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ROUND ROBIN FORMABILITY STUDY Characterisation of glass/polypropylene fabrics Tzvetelina Stoilova Stepan Lomov Leuven, April 2004

Characterisation of woven glass/ polypropylene woven fabrics

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Page 1: Characterisation of woven glass/ polypropylene woven fabrics

ROUND – ROBIN FORMABILITY STUDY

Characterisation of glass/polypropylene fabrics

Tzvetelina Stoilova

Stepan Lomov

Leuven, April 2004

Page 2: Characterisation of woven glass/ polypropylene woven fabrics

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Abstract

Thiereport presents results of measuring geometrical and mechanical properties of three types of glass/polypropilene fabrics (balanced and unbalanced fabrics, plain and twill 2/2 weaves).

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CONTENTS

1 INTRODUCTION.............................................................................................................................. 6

2 SPECIFICATION OF THE FABRICS............................................................................................ 7

3 GEOMETRY OF THE FABRICS.................................................................................................... 9

3.1 MEASUREMENT TECHNIQUE ........................................................................................................... 9 3.2 RESULTS ......................................................................................................................................... 10

4 COMPRESSION TESTS ON THE FABRICS.............................................................................. 12

4.1 MEASUREMENT TECHNIQUE ......................................................................................................... 12 4.2 RESULTS ......................................................................................................................................... 13 4.2.1 FABRIC 1....................................................................................................................................... 13 4.2.2 FABRIC 2....................................................................................................................................... 14 4.2.3 FABRIC 3....................................................................................................................................... 15

5 MECHANICS OF THE YARNS .................................................................................................... 16

5.1 TENSION.......................................................................................................................................... 16 5.2 BENDING ......................................................................................................................................... 18 5.2.1 EXPERIMENTAL TECHNIQUE ......................................................................................................... 18 5.2.2 RESULTS ....................................................................................................................................... 19 5.3 COMPRESSION ................................................................................................................................ 19 5.3.1 EXPERIMENTAL TECHNIQUE ......................................................................................................... 19 5.3.2 RESULTS ....................................................................................................................................... 20

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LIST OF FIGURES Figure 1 Fabric 1 ..................................................................................................................................... 7 Figure 2 Fabic 2....................................................................................................................................... 8 Figure 3 Fabric 3 ..................................................................................................................................... 8 Figure 4 Measurement of the yarn width ................................................................................................ 9 Figure 5 Cross-section of a fabric. Measurements of the dimensions d1 and d2, the spacing p and the

crimp height h .................................................................................................................................. 9 Figure 6 Cross-sections of Fabric 1: warp (above), weft (below) ......................................................... 10 Figure 7 Cross-sections of Fabric 2: warp (above), weft (below) ......................................................... 11 Figure 8 Cross-sections of Fabric 3: warp (above), weft (below) ......................................................... 11 Figure 9 Force-displacement diagram without a sample (Instron), x0 corresponds to the moment of

first contact of the upper and bottom plates (changed from series to series of tests)..................... 12 Figure 10 Compression diagrams, 1st, 2nd and 3rd cycles, fabric 1. Arrow shows the fabric thickness,

measured on the cross-sections ...................................................................................................... 12 Figure 11 Fabric 1. Compression diagrams: Comparison of the compression cycles........................... 13 Figure 12 Fabric 1. Compression diagrams: Nesting effect: almost non-existent................................. 13 Figure 13 Fabric 2. Compression diagrams: Comparison of the compression cycles........................... 14 Figure 14 Fabric 2. Compression diagrams: Nesting effect: approximately 0.1 mm at the highest

compression ................................................................................................................................... 14 Figure 15 Fabric 3. Compression diagrams: Comparison of the compression cycles........................... 15 Figure 16 Fabric 3. Compression diagrams: Nesting effect: approximately 0.05 mm at the highest

compression ................................................................................................................................... 15 Figure 17 Tensile diagram of yarns from the fabric 1(one strand 2400 tex)......................................... 16 Figure 18 Tensile diagram of yarns from fabric 2 (one strand 1870 tex).............................................. 17 Figure 19 Tensile diagram of yarns from fabric 3 (1870 tex). .............................................................. 17 Figure 20 Comparison of the average tensile diagrams of the yarns..................................................... 18 Figure 21 KES-F bending diagrams of the yarns. Settings of the KES-F: SW1=5, SW2=1, X=0.2,

