Experimental determination of fabric shear by yarn pull-out method

Abstract

The aim of this study was to determine fabric shear by the yarn pull-out method. For this purpose three fabric types were tested. The fabric width/length ratio and the number of pull-out ends were identified as important test parameters. After the yarn in the fabric was pulled from the top ravel region before the start of the crimp extension stage, it was found that fabric shear strength increased as the number of pulled ends increased. On the other hand, when the fabric width/length ratio decreased the fabric shear strength increased. Fabric shear rigidity was also identified for each fabric type and it was found that the number of pulled ends and the fabric width/length ratio influenced fabric shear rigidity. Finally, shear jamming angles were found to be a function of the number of pulled ends. Local fabric shear properties could be identified by pulling the yarn ends in various regions of the fabric. This could be important for the handling of a fabric during its formation. The pull-out method is considered to be a simple way of defining overall and local fabric shear properties for various end-uses.

Keywords

Fabric shear single and multiple yarn pull-outs yarn crimp extension shear rigidity fabric sample sizes pull-out fixture

Introduction

Shearing allows dry fabric to be formed into complex shapes.¹ A simple shear device attached to a tensile tester was developed to measure the shear applied to a fabric, and the shear force angular deformation before the development of local wrinkles and internal yarn-to-yarn friction in the fabric structure were identified. It was observed that the largest shear angular deviation was obtained at the time wrinkles appeared.² Behre found that cross-head rate had little effect on fabric shear and that preload can be applied to the fabric sample; the influence of fabric sample width was limited.³ The energy loss of the total work carried out indicated large frictional losses at high normal stresses at yarn cross-over points. In addition, Spivak found that rectangular specimens were better than square specimens due to the tendency of the latter to wrinkle during shearing.⁴ On the other hand, it was observed that hysteresis occurred when the direction of shear was reversed, due to the shear overcoming the frictional forces in the intersection between warp and weft. Frictional forces are always opposed to the applied shear force.⁵ A shear tester (KES–F) was developed, based on a simple shear test principle, to measure the shear properties of fabric under constant tension.⁶ A flexible automated robotic shear test was also developed in which the fabric sample was mounted between a fixed clamp and one attached to the robot arm, allowing the shear test to be conducted under constant tension.⁷

Another method for measuring fabric shear is by bias extension, in which a rectangular fabric sample is cut at 45° to the principal yarn direction and a uniaxial tensile load applied to identify the shear angle.⁸^–¹¹ In addition, a fixture was added to the bias-extension method, called a picture-frame (or trellis-frame), allowing the shear test to be conducted on a square fabric sample when the shear lock limit was reached.¹²^–¹³ A modified picture-frame fixture in which yarns at the fabric edges were removed to avoid contact between the fixture and the fabric sample, was used to investigate in-plane shear properties.¹⁴ When the E-glass fabric sample was sheared until the locking angle was reached, when a large in-plane shear angle was obtained, it was found that the reduction in yarn width in the fabric was a key indicator for wrinkling, which is crucially important in composite molding.¹⁴ The shear behavior of fabric and the phenomenon of buckling were analyzed during bias-extension shear, in which the image analysis method was proposed for defining critical shear conditions.¹⁵ Recently, fabric shear at bias-extension has been measured by a tensile instrument equipped with a capstan in order to apply tension to the sample gradually.¹⁶ In this way, stress concentration around the jaw area of the fabric was avoided. Another study has shown that there may be inconsistencies between fabric properties measured during simple shear and by bias extension due to factors including specimen geometry, thread properties and variation in normal stress during bias-extension.^1,9

It has been suggested that a new concept of tester was required, in which tensile and shear forces could be applied simultaneously.¹⁷ The shear deformation of a fabric under biaxial load was therefore analyzed by a cylinder shear device in which the fabric remained under constant air pressure.¹⁸ A biaxial tension/shear fixture (using a rotary-frame or cruciform sample) was developed. Biaxial tensile forces resulting from pressurization caused in-plane deformations which were dominated by inter-fiber slippage and crimp interchange. When a fabric was then subjected to in-plane shear stress, the fibers sheared and were rotated in relation to their initial position. The initial resistance to shear-induced rotation in a fabric was the contact-based friction developed at the cross-over points. As the shear rotation increased, the shear locking limit was reached when the warp and the weft yarns became close to each other. Further shear loading induced localized wrinkling, leading to out-of-plane deformation.¹⁹

