test

Bridging lawsBridging lawsSingleSingle--tuft specimen testingtuft specimen testingAnalytical modellingAnalytical modelling

ConclusionsConclusions

Robotic TuftingRobotic Tufting


Slide n° 2

Tufting: the conceptTufting: the concept

Z-pinsPlane of composite

Z-pinning

TuftingStitching

Lock stitches

Modified lock stitches

Chain stitches

Only for p

re-pregs

High thre

ad tensio

n

Two side

access

Needle

Loops

Thread

Laid-up fabric


Slide n° 3

Robotic tufting of dry preformsRobotic tufting of dry preforms

Silastic® 3481Silicone rubber from Dow Corning®

SIL16Silicone foam from Samco®

3mm

3mm


Slide n° 4

Woven 5 harness satin carbon fibre fabric, 0°/90° lay-upRTM grade epoxy resinResin Transfer Moulding: ΔP=2bar, 180°C for 185 minutes


Glass fibre thread Carbon fibre thread

MaterialEC 9 68x3 S260 T8GSaint Gobain® Vetrotex®

CF Sewing yarnToho Tenax®

Specific weight 204g/km 137g/kmFilament type Continuous

Filament count 204 1000Filament Φ 9μm


Slide n° 5

Mesostructure


Tuft diameter in situ =570μmTuft diameter in situ =710μm

Carbon fibre threadGlass fibre thread


Slide n° 6

BS EN ISO 527-4:1997Glass fibre threadLimess® system stereo cameras

Tensile behaviour

Checking with astrain gauge

VicSnap®

Vic3D®

Load/Displacement curve

Cameras Specimen

Fracture path


Slide n° 7

Fracture surfaceCross section of a tufted specimen

Tensile behaviourTensile behaviour

Tensile TestYoung's modulus

54.255.0

50

51

52

53

54

55

56

57

Control GF tufted

GPa

Tensile TestMax stress

476.5 429.8

0

100

200

300

400

500

600

Control GF tufted

MPa

3mm


Slide n° 8

Failure analysisTufts act as crack initiators

Fibre breakage?Resin pockets?Resin impregnation defects?

Tensile behaviourTensile behaviour

VoidsResin pockets

Broken fibres


Slide n° 9

Impact at 15J0°/90° lay-up - 101.6x152.4mm - Specimen fixture according to Boeing BSS 7260

0

500

1000

1500

2000

2500

3000

3500

4000

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02

Time (s)

Forc

e (N

)

Control

Glass fibre tufted

Carbon fibre tufted

Compression after ImpactCompression after Impact


Slide n° 10

Maximum Load

0

500

1000

1500

2000

2500

3000

3500

4000

Control GF tufted CF tufted

Load

(N)

Con

trol

Gla

ss fi

bre

tufte

d

Car

bon

fibre

tufte

d


Impact at 15J0°/90° lay-up - 101.6x152.4mm - Specimen fixture according to Boeing BSS 7260


Slide n° 11

Samples C-scanned before and after impactImages processed with PaintShop® Pro(Apparent) total damaged area unchanged by tufting

Processed ImageAfter ImpactBefore Impact

50mm

50m

mCompression after ImpactCompression after Impact


Slide n° 12

Linear extent of the damage reducedMaximum distance of the damage border from the centre of impact lowered in tufted samples

After Impact


Control

Reduction intufted samples:Glass fibre 11%Carbon fibre 12%


Slide n° 13

Cross section of impacted control specimen


Number of delamination planes reduced by tufting

Delamination sites

ImpactorΦ=20mm

Laminate


Slide n° 14

Cross section of impacted tufted specimen


Number of delamination planes reduced by tufting

Delamination sites

ImpactorΦ=20mm

Laminate


Slide n° 15

Maximum stress @ 0.5mm/min

0

50

100

150

200

250

Control GF tufted CF tufted

Stre

ss a

t fai

lure

(kN

) Increase 27%Increase 25%

Con

trol

Gla

ss fi

bre

tufte

d

Car

bon

fibre

tufte

d


Compression responseSpecimen fixture according to Boeing BSS 7260


Slide n° 16

Aim Determine the mechanical response of a single tuft inserted in a composite laminate Release

film Tuft Laminate

SingleSingle--tuft specimenstuft specimens

Mode I Mode II


Slide n° 17

SEM ofCarbon fibre tuft

after failureunder mode II

40

50

60

70

80

90

100

110

120

0 0.1 0.2 0.3 0.4

Displacement (mm)

Load

(N)

0

50

100

150

200

250

300

0 0.1 0.2 0.3 0.4

Sliding displacement (mm)

Shea

r For

ce (N

)

No evidence of pull-outThe tuft fails on the delamination plane

SingleSingle--tuft specimenstuft specimens

Mode IIMode I

Glass fibre tuft

Carbon fibre tuft

Glass fibre tuft

Carbon fibre tuft

rate 1mm/min rate 0.25mm/min


Slide n° 18

Bridging stiffnesses χI and χII

Analytical model* for through-thickness reinforcement

IP wχ= IIS uχ=

2

22 3

zI

z

k EALEA k L

χ =+ ( )

xII

k LG L

χβ

=

4 xkEI

β = ( ) ( ) ( )2 cos cosh 2 sinh sin sin cosh cos sinh

cos cosh 1L L L L L L L L L

G L LL L

β β β β β β β β ββ β

β β− + − + −

=−

Foundation stiffnesses kz and kxhave to be determined experimentally

ModellingModelling

* G. Allegri, X. Zhang Delamination Bridging Laws for Composite Laminates Reinforced by Through-Thickness Pinssubmitted for publication to Mechanics of Materials


Slide n° 19

ModellingModelling

Mode IIMode I

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.4540

50

60

70

80

90

100

110

120

130

140

Total opening displacement (mm)

Z fo

rce

(N)

ExperimentalModel

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.4540

50

60

70

80

90

100

110

120

Total opening displacement (mm)

Z fo

rce

(N)

ExperimentalModel

0 0.05 0.1 0.15 0.2 0.250

20

40

60

80

100

120

140

160

180

200

220

Total sliding displacement (mm)

X fo

rce

(N)

ExperimentalModel

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50

50

100

150

200

250

300

Total sliding displacement (mm)

X fo

rce

(N)

ExperimentalModel

Glass fibre tuft

Carbon fibre tuft5% agreement

Prediction:

Glass fibre tuft

Carbon fibre tuft10% agreement

Prediction:


Slide n° 20

Conclusions on effects of tufting

Robotic TuftingRobotic Tufting

10% drop in failure load in tension

In-plane Young’s modulus not degraded significantly

Tufts act as crack initiators

CAI increased by ~26%

No tuft pull-out observed under mode I or mode II

Analytical model for the bridging law by single tuft

established


Slide n° 21

Thank youThank youfor your attention!for your attention!

Further information from Further information from [email protected]@cranfield.ac.ukResearch funded by Cranfield University IMRC with industrial conResearch funded by Cranfield University IMRC with industrial contributionstributions

mailto:[email protected]

Table of ContentsMesostructureFailure analysisImpact at 15J�0°/90° lay-up - 101.6x152.4mm - Specimen fixture according to Boeing BSS 7260Impact at 15J�0°/90° lay-up - 101.6x152.4mm - Specimen fixture according to Boeing BSS 7260Compression response�Specimen fixture according to Boeing BSS 7260Conclusions on effects of tufting

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Exploring Mechanical Property Balance in Tufted Carbon ...comptest/proc/files/presentations/Dell'Anno.pdfPorto, 10 April 2006 Exploring Mechanical Property Balance in Tufted Carbon