Y=0.5. Yarns from (a) fabric 1; (b) fabric 2, x2; (c) fabric 3......................................................... 19 Figure 22 Compression diagrams, yarns from fabric 1: Raw data. Scale of the thickness axis is 1:5 (0.1

mm on the axis = 0.5 mm in reality) .............................................................................................. 20 Figure 23 Compression diagram, yarns from fabric 1. Points – measurements, thick line – averaged

diagram........................................................................................................................................... 20 Figure 24 Compression diagrams, yarns from fabric 2: Raw data. Scale of the thickness axis is 1:5 (0.1

mm on the axis = 0.5 mm in reality). ............................................................................................. 21 Figure 25 Compression diagram, yarns from fabric 2. Points – measurements, thick line – averaged

diagram........................................................................................................................................... 21 Figure 26 Compression diagrams, yarns from fabric 2: Raw data. Scale of the thickness axis is 1:5 (0.1

mm on the axis = 0.5 mm in reality). ............................................................................................. 22 Figure 27 Compression diagram, yarns from fabric 3. Points – measurements, thick line – averaged

diagram........................................................................................................................................... 22

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Figure 28 Comparison of the compression coefficients of the yarns from the different fabrics. The behaviour is very similar ................................................................................................................ 23

LIST OF TABLES Table 1 Overview of characterisation of the fabrics ............................................................................... 6 Table 2 Parameters of the fabric, specified by the manufacturer ............................................................ 7 Table 3 Geometrical parameters of the fabrics...................................................................................... 10 Table 4 Tensile diagrams of the yarns from fabrics 1-3........................................................................ 16 Table 5 Bending rigidity and bending histeresis of the yarns ............................................................... 19

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1 INTRODUCTION The work reported in this document, is a part of a round-robin deformability study of glass/PP fabrics, initiated at the ESAFORM 2002 conference in Krakow. This report describes measurements of the shear behaviour of woven fabrics produced by Saint–Gobain. The fabrics are woven with commingled yarns, which contain glass/PP in relation 60/40, in twill and plain weave.

The tests were performed by Tzvetelina Stoilova, a Marie-Curie Fellow at the MTM department of the KUleuven (from the Technical University of Sofia in Bulgaria) under supervision of Prof. Stepan Lomov. Specifications of the fabrics were sent from Saint-Gobain Vetrotex (USA) by Ms Marcie Williford. Characterisation of the yarns was done in Centexbel Laboratory in Gent, thereby using the KES-F and INSTRON model 6025 with the help of Mr Van de Welde and Dr Jan Laperre.

Table 1 Overview of characterisation of the fabrics

Specifications Geometrical measurements Mechanical tests Surface Internal (on cross-

sections) 1/2/4-layers Fabrics Areal density

Picks/ends [yarn/cm] Areal density

Spacing Crimp height Thickness

Compression

Yarns Linear density Glass fibre

diameter

Linear density Width

Width Thickness

- Bending - Tension - Compression

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2 SPECIFICATION OF THE FABRICS Table 2 Parameters of the fabric, specified by the manufacturer

Fabric 1 Fabric 2 Fabric 3

Manufacturer’s style TPECU53XXX TPEET44XXX TPEET22XXX*

yarns Glass/PP Glass/PP Glass/PP

Glass fibre diameter, µm 21 18,5 18.5

Weave Twill 2/2 Twill 2/2 Plain

Areal density, g/sq. m 1816 1485 743

Yarns linear density, tex 2x2400 1870 warp

2x1870 weft

1870

Figure 1 Fabric 1

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Figure 2 Fabic 2

Figure 3 Fabric 3

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3 GEOMETRY OF THE FABRICS

3.1 Measurement technique Areal density of the fabrics was measured by weighting the samples ~0.5x0.5 m, linear density of the yarns – by weighting the length of ~1.5 m.

Surface measurements used scanned (1200 dpi) images of the fabrics:

- Picks/ends count was measured at the base of 20 yarns.

- Width of the yarns was measured as the distance between points P1 and P2 (Figure 4), averaged for 20 measurements.