Fabric shear behavior was found to depend on the applied tension, specimen size and fabric sett. Buckling in the specimen affects fabric shear rigidity.²⁰^–²² It was observed that the limits of shear were usually determined geometrically. For a wide range of conventional fabrics the shear limit is defined by the side-by-side contact of one set of yarns.²³ On the other hand, it has been found that 2D- and 3D-woven preform fabric structures formed into various shapes were highly dependent on the fabric architecture, which influenced the resultant mechanical properties of the composite element during formation, and that the picture-frame test was capable of characterizing the shear deformation of a dry carbon fabric.²⁴ The mechanism of shear, and the yarn slippage of fabrics in which yarn of high bending rigidity showed significant slippage in the fabric during the picture-frame test, were also analyzed.²⁵ Using the picture-frame shear test microstructural analysis was carried out in E-glass fabrics to investigate shear locking, on the basis of a geometrical approach and the maximum packing fiber fraction,²⁶ and it was shown that the initial tension affected the in-plane shearing properties of the fabric.²⁷ In addition, shear angle was predicted up to the shear lock limit with pin-joint assumption to find a relationship between shear angle and wrinkling of the multilayer woven fabric structure.²⁸ It was reported that the unit cell architectures of 3D dry angle interlock preforms were an important parameter of shearing properties.²⁹

An edge-clamped fabric holding fixture was developed. However, transverse tension applied to the fabric through a spring-mounted sliding-edge clamp prevented measurement of the simple shear of the fabric.^30,31 A similar fixture was used to conduct a fabric pull-out test in which small fabric dimensions were chosen (51 mm length × 7 mm width) to prevent shear deformation and transverse tension induced by the pull-out force.³²

The aim of the present study was to determine fabric shear by the pull-out method and to interpret the shear behavior of various dry fabrics based on the data generated.

Experimental principles

Shear force/angle relationship

Schematic views of the samples before and after fabric shear in the pull-out test are shown in Figure 1. We can use simple shear relations to calculate the shear angle:

(1)

and using simple shear relationships, we obtain

(2)

Figure 1.

Schematic views of the fabric and yarn pulled ends for fabric shear by pull-out test: (left) initial fabric position before fabric shear by pull-out test, and (right) fabric shear before crimp extension starts.

Shear angle may be defined (in degrees) as

(3)

where w is fabric width, θ is shear angle, and d is shear displacement.

In addition, shear rigidity from the simple shear can be considered as¹

(4)

Shear rigidity can then be expressed as

(5)

Specific shear rigidity can be defined as

(6)

where F is the pull-out force, w the fabric width, F/w is the shear stress, tan θ the shear strain, G the shear rigidity, W_f the fabric areal weight, and G_sf the specific shear rigidity.

Materials and methods

Woven fabrics

Three types of fabric were considered: polyester, para-aramid and E-glass. Continuous filaments of polyester air-entangled textured yarn were used to produce woven fabrics. The linear density of this yarn was 33.33 tex and it contained 68 filaments in cross-section. It also had 10/10 cm entanglement. The woven fabric was designed as 1/1 plain. A similar fabric was constructed from para-aramid fibers (Twaron®, Teijin, Japan). This comprised Twaron CT 714; it was in plain weave, and the density of the warp and fillings was 8.5 ends/cm. E-glass woven fabric (Cam Elyaf AS, Turkey) was used in plain weave using 2400 tex fibers and the density of the warp and fillings were 1.6 and 1.8 ends/cm, respectively. The fabric properties are presented in Table 1.³³^–³⁵

Table 1.

