Mechanical C haracterisationof T hrough-air Bonded N onwoven - - PowerPoint PPT Presentation

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Mechanical C haracterisationof T hrough-air Bonded N

• nwoven

Structures

Amit Rawal*, Stepan Lomov**, Thanh Ngo**, Ignaas Verpoest**and Jozef Vankerrebrouck***

*Current Address: The University of Bolton, Deane Road, Bolton BL3 5AB, UK **Department of Metallurgy and Material Engineering, Katholieke Universiteit, Leuven, Kasteelpark Arenberg, 44, B-3001 Leuven, Belgium ***Libeltex bvba, Marialoopsteenweg 51, 8760 Meulebeke, Belgium

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Contents

• Introduction
• Objectives
• Experimental Work
• Micromechanical Model for Initial Tensile

Behaviour of Through-air Bonded Structures

• Results
• Conclusions
• Potential Outputs

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Introduction

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Definition of Nonwovens*

A fabric consisting of an assembly of textile fibres (oriented in one direction or in a random manner) held together (1) by mechanical interlocking; (2) by fusing of thermoplastic fibres, or (3) by bonding with a rubber, starch, glue, casein, latex, or a cellulose derivative or synthetic resin.

*www.nonwovens.com

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Classification of Nonwovens

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Importance of Mechanical Properties in Nonwoven Structures

Thermal bonded structures undergo various modes of deformation during their end-use

• performance. For example, geotextiles when

placed under the soil exhibit high levels of tensile and compressive modes of

• deformation. Characterisation of tension,

shear, compressional and bending resistance is needed for accurate prediction

• f fabric draping during the formation of a

three-dimensional (3D) shaped composite part for many automotive applications.

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Objectives

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

The main objective of the research work was to characterise the mechanical properties of thermal bonded nonwoven structures namely, tension, bending, shear and compression, including anisotropy in the properties, along with the fibre orientation distribution in the fabric. A simple micromechanical model has also been proposed to investigate the initial tensile behaviour of thermal bonded structures.

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Experimental Work

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Production of Through-air Bonded Structures

C R1 R2 D Web

Properties TB1 TB2 Type of Fibres PET (Bicomponent) PET (Normal) PET (Bicomponent) PET (Normal) Proportion (%) 50 50 50 50 Linear Density (dtex) 2.2 3.3 4.4 12 Computed Diameter (µm) 14.20 17.40 20.15 35.03 Average Length (mm) 48.83 58.38 47.80 61.20

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Fibres Stress-Strain Curve

1 2 3 4 5 6 7 2 4 6 8 10 Strain (%) Stress (cN/tex) 2.2 dtex 3.3 dtex 4.4 dtex 12 dtex

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Properties of Through-air Bonded Nonwovens

0.43 ± 0.0038 28.46 ± 0.031 TB2 0.44 ± 0.0012 31.09 ± 0.082 TB1 Thickness (mm) Mass per unit area (g/m2) Fabric Sample IDs

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Measurement of Mechanical Properties

• Tension: Fabric strips of 20x15 cm were tested
• n an Instron tensile testing machine under

uniaxial loading in a “grab” test. Poisson’s ratio was also determined by measuring the contraction in the centre of the specimen relative to the strain in the test direction.

• Shear: Picture frame was mounted on Instron

tensile testing machine.

• Bending: KES-F B2 (Bending Tester) was used

and the fabric was bent between the curvature of –2.5 and 2.5 cm-1. Three cycles were repeated for each sample in the machine (0° ) and cross- machine (90° ) directions.

• Compression: KES-F B3 (Compression Tester)

was used and the pressure was increased gradually up to 50 g/cm2.

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Measurement of Fibre Orientation Angles

YZ Machine Direction z y XZ x

Sectioning of fabric samples

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Measurement of fibre Orientation Distribution (Cont.)

’

• ’
• b

a

X’ Y’ Z’

px’ py’ pz’

Scheme for computing the fibre orientation angles

2D image analysis software provides the values of minor and major axes along with an in-plane fibre orientation angle ´

) / arccos( a b

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Ambiguities, Errors and Corrections in 2D Image Analysis

• Ambiguity: There are two possible values

for fibre in the in-plane orientation angle ( ) as the fibres with orientations and + 180 have identical cross-sections.

• Correction: Assuming the orientation

distribution to be symmetrical, and the out-

• f-plane orientation angle is randomised

by using the following equation.

• ´1 = (sign (RAND (0,1)-0.5) ’
• 1

1 1 x x x x sign , , , ) (

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Ambiguities, Errors and Corrections in 2D Image Analysis (Cont.)

• Ambiguity: The probability of finding a fibre with

defined orientation ( ) such that it has an elliptical cross-section on the sectioning plane.