Figure 4 Measurement of the yarn width

Measurements on the cross-sections of the fabrics, both in warp and weft direction, were used to measure:

- dimensions of the yarns

- spacing

- crimp height.

Cross-sections were prepared on samples of the fabrics, impregnated with epoxy resin without any pressure. Measurements were done on scanned (1200 dpi) images of the cross-sections (Figure 5).

Figure 5 Cross-section of a fabric. Measurements of the dimensions d1 and d2, the spacing p and the crimp height h

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3.2 Results Table 3 Geometrical parameters of the fabrics

Fabric 1 Fabric 2 Fabric 3 Warp Linear density, tex (one strand)

2520 2050 2110

d1, mm 1.20 ± 0.29 1.00 ± 0.17 0.90 ± 0.27 d2, mm, in cross-sections 2.29 ± 0.26 1.63 ± 0.26 4.35 ± 0.59

on the surface 2.72±0.38 1.62±0.107 4.18±0.14 End count, yarns/cm 5.26 4.08 1.91 Spacing p, mm, in cross-sections

1.64 ± 0.88 2.56 ± 0.30 4.89 ± 0.46

from the end count 1.90 2.45 5.23 Crimp height h, mm 1.84 ± 0.60 2.28 ± 0.20 0.90 ± 0.30 Weft Linear density, tex (one strand)

2520 2050 2110

d1, mm 0.78 ± 0.08 1.60 ± 0.17 1.17 ± 0.16 d2, mm, in cross-sections 3.92 ± 0.35 4.64 ± 0.26 4.96 ± 0.33

on the surface 3.58±0.21 4.64±0.40 4.22± 0.15 Pick count, yarns/cm 1.52 1.88 1.90 Spacing p, mm, in cross-sections

6.78 ± 0.37 5.27 ± 0.15 5.44 ± 0.35

from the picks count 6.54 5.32 5.23 Crimp height, mm 0.25 ± 0.15 0.20 ± 0.12 1.22 ± 0.33 Fabric Thickness of the fabric 3.8 ±0.2 3.6 ± 0.2 1.9 ± 0.2 Areal density, g/sq m 1900 1550 815

Note: “±” gives standard deviation of 10 measurements

Figure 6 Cross-sections of Fabric 1: warp (above), weft (below)

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Figure 7 Cross-sections of Fabric 2: warp (above), weft (below)

Figure 8 Cross-sections of Fabric 3: warp (above), weft (below)

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4 COMPRESSION TESTS ON THE FABRICS

4.1 Measurement technique Tests were done on the Instron machine, under the speed of 1 mm/min. The sample was placed on a special adjustment table to ensure the alignment of the compressing plates (diameter 35 mm). The stiffness of the machine was accounted for using a force-displacement diagram without the sample (Figure 9).

Three compression cycles were tested for each sample. One, two (and four for the fabric 3) layers of each fabric were tested.

y = 8.4608xR2 = 0.9998

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.02 0.04 0.06 0.08 0.1

x-x0, mm

F, k

N

Figure 9 Force-displacement diagram without a sample (Instron), x0 corresponds to the moment of first contact of the upper and bottom plates (changed from series to series of tests)

The fabrics cannot be laid absolutely flat on the plates of the machine. This leads to the fact that the machine registers compressive force well before the distance between the plates reaches the fabric thickness, shown in Table 3 (Figure 10). If this happens, then in the presentation of the results below, only data below the fabric thickness are retained.

1 layer

22.5

33.5

44.5

55.5

66.5

0 100 200 300 400 500 600 700 800

p, kPa

h, m

m

1st2nd3rd

Figure 10 Compression diagrams, 1st, 2nd and 3rd cycles, fabric 1. Arrow shows the fabric thickness,