Specifications of woven fabrics.³³^–³⁵

Fabric type	Weave type	Yarn linear density (tex)		Density (ends/cm)		Crimp (%)		Fabric areal weight (W_f, g/m²)	Thickness (mm)	Treatment
Fabric type	Weave type	weft	warp	weft	warp	weft	warp	Fabric areal weight (W_f, g/m²)	Thickness (mm)	Treatment
Polyester	Plain	33.33	33.33	18	38	4.62	20.08	219	0.57	No treatment
Para-aramid (Twaron CT 714)	Plain	110	110	8.5	8.5	1.98	1.38	190	0.30	Water repellent
E-glass	Plain	2400	2400	1.8	1.6	1.20	1.24	800	1.01	No treatment

Crimp was measured using a Tautex digital instrument (James H. Heal, UK) according to ISO 7211–3. The fabric thickness was measured using an Elastocon EV07 digital device. The fabric weight was measured based on ISO 6348 by using an Ohaus Adventurer Pro AV812 digital balance (Ohaus, USA).

Pull-out tests for shear

A pull-out fixture was developed to determine fabric shear in the frayed edge of the plain fabric structure without pre-tension. The fixture consisted of a base to hold the test instrument a sliding frame to adjust the position of the yarn end to be pulled from the test instrument, and a fabric holder with nine screws to apply the required pressure to both edges of the fabric sample via a metal plate.³⁴ Figure 2 shows the fixture with fabric present, and the pull-out test carried out in the testing instrument (Instron 4411). The test speed was 100 mm/min.

Figure 2.

Pull-out fixture (left) for fabric sample pull-out fixture, and (right) fabric on the tensile testing instrument.

The fabric dimensions used to determine fabric shear by the pull-out test are presented in Table 2. Figure 3 shows the actual and schematic views of the fabric shear samples. The fabric width was 35 cm for the total sample, and 30 cm for the sample in the fixture. The pull-out direction was in either the warp or weft direction of the fabrics. The frayed yarn length in the sample was 15 cm and the total edge length holding the sample in the fixture edge was 5 cm. The fabric sample width/length ratio of 10/1 has been proposed by Spivak⁴ as the limit for practical measurement, and for this reason the width/length ratios of the fabric samples used in the present study are also given in Table 2. The Instron 4411 pull head was able to draw the individual yarn ends from the frayed edge of a single fabric.

Figure 3.

Sample of woven fabrics for fabric shear in various fabric lengths.

Table 2.

Pull-out test dimensions of woven fabric samples

Fabric type	Fabric direction	Sample dimension in the fixture width × length (cm × cm)	Total sample dimension width × length (cm × cm)	Width/length ratio
Polyester	Weft	30 × 10	36 × 25	3/1
		30 × 20	36 × 35	1.5/1
		30 × 30	36 × 45	1/1
Para-aramid (Twaron CT 714)	Warp	30 × 5	36 × 20	6/1
		30 × 10	36 × 25	3/1
		30 × 20	36 × 35	1.5/1
		30 × 35	36 × 50	0.86/1
E-glass	Warp	30 × 10	35 × 20	3/1
E-glass	Warp	30 × 20	35 × 30	1.5/1

In the fabric shear test, shear displacement (described by Bilisik K and Korkmaz M as fabric displacement^33,34) and shear force were measured. Shear displacement can be defined as the displacement due to the tensile load applied on single or multiple yarn ends in the fabric just before crimp extension starts. Crimp extension is defined as the yarn length produced by the applied tensile load on a single yarn end in the fabric structure due to interlacement.³³ In addition, the shear angle was calculated based on shear displacement. Shear rigidity was calculated based on simple shear principles.

Shear jamming

The minimum jamming condition is defined as the minimum shear angle resulting after the fabric is sheared under the minimum number of yarn ends, and the maximum jamming condition is the maximum shear angle after the fabric is sheared under the maximum number of yarn ends.

Results and discussion

Shear force angle results

Fabric shear was carried out using the yarn pull-out test on low modulus polyester fabric, high moduli para-aramid and E-glass fabric samples.

Figure 4 shows the shear force angle curves for shearing the fillings in the fabric as the tensile pulling force is applied to the warp yarns. Based on these results, the shear force angle curve may be defined and is shown in Figure 4.

Figure 4.

Woven fabric shear force angle curve in warp direction of fabric A and B before crimp extension stage. (fabric: para-aramid Twaron CT 714, pulled ends: 5 yarns, fabric width and length: 30 × 20 cm).

When the pulled yarn reaches the point just before the crimp extension stage starts, this is defined as the maximum shear force displacement. As is seen in Figure 4, there are two regions in the fabric, indicated A and B, with maximum shear force displacement. The yarn pulled region is at the center of the fabric. The A and B regions in the fabric are considered to be equal. In this case, the shear force displacement curves in regions A and B are equal to one other but are in opposite regions in the coordinate system.

