Textile composites: from microstructure to mechanical properties

Stepan V. LomovDepartment of Materials EngineeringKU Leuven, Belgium

08.09.2016

Contents

08.09.2016 S.V. Lomov 1

1. Introduction2. Internal geometry of textile composites: WiseTex software3. Micro-CT reconstruction of the fibrous microstructure4. Conclusion

08.09.2016 S.V. Lomov 2

1. Introduction2. Internal geometry of textile composites: WiseTex software and

around it3. Micro-CT reconstruction of the fibrous microstructure4. Conclusion

Composites in constructions

Windmill blade

Hierarchy of scales: MACRO to meso

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1 km

100 m

10 m

1 m

100 mm

A350 wing

FE model of a composite aeronautic part

Hierarchy of scales: meso to µicro

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100 mm

10 mm

1 mm

100 µm

10 µm

FE: fibre failure

transverse stress in an impregnated yarn

FE model of 3D fabric

Hierarchy of scales: nano to µicro

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Molecular dynamics: interaction CNT -polymer

CNT bending

Carbon nanotubes (CNT) on the surface of a carbon fibre

10 µm

1 µm

100 nm

10 nm

1 nm

Laminates of unidirectional fibre layers

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filament windingBoeing fuselage

Automated fibreplacement (AFP)

Fibrous reinforcements

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Short fibres

• chopped

• non-woven

Long fibres

• tapes (5...500 mm)

• tows (1000 ... 80.000 fibres = 1K … 80K)

• twisted (50...5000 tex)

• commingled (fibres+matrix)

Textile

...

2D textile reinforcements

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Type Structure Fibre orientation in plane

Random fibre mats

Random orientation; fibres can be chopped (short and straight) or continuous (curved)

UD layers Perfectly straight in layers, placed on desired angles

Stitched multi-ply

Almost straight in layers, placed on desired angles; voids formed by stitching

Woven fabrics

Two orthogonal directions (three in triaxial fabrics - rare), slight crimp in z-direction.

Braided fabrics

Two non-orthogonal directions or three if there are inlays, slight crimp in z-direction.

Knitted fabrics

Regular but widely distributed fibre orientation

According to textile manufacturing technology

3D textile reinforcements

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Solid 3D• woven• braided• stitched

Textile sandwiches• woven• knitted

3D shapes• braided• knitted• stitched

Applications and manufacturing

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RTM infusion

autoclave

thermoforming

hand layup

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1. Introduction

2. Internal geometry of textile composites: WiseTex software

3. Micro-CT reconstruction of the fibrous microstructure4. Conclusion

Integrated simulations of textile composites

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x

z

p

h z(x)

Q

Q

d2

d1

Z

A

B

Internal architecture of the reinforcement

Deformation resistance and change of geometry

Compr. Shear Tension Bending

Perme-ability

M

R=1/K

Drapeability and formability

Impregnation

Production

Mechanical properties and damage

Performance

Structural analysis

WiseTex: virtual textile composites

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Internal geometry: textile unit cell

x

z

p

h z(x)

Q

Q

d2

d1

Z

A

B

WiseTex

LamTex

WeftKnit

woven (2D and 3D) braids

weft-knits NCFlaminates

Virtual reality

VRTex

meso-FE

WiseTex -> Ansys

(FETex)

WiseTex -> Abaqus

Composite micromechanics (fast stiffness calculations)

TexComp

Permeability

FlowTex

NX

WiseTex worldwide

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licenses, 2016:

industrial (16)

university (40)

A gallery of WiseTex models

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Data open to the user

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WiseTex or custom software

WiseTex 3.0:

• open XML input and output formats

• “command line” version

New possibilities:

easy integration:

• upstream, with user-defined process models (e.g., braiding process)

• downstream, with user-defined modles of composite (e.g. meso-FE)

XML: textile data

XML: fabricgeometry

custom software

Scripting

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WiseTex 3.0+:

• open XML input and output formats

• “command line” version

New possibilities:

easy integration:

• upstream, with user-defined process models (e.g., braiding process)

• downstream, with user-defined modles of composite (e.g. meso-FE)

scripting:

• parametric studies

• look-up tables (e.g., shear angle)

XML: textile data

XML: fabricgeometry

WiseTex or custom software

custom software

command line script

Multi-level analysis

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WiseTex

Local deformation parameters (thickness, shear…)

Forming

Internal geometry

Local stiffness [Q]

FE analysis

Stress/strain fields

TexComp

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1. Introduction2. Internal geometry of textile composites: WiseTex software

3. Micro-CT reconstruction of the fibrous microstructure

4. ConclusionIlya Straumit

Stepan V. LomovMartine Wevers

Micro computed tomography (micro-CT)

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www.le.ac.uk

Nanotom – GE 0.5 µm

SkyScan, 1 µm

Different textiles

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Modelling workflow

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VoxTex

ABAQUS

FlowTex

Mechanical properties

Voxel (FE) model

Permeability of the composite preform

Stress-strain fields

Structure tensor: Definition

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I – image as three-dimensional function, Ω – image domain, and w(r) – window function.

CT image I

window, defined by w(r)

𝑥1

𝑥3

𝑥2

Structure tensor: Example

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𝑆𝑖𝑗 =16.8 3.6 1.13.6 7.6 0.71.1 0.7 2.8

𝛌 = 𝟐. 𝟕 𝟔. 𝟒 𝟏𝟖. 𝟏

𝑣0 =−0.048−0.1070.993

β = 0.85

Micro-CT image of unidirectional steel fiber reinforced composite.Z is the direction of fibers.

X

Y

Z

Components of the structure tensor:

Eigenvalues:

First eigenvector:

Degree of anisotropy:

Degree of anisotropy

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The ratio of eigenvalues:

𝛽 → 1

𝛽 → 0

anisotropic

isotropic

where 𝜆1 and 𝜆3 are lowest and highest eigenvalues of the structure tensor respectively.

Orientation fields

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Computed orientation fields

isotropic

anisotropic (orientation)

Knitted glass fiber compositeResolution: 4 μm

Segmentation

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grey value – material attenuationstructural anisotropy – material microstructure type

The variables, extracted from the image, reflect physical properties of the material:

Yarns clusterMatrix cluster

Methods of segmentation:• Unsupervised (k-means)• Supervised (Gaussian mixture model)

yarns matrixvoids

Micro-Ct based Abaqus model

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Example: 3D woven composite

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calculated elastic properties

VoxTex software

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Nanotom(3D volume)

VoxTex

ABAQUS

FlowTex

TexComp

Finite element analysis

Permeability

Homogenization (Mori-Tanaka)

ParaView

Visualization

SkyScan,Tomohawk

(image stack)

Root (CERN)

Histograms, statistics

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1. Introduction2. Internal geometry of textile composites: WiseTex software 3. Micro-CT reconstruction of the fibrous microstructure

4. Conclusion

Growing field, steady interest

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0

50

100

150

200

250

300

1980 1990 2000 2010 2020

number of scientific papers on textile composites, per year

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

3.5%

4.0%

4.5%

1980 1990 2000 2010 2020

part of “composite + fibre” papers 235,000

links

Composites in the world

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http://compositesmanufacturingmagazine.com/2015/01/what-will-drive-composites-growth-in-2015/

2013

planned for 2014