measured on the cross-sections

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4.2 Results

4.2.1 Fabric 1

1 layer

2

2.5

3

3.5

4

4.5

0 200 400 600 800

p, kPa

h, m

m

1st

2nd

3rd

2 layers

44.5

55.5

66.5

77.5

88.5

0 500 1000

p, kPah,

mm

1st2nd3rd

Figure 11 Fabric 1. Compression diagrams: Comparison of the compression cycles

2nd cycle

2

2.5

3

3.5

4

4.5

0 200 400 600 800

p, kPa

h, m

m, p

er la

yer

1 layer 2nd

2 layers 2nd

2nd cycle

2

2.1

2.2

2.3

2.4

2.5

0 200 400 600 800

p, kPa

h, m

m, p

er la

yer

1 layer 2nd2 layers 2nd

Figure 12 Fabric 1. Compression diagrams: Nesting effect: almost non-existent

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4.2.2 Fabric 2

1 layer

1.51.71.92.12.32.52.72.93.13.33.5

0 200 400 600 800

p, kPa

h, m

m

1st2nd3rd

2 layers

3

3.5

4

4.5

5

5.5

6

6.5

7

0 200 400 600 800

p, kPah,

mm

1st2nd3rd

Figure 13 Fabric 2. Compression diagrams: Comparison of the compression cycles

2nd cycle

1.5

2

2.5

3

3.5

0 200 400 600 800

p, kPa

h, m

m, p

er la

yer

1 layer 2nd2 layers 2nd

2nd cycle

1.5

1.6

1.7

1.8

1.9

2

0 200 400 600 800

p, kPa

h, m

m, p

er la

yer

1 layer 2nd2 layers 2nd

Figure 14 Fabric 2. Compression diagrams: Nesting effect: approximately 0.1 mm at the highest compression

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4.2.3 Fabric 3

1 layer

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

0 200 400 600 800 1000

p, kPa

h, m

m

1st2nd3rd

2 layers

1.5

1.7

1.9

2.1

2.3

2.5

2.7

2.9

3.1

3.3

3.5

0 200 400 600 800

p, kPa

h, m

m

1st2nd3rd

4 layers

3

3.5

4

4.5

5

5.5

6

0 200 400 600 800

p, kPa

h, m

m

1st2nd3rd

Figure 15 Fabric 3. Compression diagrams: Comparison of the compression cycles

2nd cycle

0.80.9

11.11.21.31.41.51.61.71.8

0 200 400 600 800

p, kPa

h, m

m, p

er la

yer

1 layer 2nd2 layers 2nd4 layers 2nd

2nd cycle

0.8

0.9

1

1.1

1.2

0 200 400 600 800

p, kPa

h, m

m, p

er la

yer

1 layer 2nd2 layers 2nd4 layers 2nd

Figure 16 Fabric 3. Compression diagrams: Nesting effect: approximately 0.05 mm at the highest compression

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5 MECHANICS OF THE YARNS

5.1 Tension Tensile tests were performed in Centexbel lab on the Instron machine at a speed of 10 mm/min and maximum force 200 N. Samples of length 200 mm were used. The diagrams are averages of 3…5 tests on each yarn. The results are shown in Table 4 and Figure 17, Figure 18, Figure 19.

Comparison of the tensile diagrams reveals an interesting result (Figure 20): thicker (2400 tex) yarns from fabric 1 show lower initial resistance then the thinner (1870 tex) yarns from fabrics 2 and 3. This might be explained by the higher misalignment and crimp of the fibres in the former case; however, the scatter of the data is quite large, and the difference between the curves lies inside the scatter.

Table 4 Tensile diagrams of the yarns from fabrics 1-3

Fabric 1, 2400 tex Fabric 2, 1870 tex Fabric 3, 1870 tex ε, % F, N ε, % F, N ε, % F, N

0 0 0 0 0 0 0.5 0.4 0.5 1.4175 0.5 0.6925 1 1.84 1 3.125 1 2.6175

1.5 4.3 1.5 9 1.5 7.6225 2 12.8 2 25.75 2 24.625

2.5 31.92 2.5 71.5 2.5 63.625 3 82.38 3 148.225 3 128.625

3.475 200 3.25 191.725 3.3 196

Fabric 1

0

20

40

60

80

100

120

140

160

180

200

0 1 2 3 4 5 6 7 8

eps, %

F, N

1245ave3 excluded

Figure 17 Tensile diagram of yarns from the fabric 1(one strand 2400 tex).

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Fabric 2

0

20

40

60

80

100

120

140

160

180

200

0 1 2 3

eps, %

F, N

4

1234ave

Figure 18 Tensile diagram of yarns from fabric 2 (one strand 1870 tex).

Fabric 3

0

20

40

60

80

100

120

140

160

180

200

0 1 2 3

eps, %

F, N

4

123456ave

Figure 19 Tensile diagram of yarns from fabric 3 (1870 tex).

