Effects of mesostructure on the in plane properties of tufted carbon fabric composites
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Effects of mesostructure on the in-plane properties of tufted carbon fabric composites. CompTest 2011, 14 th February 2011 Johannes W G Treiber Denis D R Cartié Ivana K Partridge [email protected] Tufting process. - Modified one-sided stitching process

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Effects of mesostructure on the in-plane properties of tufted carbon fabric composites

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Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Effects of mesostructure on the in-plane properties of tufted carbon fabric composites

CompTest 2011, 14th February 2011 Johannes W G Treiber

Denis D R Cartié

Ivana K Partridge

[email protected]


Tufting process

Tufting process

- Modified one-sided stitching process

-Automated insertion of carbon, glass or aramid thread

- For dry composite preforms

0.5% carbon tufted NCF

Top

Automated KSL KL150 tufting head

Hollow needle

Presser foot

Dry fabric

Bottom

Tuft thread loop

Support foam

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Introduction

Main purpose: Through-the-thickness reinforcement technique

+ 460%/+60% mode I/II delamination toughness

for only 0.5% areal tuft density (Cranfield)

Tuft bridging

Delamination crack

DCB of 0.5% carbon tufted NCF

Drawback: Potential reduction of in-plane properties

Stitching: - considerable database

Stiffness: -15% to +10%Tensile strength: -25% to +25%

Tufting: - to date only 3 experimental studies (KU Leuven, Cranfield)

Tensile strengths: -14% to +10%

no agreement

Need for detailed testing database on wider range of tufted materials

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

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%)

Square arrangement

  • Cross-over

  • Pattern shift

Free loop height:

3.5 – 5 mm

- RTM injection of epoxy resin (ACG MVR 444) for dimensional control

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

In-plane tension behaviour

Tensile tests (BS EN ISO 527-4:1997):

Property changes depend on fabric and tuft morphology

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Meso-structure

In-plane disturbance (x-y):

Triangular

UD

w ,φ

UD: 6°

NCF: 10°

Resin pocket

Fabric deviation

Tuft

0.5%

2.0%

Square

w

Thermal crack

Square

w,φ

UD: 3°

NCF: 4°

NCF

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Meso-structure

Out-of-plane disturbance (x-z/y-z):

Thread seam

Surface crimp

z

x

Vf = f(wi,tloop, tthread)

Thread layer tth

Loop layer tl

  • Surface seam causes local fabric crimp

  • Resin rich layers and pockets affect global and local Vf

z

y

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Numerical Unit Cell model

φ= cosine fct.

Loop

Vf= f(tl,tth,wi)

¼ UC

Resin channel

Tuft

y

Thread

y

x

wi

‘Smeared’ UD

x

Parametric 3D Unit Cell model (Marc): UD, NCF, square and triangular arrangement

Isotropic, linear elastic material + ‘Rule of mixtures’ (Chamis)

Failure and degradation:

Ply:Puck (FF + 3 modes of IFF)

Resin: Maximum strength

Knops, Comp. Sci. Tech. 2006

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Failure prediction – NCF

0° Ply

¼ UC

A

Transverse tension failure

A

Longitudinal splitting

0.5% NCF||

Cracks

  • 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

Longitudinal splitting

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Failure prediction – NCF

0° Ply

B

¼ UC

B

Fibre failure initiation

0.5% NCF||

Rupture

Tuft

  • Ultimate fabric fibre failure in close vicinity of tuft

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Vf distribution

0.5% NCF||

  • Local fabric fibre distribution affects both stiffness and strength prediction

  • Gradient Vf model agrees best with true morphology and tension results

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Fibre misalignment φ

0.5% square

wmin

  • Fabric fibre deviation critical on tensile strength, effect on modulus negligible

  • UD strength more sensitive to fabric deviation

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Tuft arrangement

UD||

  • Upper and lower strength bounds defined by square and triangular pattern

  • Triangular pattern causes most critical strength reduction

Tufting process

Meso-structure

Exp. database

FE-Models


Effects of mesostructure on the in plane properties of tufted carbon fabric composites

Conclusions

  • 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


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