The tensile base pulled forces and equivalent fabric displacements were recorded. The fabric displacement was then converted to angular displacement using Equation (3). The shear force angle curves obtained from the yarn pull-out test appeared to be similar to those in the simple shear and bias extension shear methods. The initial position of the curves was in proportion, but the curves then showed a non-linear behavior in which there was virtually no shear angle rotation resulting from the increasing degree of shear force.

The test results are presented in Tables 3, 4 and 5.

Table 3.

Shear results of polyester fabrics on pull-out test

Fabric type	Fabric direction	Fabric width (cm)	Fabric length (cm)	Ends of yarn	Shear displacement		Shear force (N)	Shear rigidity (N/m°)	Specific shear rigidity
Fabric type	Fabric direction	Fabric width (cm)	Fabric length (cm)	Ends of yarn	(mm)	(°)	Shear force (N)	Shear rigidity (N/m°)	(N/m° g.m⁻²)
Polyester	Weft	30	10	1 yarn	7	2.66	2.68	192.52	0.88
				2 yarns	17	6.49	5.90	173.00	0.79
				3 yarns	22	8.38	10.46	236.75	1.08
				4 yarns	23	8.75	8.85	191.75	0.88
				5 yarns	30	11.28	15.04	251.31	1.15
	Weft	30	20	1 yarn	6	2.31	2.01	166.01	0.76
				2 yarns	17	6.49	5.50	161.08	0.74
				3 yarns	22	8.37	9.53	215.96	0.99
				4 yarns	32	12.07	16.11	251.02	1.15
				5 yarns	35	13.15	22.15	313.61	1.43
	Weft	30	30	1 yarn	3	1.18	1.74	281.36	1.28
				2 yarns	16	6.07	6.57	206.09	0.94
				3 yarns	22	8.35	12.62	286.50	1.31
				4 yarns	28	10.61	17.72	315.41	1.44
				5 yarns	32	12.08	25.51	397.36	1.81

Table 4.

Shear results of para-aramid fabrics on pull-out test

Fabric type	Fabric direction	Fabric width (cm)	Fabric length (cm)	Ends of yarn	Shear displacement		Shear force (N)	Shear rigidity (N/m °)	Specific shear rigidity
Fabric type	Fabric direction	Fabric width (cm)	Fabric length (cm)	Ends of yarn	(mm)	(°)	Shear force (N)	Shear rigidity (N/m °)	(N/m° g.m⁻²)
Para-aramid (Twaron CT 714)	Warp	30	5	1 yarn	5	1.94	2.02	199.05	1.05
				2 yarns	6	2.31	5.36	443.41	2.33
				3 yarns	8	3.08	7.11	439.98	2.32
				4 yarns	9	3.47	11.00	605.32	3.19
				5 yarns	10	3.80	12.75	639.70	3.37
				6 yarns	12	4.68	17.32	705.49	3.71
				7 yarns	10	3.81	21.62	1083.37	5.70
				8 yarns	16	6.19	20.01	614.76	3.24
				9 yarns	17	6.64	36.11	1034.63	5.45
	Warp	30	10	1 yarn	4	1.55	2.28	281.14	1.48
				2 yarns	15	5.75	7.24	239.78	1.26
				3 yarns	15	5.73	18.26	606.17	3.19
				4 yarns	18	6.86	23.23	643.24	3.39
				5 yarns	20	7.64	43.24	1073.62	5.65
				6 yarns	20	7.63	55.72	1386.86	7.30
	Warp	30	20	1 yarn	7	2.71	7.11	500.22	2.63
				2 yarns	16	6.11	7.91	246.52	1.30
				3 yarns	18	6.86	15.84	438.69	2.31
				4 yarns	20	7.61	28.46	710.25	3.74
				5 yarns	20	7.63	19.33	481.04	2.53
				6 yarns	22	8.32	51.56	1174.72	6.18
				7 yarns	22	8.33	123.12	2803.14	14.75
				8 yarns	26	9.93	420.82	8008.08	42.15
	Warp	30	35	1 yarn	8	3.08	10.60	655.95	3.45
				2 yarns	9	3.46	33.83	1866.56	9.82
				3 yarns	12	4.59	34.23	1420.13	7.47
				4 yarns	16	6.11	103.12	3211.25	16.90
				5 yarns	19	7.24	197.51	5180.69	27.27
				6 yarns	20	7.63	263.57	6562.45	34.54

Table 5.