• Correction: The “probability of intersection”

between the fibre and the sectioning plane has been determined by dividing the fibre orientation distribution with cosine of the sectioning angle (Zak et al., 2001).

• ,

’

( , ) cos

XZ

i j XZ ijcorrected i

• Zak, G., Park, C. B. and Benhabib, B., Estimation of three-dimensional fibre-orientation

distribution in short-fibre composites by a two-section method, Journal of Composite Materials, 35, 316-339 (2001).

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Ambiguities, Errors and Corrections in 2D Image Analysis (Cont.)

• Error: Small errors in the measurement of

elliptical axes for the fibres oriented nearly perpendicular ( ) to the sectioning plane can yield large errors in the measured value of (Mlekusch, 1999).

• Correction: Fitting a normal distribution to the

measured values of in-plane fibre orientation angles .

• Mlekusch, B., Fibre-orientation in short-glass-fibre composites II: Quantitative measurements by

image analysis, Composites Science and Technology, 59, 547-560 (1999).

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Micro-mechanical Model for Initial Tensile behaviour of Through-air Bonded Nonwoven Structures

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

A simple micro-mechanical model has been developed to predict the anisotropy of the tensile properties of through-air bonded structures. The model is based on the averaging schemes of bond distribution and fibre orientation proposed by Pan et al.(1993), Komori and Makashima (1977, 1978) and Lee and Lee (1985).

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Assumptions

• Each fibre segment is straight before

loading, i.e. local fibre crimp is neglected.

• The constituent fibres of same type

have identical properties and are elastic.

• Bending, torsion and compression

deformations of the fibre segments and compliance of bond are neglected.

• Fibres do not slip past each other.

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Calculation of Number of Contacts

Assuming the centre of fibre B ( ) is brought into contact with the surface of fibre A ( ), then the parallelepiped consisting

• f two rhombuses of length l and

height 2D, where D is the diameter of the fibre.

• ,
• ,
• sin

2 ) , , , (

2

Dl v

• where V is the total volume

P is the probability that fibre A will contact with fibre B is the angle between the two neighbouring axes of fibres A and B

V Dl P

• sin

2

2

• Contact of Fibre A with Fibre B

(Komori and Makashima, 1977)

) cos( sin sin cos cos cos

• 1. Komori, T., and Makishima, K., Numbers of fibre-to-fibre Contacts in General fibre Assemblies, Textile Research Journal, 47, (1977).

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Calculation of Real Number

• f Contacts

Total number of contact places in whole fibrous assembly (m)

Real contact between the fibres

V I l DN V I l N DN m

2 2 2

2 ) 1 ( 2

• )

, ( sin ) , ( d J d I

• sin

) , ( ) , , , ( sin ) , ( d d J

V I DL V I l DN m n

2 2 2

2

• where N is the total number of fibres

L is the total length in the volume V n is the real number of contacts between the fibres (as N>>1) 1 contact = 2 contact places

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Formulation of Micromechanical Model

Consider a tension test in the direction with respect to the machine direction. Here, volume ( ) of the sample, having a unit cross-sectional area (A=1) that is limited by two planes normal to the test direction.

According to Lee and Lee (1985), Projections of a fibre length between two bonds

is the directional parameter indicating the length projections

• f the fibres on the test direction.

is the projection of the average length of the fibre between two bonds ( ) on the test direction

• K
• b
• b

b

1

A

• dV
• K

DLI V K b b 2

• b
• ✄

sin b

) sin( sin b

) cos( sin b

/2 2 / 2

sin cos( ) ( , ) K d d

• ✍

• Assuming the fibres lying parallel to X-Y plane,

therefore,

/2 /2

cos( ) ( ) K d

• ✓

• b

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Formulation of Micromechanical Model (Cont.)

Number of bonding points ( ) inside the volume dV:

Projection of the fibre on the test direction

where D is the fibre diameter Vf is the Volume Fraction n is the real number of contacts formed in volume V be a frequency of i-th bin of a histogram, representing this distribution as a function of the angle ( ) between the test and the fibre directions

dV

n

dV

b A n n V

• 2

DL n I V

• 2

2

f dV

V n K D

• 1

2 cos ( )

n f i i dV i i

F n

• f

F

• f

F

• f

F

Bond

• i

• i

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Formulation of Micromechanical Model (Cont.)

where subscripts 1 and 2 refer to the components of the blend, 1 and 2 are fractions of the components (1+2=1) is fabric web stress per unit width m is mass per unit area of the fabric is fibre stress is Poisson’s ratio