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0

50

100

150

200

250

0 1 2 3 4

eps, %

F, N

yarns from fabric 1, 2400 tex

yarns from fabric 2, 1870 tex

yarns from fabric 3, 1870 tex

Figure 20 Comparison of the average tensile diagrams of the yarns

5.2 Bending

5.2.1 Experimental technique

The measurement of the bending resistance is a measurement of dependence of bending moment on curvature of the sample.

The KES-F equipment, which has been used, provides paper plots of the bending curves (see Appendix). The plots are processed using the following formula of the KES-F manual:

21

SWSWYaB ⋅⋅

=

where B is the bending rigidity of the sample, N mm2; a, cm is the difference of the vertical readings of the plot at curvatures 0.5 and 1.5 cm-1 (a characterises the corresponding difference in the bending moment; the plot scale is maintained by the equipment in a way which makes the formula valid); Y, SW1 and SW2 are the settings of switches on the machine and the plotter.

Measurement of heavy rovings presents some difficulties. To cope with them, measurements were performed on the second bending cycle. The behaviour in the first cycle shows large abnormalities, which are explained by the process of “adjustment” of a heavy roving to the deformation. Notably the third cycle is very close to the second. The second cycle data is felt to describe the actual behaviour of the rovings inside a fabric more adequately, as the yarn is subject to bending deformations of changing sign prior to the moment when it acquires the final shape.

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5.2.2 Results

a b

c

Figure 21 KES-F bending diagrams of the yarns. Settings of the KES-F: SW1=5, SW2=1, X=0.2, Y=0.5. Yarns from (a) fabric 1; (b) fabric 2, x2; (c) fabric 3

Table 5 Bending rigidity and bending histeresis of the yarns

Yarns from the fabric Linear density, tex B, N mm2 HB, N mm

1 2400 3.43 ± 0.93 0.35 ± 0.07

2 1870 1.14 ± 0.07 0.14 ± 0.03

3 1870 1.13 ± 0.16 0.071 ± 0.0005

5.3 Compression

5.3.1 Experimental technique

The measurement of the compression resistance is a measurement of dependence of the compression load on the position of the compression head. The maximum load used on KES-F equipment is 100 gf. The compression head is rectangular 4x4 mm. The equipment provides a paper plot of the compression curve.

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Based on the same reasoning as for bending measurements, the second compression cycle was used. The readings of the sample thickness (position of the compression head vis-à-vis the bottom plate) were read from the plot for the load values 2.5, 5, 10, 20, 40, 60, 80 and 100 gf, and the obtained values were averaged for all the samples of a fabric/roving.

As it is evident from the compression curves below, it is impossible to directly read the value of the thickness at zero load. It was computed for each curve by linear extrapolation for the thickness values for the load of 2.5 and 5 gf.

5.3.2 Results

Figure 22 Compression diagrams, yarns from fabric 1: Raw data. Scale of the thickness axis is 1:5 (0.1 mm on the axis = 0.5 mm in reality)

00.20.40.60.8

11.21.41.61.8

0 0.5 1 1.5 2 2.5 3 3.5

P, kPa

d1, m

m

Figure 23 Compression diagram, yarns from fabric 1. Points – measurements, thick line – averaged diagram

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Figure 24 Compression diagrams, yarns from fabric 2: Raw data. Scale of the thickness axis is 1:5 (0.1 mm on the axis = 0.5 mm in reality).

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2 2.5 3 3.5

P, kPa

d1, m

m

Figure 25 Compression diagram, yarns from fabric 2. Points – measurements, thick line – averaged diagram.

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Figure 26 Compression diagrams, yarns from fabric 2: Raw data. Scale of the thickness axis is 1:5 (0.1 mm on the axis = 0.5 mm in reality).

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5 2 2.5 3 3.

P, kPa

d1, m

m

5

Figure 27 Compression diagram, yarns from fabric 3. Points – measurements, thick line – averaged diagram.

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0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2 2.5 3 3.5

p, kPa

eta1

= d

1/d1

0

Fabric 1Fabric 2Fabric 3

Figure 28 Comparison of the compression coefficients of the yarns from the different fabrics. The behaviour is very similar