Shear results of E-glass fabrics on pull-out test

Fabric type	Fabric direction	Fabric width (cm)	Fabric length (cm)	Ends of yarn	Shear displacement		Shear force (N)	Shear rigidity (N/m °)	Specific shear rigidity
Fabric type	Fabric direction	Fabric width (cm)	Fabric length (cm)	Ends of yarn	(mm)	(°)	Shear force (N)	Shear rigidity (N/m °)	(N/m° g.m⁻²)
E-glass	Warp	30	10	1 yarn	3	1.18	0.67	108.81	0.14
				2 yarns	4	1.55	1.20	148.25	0.19
				3 yarns	3	1.18	2.01	344.34	0.43
				4 yarns	10	3.84	2.28	113.40	0.14
				5 yarns	10	3.85	6.04	299.04	0.37
				6 yarns	8	3.09	12.88	796.72	0.99
				7 yarns	9	3.47	9.12	501.86	0.63
	Warp	30	20	1 yarn	4	1.56	1.34	163.75	0.21
				2 yarns	4	1.54	2.41	298.65	0.37
				3 yarns	4	1.56	4.29	525.96	0.66
				4 yarns	7	2.67	3.22	230.10	0.29
				5 yarns	8	3.08	22.96	1423.73	1.78
				6 yarns	6	2.32	16.25	1337.57	1.67
				7 yarns	8	3.04	26.45	1658.73	2.07

Table 3 shows the shear force angle curve for shearing the warps in the textured polyester fabric during the application of a tensile pulling force on the filling yarns. It was found that the shear force angle was proportional to the number of pulled ends. When the number of pulled ends increased, the shear force and shear angle also increased. In addition, when the fabric length increased the shear force also increased, but the shear angle increased only slightly. It was also observed that local yarn slippage occurred between the warp and filling in the interlacement region when the pulled yarn (filling) force was applied and rotated the perpendicular yarn (warp) in the plane of the fabric.

Table 4 shows the shear force angle curve for shearing the filling in the para-aramid (Twaron CT 714) fabric during the application of a tensile force to the warp yarns. The shear force angle was in proportion to the number of pulled ends – when the number of pulled ends increased, both the shear force and the shear angle increased. In addition, when the fabric length increased the shear force and the shear angle also increased.

Table 5 shows the shear force angle curves for shearing the filling in the E-glass fabric during the application of tensile pulling force to the warp yarns. It can be observed that the shear force angle and the number of pulled ends were proportional. When the number of pulled ends increased, the shear force and the shear angle each also increased. In addition, when the fabric length increased the shear force increased, but the shear angle increased only slightly.

Effect of sample dimensions and the number of pull-out ends

The shear force angle results for various fabric width/length ratios and the number of pull-out ends in textured polyester fabric are presented in Figure 5. As seen in Figure 5 and Table 3, when the number of pull-out ends increased the shear force angle values increased in each of the fabric width/length ratios, 3/1, 1.5/1, and 1/1. In addition, as the fabric width/length ratios decreased, the shear force angle values increased due to the increasing number of sheared warp ends. The shear force angle results for various fabric width/length ratios and the number of pull-out ends in para-aramid (Twaron CT 714) fabric are presented in Figure 6.

Figure 5.

Relationship between shear force angle and the number of pulled ends for various fabric lengths in polyester fabric (fabric width: 30 cm).

Figure 6.

Relationship between shear force angle and the number of pulled ends for various fabric lengths in Twaron CT 714 fabric (fabric width: 30 cm).

It is seen from Figure 6 and Table 4 that when the number of pull-out ends increased, the shear force angle increased slightly in each of the fabric width/length ratios, 6/1, 3/1, 1.5/1, and 0.86/1. The increase in shear force angle values in fabrics of width/length 1.5/1 and 0.86/1 was, however, higher than those for 6/1 and 3/1. In addition, as the fabric width/length ratios decreased, the shear force angle increased due to the increasing number of sheared warp ends.