• n

i i i i f i i

mK T

1

); , ( ) ( cos ) (

• 1

sin ) 1 ( ) 1 ( cos ) (

2 / 1 2 2 2 2

• f

f

f f

• ’

f

l

f

l

• sin

f

l

• cos

f

l

• cos

f

l

O A B C B’ A’ A c

• n

i i i n i i f i i i f i i

mK mK T

1 1 2 2 2 1 1 1

; ) , ( ) ( cos ) , ( ) ( cos ) ( Relationship between web and fibre strain

) ( T

f

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Results

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Tensile Properties of Through-air Bonded Structures

• The slope of curves decreases with the angle of test, showing high degree
• f anisotropy of the tensile resistance.
• The ratio of tensile strength in the machine direction to the cross-machine

direction of thermal bonded structures TB1 and TB2 was found to be 3.3 and 3.5, respectively.

• TB1 has lower tensile strength in comparison to TB2 in all the test

directions, although the fibres (4.4 and 12 dtex) used in the production of TB2 have high tensile strength in comparison to the fibres (2.2 and 3.3 dtex) used in TB1.

0.1 0.2 0.3 0.4 0.5 0.6 20 40 60 80

Strain (%) Stress (N/mm)

0° 22.5° 45° 67.5° 90°

0.1 0.2 0.3 0.4 0.5 0.6 20 40 60 80 Strain (%) Stress (N/mm)

0° 22.5° 45° 67.5° 90°

TB1 TB2

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Tensile Properties of Through-air Bonded Structures (Cont.)

• Ratio of 20-50 between the secant moduli in 0°and

90°directions.

• Slope of curves steeply decreases between 0 and

22.5° .

Secant moduli of thermal bonded structures TB1 and TB2 at 3.5 % strain

5 10 15 20 25 22.5 45 67.5 90 Test Angle (o)

Secant modulus (MPa)

TB1 TB2

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Shear Properties of Through-air Bonded Nonwoven Structures

• The first shear cycle describes as the sample installation on the frame

rather than the actual material behaviour.

• Initial high shear stiffness (up to shear angles of 3°

) represents bond resistance that is sufficient to prevent rotation of the fibres in the thermal bonded nonwoven structure. Later, bond resistance is

• vercome and the shear resistance is primarily dominated by the

rotation of structural elements of the fabric.

• TB1 requires more shear force than nonwoven TB2 at higher shear

angles although both fabrics have similar weight and thickness.

• The scatter of the local shear angle is high, i.e. 16°to 32°at a frame

shear angle of 30° .

0.005 0.01 0.015 0.02 0.025 10 20 30 40 50

Shear Angle (o) Shear Force per unit width (N/mm)

1st 2nd 3rd

0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 10 20 30 40 50 Shear Angle (O) Shear Force (N/mm)

TB1 TB2

Typical diagrams for the three shear cycles (TB1) Comparison of shear diagrams of TB1 and TB2

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Compressional Properties of Through- air Bonded Nonwoven Structures

• Lee and Lee (1985) have reported that compressional forces are

generally transmitted through the contact points.

• Three cycles produced similar results in all the three positions.
• At lower pressure (up to 5 g/cm2), both through-air bonded structures

follow the same curve. However at higher pressure, the thermal bonded structure TB2 is slightly more compressible than TB1.

5 10 15 20 25 30 35 40 45 50 0.2 0.4 0.6 0.8 1 1.2 1.4 Thickness (mm) Pressure (gf/cm2) TB1 TB2

Relationship between the pressure and thickness of thermal bonded nonwovens TB1 and TB2

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Bending Properties of Through-air Bonded Nonwoven Structures

• 0.2
• 0.1

0.1 0.2

• 3
• 2
• 1

1 2 3 Radius of Curvature (cm -1) Bending Moment (gf.cm/cm) TB1 TB2 a

• 0.08
• 0.04

0.04 0.08

• 3
• 2
• 1

1 2 3

Radius of Curvature (cm -1) Bending Moment (gf.cm/cm)

TB1 TB2 b

0.74 2.94 1.27 3.23 Bending hysteresis, 2HB, 10-4 Nm/m 0.19 0.52 0.26 0.45 Bending rigidity, B, 10-5 Nm2/m Cross-Machine Direction Machine Direction Cross-Machine Direction Machine Direction TB2 TB1 Parameters

Bending diagrams of fabrics TB1 and TB2 in (a) machine and (b) cross-machine directions Parameters of the bending resistance of Through-air bonded nonwoven structures

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Bending Properties of Through-air Bonded Nonwoven Structures (Cont.)

• The fabrics are significantly (2-3 times) stiffer in bending

in the machine (0° ) direction than in the cross-machine direction, which is easily explained by the preferential

• rientation of the fibres in the machine direction.
• The bending hysteresis values are quite small, indicating

reversibility of the bending deformation and hence strong and elastic bonds between the fibres.

