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Finite Element Simulation of Thermally Bonded

Nonwoven Materials: Development and Analysis

of Discontinuous Model

Xiaonan Hou, Memi Acar and Vadim V. Silberschmidt

Research Group of Mechanics of Advanced MaterialsWolfson School of Mechanical and Manufacturing

Engineering

Loughborough University

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Loughborough University

The Sunday Times (UK) University of the Year 2008-2009

Six Times of Queens Anniversary Prize

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Contents

Nonwoven material

Mechanical properties of thermally bonded nonwoven material

Continuous model

Discontinuous structure of nonwoven material Development of stress calculation method

Orientation distribution function of the nonwoven material

Discontinuous model of thermally bonded nonwoven material

Analysis of discontinuous model

Conclusions

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Nonwoven Material

A nonwoven is a manufactured sheet, web or batt of directionally orrandomly orientated fibres, bonded by friction and/or cohesionand/or adhesion.

Personal care and hygiene: baby diapers,

wipes, etc. Medical: surgical cap, mask, etc.

Human life: vacuum cleaner bags, tents, etc.

Industry: reinforced plastics, industry wipe,

etc.

Building: pipe wrap, concrete mouldinglayers, etc.

Agriculture: greenhouse shading, crop

covers, etc.

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Thermally Bonded Nonwoven

Nonwoven material(polypropylene fibers; density

20 gsm)

Web bonding calendering of thermally

bonded nonwovens (Edana, 2007)

MD

CD

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Mechanical Properties of Low Density Thermally

Bonded Nonwoven Material

High Anisotropy

Discontinuity and

Nonuniformity

Size-dependence

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.25 0.5 0.75 1 1.25 1.5

True Strain (%)

TrueStree(N/mm)

MD

CD

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Continuous Model of Low Density Thermally

Bonded Nonwoven Material

Classic theory of composite material

Basic structure of composite material

(Daniel and Ishai, 2006)

Phase of bonding points

Phase of fibrous network

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Continuous Model of Low Density Thermally

Bonded Nonwoven Material (MD)

Continuous FEA model

Dimensions: 25 mm x 20 mm

(Strain = 150%) (MD)

Von Mises stresses

Effect of Shear (MD)

Mapping of S11

Increase

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Problems of Continuous Models

No reliable experimental results for the

material properties of fibrous network and

bond points

Continuous structure cannot describe

non-uniform density and discontinuous

structure of low density thermally bonded

nonwoven material

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Discontinuous Structure of Nonwoven

Material

Image with X-ray Micro CT

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Nonuniformed Strain Field of Nonwoven

Material (MD)

0% 20% 40% 60%

Strain

60%

0%

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Nonuniformed Strain Field of Nonwoven

Material (CD)

0% 20% 40% 60%

Strain

60%

0%

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Development of Stress Calculation

Method

Sample 1 2 3 4 5 6 Average

Fraction of

effective area (%)

88.01 83.62 78.20 82.61 86.24 71.40 81.68

Converted for threshold 100

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Development of Stress Calculation

Method

is the reaction force

is the stress renormalization factor

is the engineering stress

is the true stress

is the engineering strain

Fabric

Eff

Fabric

Eff

W

W

A

AP

andengEff

Eff K

W

F

)1( EngEngTrue K

F

eng

True

eng

K

PK

1

is the effective area of the fabric

is the overall area of the fabric

is the average effective width of the fabric

is the width of the fabric

EffW

FabricW

EffA

FabricA

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Orientation Distribution Function of

Nonwoven Material

Anisotropic properties

Preferred direction

Nonlinear behaviours

ODF (Orientation Distribution Function)

0

1

2

3

4

5

6

7

8

9

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 0

Bin Range (Degree)

Frequency(%)

Without consideringeffect of curly fibres

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Discontinuous Model of Thermally Bonded

Nonwoven Material

Development of fibrousnetwork (Python programme)

Geometry of fibrous

structure(CD)

Ois the centre point is the angular position

d is the distance from Oto

the line

d

O +

Locations

of bondingpoints =

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Nonwoven Material

Details of meshes

Fibres are represented

using truss elements.

Bonding points are

represented using shellelements.

The nodes connecting

different types of

elements are calculatedbefore meshing the

bonding points.

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Nonwoven Material

Loading DirectionAssembly of the discontinuous model

MD (18950 elements) CD (20181 elements)

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Analysis of Discontinuous Models

Scheme of orientationdistribution

MD

MD

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 0

Degree

Frequency

ofFibre

OD1

OD2

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Analysis of Discontinuous Model

Staggered

MD bond

points

Lined MD

bond

points

Staggered

CDbond

points

Lined CD

bond

points

Schemes of arrangement of bond points

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OD1

OD2

Staggered MDBond Points

Staggered CDBond Points

Lined MDBondPoints

Lined CD BondPoints

OD1/Staggered MD

OD2/Staggered MD

OD1/Staggered CD

OD2/Staggered CD

OD1/Lined MD

OD2/Lined MD

OD1/Lined CD

OD2/Lined CD

OrientationDistribution

Arrangement ofBond Points

Scheme ofGeometry

Models

The models are

being developing

and will be presented

in the coming paper

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OD1/Staggered CDbond

points (strain: 60%)

OD1/Staggered MDbond


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OD2/Staggered CDbond

(strain: 60%)

OD2/ Staggered MDbond


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OD1/Lined CDbond points

(strain: 60%)

OD2/Lined MDbond points

(strain: 40%)

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Analysis of Discontinuous ModelModels with the same fibre's orientation distribution of fibres

0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40 50 60Strain (%)

Stress(N/mm)

OD1/Staggered CD

OD1/Staggered MD

OD1/Lined CD

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 10 20 30 40 50 60Strain (%)

Stress(N/mm

)

OD2/Staggered CD

OD2/Staggered MD

OD2/Lined MD

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Summary & Conclusions

Discontinuous FE models were developed to simulate thediscontinuous structure of the low density thermallybonded nonwoven material, which include physicalinformation of the real material.

A new stress calculation method was suggested to accountfor the effect of voids in the fabric

The results obtained with discontinuous models reveal that

the shape of bond points affects the deformation behaviormore than their arrangement; and the fibers orientationdistribution has a considerable effect on the overallmaterial properties.

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Acknowledgement

NCRC / NC State University

MoAM / Loughborough University

Thank You !

NONWOVENS COOPERATIVE

RESEARCH CENTER

NCSU

IndustryStateofNC

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