The shear force angle results for various fabric width/length ratios and the number of pull-out ends in E-glass fabric are presented in Figure 7. As seen from Figure 7 and Table 5, when the number of pull-out ends increased, the shear force angle values increased in either of the fabric width/length ratios, 3/1 or 1.5/1. However, the fabric shear angles in fabric width/length ratio 3/1 were slightly higher then those for ratio 1.5/1. This was because it was easy to rotate a smaller number of filling yarns in the plane of the fabric. On the other hand, when the fabric width/length ratios decreased, the shear force values increased due to the increased number of sheared filling ends.

Figure 7.

Relationship between shear force angle and the number of pulled ends for various fabric lengths in E-glass fabric (fabric width: 30 cm).

During the fabric shearing in the yarn pull-out test it was observed that the para-aramid sample having a high fabric width/length ratio (3/1) and 7 or more pulled ends had a mixed region at the end of the fabric, illustrated in Figure 8. The region around the pulled yarns showed a small-scale crimp extension of different lengths during the fabric shearing stage (fabric displacement).

Figure 8.

Mixed region of shear (fabric displacement) and crimp extension during pull-out test in Twaron CT 714 fabric.

Shear rigidity results

Fabric shear rigidity on each of the low modulus polyester fabric, high modulus para-aramid and E-glass fabrics was found to be based on the relationships defined in the shear force/angle relationship sub-section of the text.

In the case of textured polyester fabric the shear rigidity results for various fabric width/length ratios and the number of pull-out ends are presented in Figure 9. Figure 9 and Table 3 demonstrate that as the number of pull-out ends increased, the shear rigidity values increased in each of the fabric width/length ratios, 3/1, 1.5/1, and 1/1. In addition, as the fabric width/length ratios decreased, the shear rigidity values increased due to the increasing number of sheared warp ends. This indicated that there was a proportional relationship between shear rigidity and the number of pulled ends.

Figure 9.

Relationship between shear rigidity and the number of pulled ends for various fabric lengths in polyester woven fabric.

The shear rigidity results for various fabric width/length ratios and the number of pull-out ends in para-aramid (Twaron CT 714) fabric are presented in Figure 10. Figure 10 and Table 4 show that as the number of pull-out ends increased, the shear rigidity values increased slightly for fabric width/length ratios 6/1 and 3/1, but increased sharply at fabric width/length ratios 1.5/1 and 0.86/1. The increase in shear force angle values in fabric width/length ratios 1.5/1 and 0.86/1 was also high compared to those for ratios 6/1 or 3/1. In addition, when the fabric width/length ratios were decreased, the shear rigidity values increased due to the increasing number of sheared warp ends. This indicated that fabric sample dimension with a low width/length ratio and the number of pulled ends had a strong influence on fabric shear rigidity.

Figure 10.

Relationship between shear rigidity and the number of pulled ends for various fabric lengths in Twaron CT 714 fabric.

Shear rigidity results for a range of fabric width/length ratios and the number of pull-out ends in E-glass fabric are presented in Figure 11. It is seen from Figure 11 and Table 5 that as the number of pull-out ends increased, the shear rigidity values increased in both fabric width/length ratios, 3/1 and 1.5/1. On the other hand, in the case of the fabric width/length ratio 1.5/1 the shear rigidity values increased sharply as the number of pulled ends increased. This was probably due to the increasing the number of sheared filling ends.

Figure 11.

Relationship between shear rigidity and the number of pulled ends for various fabric lengths in E-glass woven fabric.

Specific shear rigidity was calculated in low modulus polyester fabric, high modulus para-aramid and E-glass fabrics based on the relationships defined in the shear force/angle relationship sub-section of the text. As seen from Figure 12 and Tables 3, 4 and 5, as the number of pull-out ends increased, the specific shear rigidity values slightly increased in the polyester and E-glass fabrics. In contrast, the increase in specific shear rigidity in Twaron CT 714 was high, and reached a maximum value at 8 yarn ends.

Figure 12.

Relationship between specific shear rigidity and the number of pulled ends for various woven fabric types (fabric width: 30 cm, fabric length: 20 cm).