• The bending diagrams are linear for the cross-machine

direction and non-linear for the machine direction. This correlates well with the higher hysteresis values for the machine direction and indicates the presence of the frictional component of the bending resistance.

• The bending resistance of fabric TB1 is higher than TB2

in the cross-machine direction. The same arguments of higher density of the finer fibres and lower local porosities in the nonwoven TB1 can explain the observed difference.

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Comparison of Theoretical and Experimental Results of Initial Tensile Response

a

0.1 0.2 0.3 0.4 0.5 1 2 3 4 5 6 7 8 Strain (% ) Stress (N/mm)

Experimental

• Incl. Poisson’s Ratio
• Excl. Poisson’s Ratio

b

0.2 0.4 0.6 0.8 1 2 3 4 5 6 7 8 Strain (%) Stress (N/mm)

Experimental

• Incl. Poisson’s Ratio
• Excl. Poisson’s Ratio

Comparison between experimental and theoretical stress–strain curves of thermal bonded structures (a) TB1, 0° ; (b) TB2, 0° ; (c) TB1, 67.5° ; (d) TB2, 67.5° .

c

0.02 0.04 0.06 0.08 1 2 3 4 5 6 7 8 Strain (%) Stress (N/mm)

Experimental

• Incl. Poisson’s Ratio
• Excl. Poisson’s Ratio

d

0.02 0.04 0.06 1 2 3 4 5 6 7 8 Strain (% ) Stress (N/mm)

Experimental

• Incl. Poisson’s Ratio
• Excl. Poisson’s Ratio

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Comparison of Theoretical and Experimental Results of Initial Tensile Response

Comparison between theoretical and experimental secant modulus of through-air structures (a) TB1 (b) TB2 at 4.17 % strain in various test directions

a

5 10 15 20 22.5 45 67.5 90 Test Angle (o) Secant Modulus (MPa)

Experimental

• Incl. Poisson’s Ratio
• Excl. Poisson’s Ratio

b

5 10 15 20 22.5 45 67.5 90 Test Angle (o) Secant Modulus (MPa)

Experimental

• Incl. Poisson’s Ratio
• Excl. Poisson’s Ratio

There is a distinct difference between the theoretical and experimental values of secant modulus in test directions, 0 and 45°(TB1) and 22.5°(TB2). The deviations from the experimental observations may have been caused by the assumption that the distribution of in-plane orientation of the fibres to be normal. This may have exaggerated the number of fibres oriented in these directions.

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Theoretical Stress-Strain Curves

Theoretical stress-strain curves of through-air bonded structure TB2 (a) including and (b) excluding the effect of Poisson’s ratio

a 0.1 0.2 0.3 0.4 0.5 1 2 3 4 5 6 7 8 Strain (% ) Stress (N/mm)

0° 22.5° 45° 67.5° 90°

b

0.2 0.4 0.6 0.8 1 2 3 4 5 6 7 8 Strain (% ) Stress (N/mm)

0° 22.5° 45° 67.5° 90°

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Conclusions

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

• The mechanical properties namely, tension,

compression, bending and shear of two through-air bonded nonwovens of similar weight and thickness have been investigated.

• The anisotropic characteristics of the properties in

relation to the fibre orientation distributions have been studied.

• The observed behaviour correlates well with the

directional anisotropy and with the peculiarities of the structural characteristics (different fineness of the fibres and observed porosity).

• The initial tensile response of through-air bonded

nonwoven structures has been modelled based upon

• rientation averaging and simple fibre deformation

scheme, taking into account the effect of Poisson’s ratio.

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Potential Outputs

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

• Measurements of orientation distribution of fibres using the

2D image analysis of the fabric cross-sections are subjected to errors for fibres oriented normal to the section plane. These errors should be corrected using general hypothesis

• f the type of the distribution function.
• Anisotropy of tensile and bending behaviour of the through-

air bonded nonwoven fabrics correlates well with the anisotropy of orientation distribution of the fibres. The tensile resistance can be reasonably estimated using simple

• rientation averaging approach.
• In all the mechanical tests (tension, bending and shear) the

frictional losses are small, suggesting good stability and elasticity of the thermal bonds.

• The picture frame technique can be used to study the shear

behaviour of nonwoven structures in the wide range of the shear angles. The second and third shear loading cycles should be used for the characterisation of the shear behaviour.

• Optical full field measurement of the strain is a promising

instrument to study the unevenness of nonwoven structures.

downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm

Acknowledgements

• IWT, Flanders.
• Libeltex and Centexbel, Belgium.
• DWI, RWTH Aachen for performing the

KES-F tests.