Shear jamming results

Shear jamming results for various fabric width/length ratios and the number of pull-out ends in textured polyester fabric are presented in Figure 13. It is seen from Figure 13 and Table 3 that as the number of pull-out ends was increased, the shear angle values increased in each of the fabric width/length ratios, 3/1, 1.5/1, and 1/1. The minimum shear angle resulted when the number of pulled ends was 1 and the maximum shear angle when the number was 5. The shear jamming angle ranged from 1 to 13°, and the difference between shear jamming angles was around 12°.

Figure 13.

Shear angle jamming in polyester woven fabric for various fabric lengths (pulled ends: 1–5).

The shear jamming results for various fabric width/length ratios and the number of pull-out ends in para-aramid (Twaron CT 714) fabric are presented in Figure 14. As seen from Figure 14 and Table 4, when the number of pull-out ends increased, the shear angle values increased in each of the fabric width/length ratios, 6/1, 3/1, 1.5/1, and 0.86/1. The shear jamming angle ranged between 1.5° to 9.9° and the difference between shear jamming angles was around 8.4°. The minimum shear angle occurred when the number of pulled ends was 1, and was at a maximum when the pulled ends were between 6 and 9. It was also observed that a small amount of wrinkling occurred in the clamp region of the fabric sample when the width/length ratio was a minimum and the pulled ends were at a maximum.

Figure 14.

Shear angle jamming in Twaron CT 714 woven fabric for various fabric lengths (fabric length 5 cm, pulled ends: 1–9; fabric length 10 cm, pulled ends: 1–6; fabric length: 20 cm, pulled ends: 1–8; and fabric length: 35 cm, pulled ends: 1–6).

Shear jamming results for various fabric width/length ratios and the number of pull-out ends in E-glass fabric are presented in Figure 15. It can be seen from Figure 15 and Table 5 that as the number of pull-out ends increased, the shear force angle values increased at fabric width/length ratios of 3/1 or 1.5/1. The minimum shear angle was obtained when the number of pulled ends was 1, whereas the maximum shear angle occurred when this number was 7. The shear jamming angle ranged from 1° to 3.47°, and the difference between shear jamming angles was around 2.29°.

Figure 15.

Shear angle jamming in E-glass woven fabric for various fabric lengths (pulled ends: 1–7).

The shear results from the yarn pull-out method may be used when considering the formation of fabrics for either soft or rigid technical textile applications. For instance, local fiber angular distortions could be predicted during the shaping of the fabric by molding, especially in those with complex curved geometry. In addition, shear by pull-out can provide some idea of the capability of high modulus fiber base dry fabric stitching, folding, and shaping when applying three-dimensional garment and fabric shear.

Conclusions

The results generated from this study show that the yarn pull-out test is suitable for measuring fabric shear. Various fabric types were tested to define fabric shear by this method. Fabric shear in general depends on fiber modulus, yarn linear density, fabric density, fabric interlacement, and yarn or fabric surface finish. During shear testing by pull-out it was found that fabric width/length ratio and the number of pull-out ends were important parameters.

Shear strength increased as the fabric width/length ratio decreased, but increased as the number of pulled ends increased. Fabric width/length ratio and the number of pull-out ends influenced fabric shear rigidity. In general, as the number of pull-out ends increased, shear rigidity also increased. On the other hand, as the fabric width/length ratios decreased, shear rigidity again increased. The number of pull-out ends and the fabric width/length ratios are therefore seen to influence fabric shear rigidity.

Shear jamming angles were found to be a feature of the number of pulled ends. The maximum and minimum shear angles were generated by 5–9 and 1 ends, respectively. On the other hand, local fabric shearing properties could be identified by pulling the ends in various regions of the fabric, which was especially important for fabric handling during formation. It was concluded that the pull-out method is a simple way to define general and local fabric shear properties for a range of end-uses.

Footnotes

Funding

This research received no specific grant from any funding agencies in the public, commercial, or not-for-profit sectors.

Acknowledgements

This study was supported in part by Erciyes University Scientific Research Unit (EUBAP), contract number EUBAPFBA–10–2882, and the author is grateful to the Scientific Research Department of Erciyes University for this invaluable support.

The author would also like to thank Miss Gaye Yolacan for her support during this project.

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