Stiffness Testing by Shirley Tester

In this article, we are going to know about the procedure of measuring fabric stiffness with Shirley stiffness tester. This process is followed in the lab and described here.

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Introduction

Stiffness is the property by which fabric resists deforming. Stiffness is a special property of the fabric. It is the tendency of the fabric to keep standing without any support. It is a key factor in the study of the handle and drape of the fabric.

Objectives of Fabric Stiffness Testing

To know about stiffness
To know about the stiffness tester
To know about the importance of stiffness test of fabric in textile.

Apparatus for Stiffness Testing

Stiffness tester
Scissor
Scale etc.

Working Principle of Stiffness Testing

A rectangle strip of fabric, (20 cm ✕ 2.5 cm) is mounted on a horizontal platform in such a way that it changes, like a cantilever, and bends downwards. From the length l and angle θ, a number of values are determined. The length of the fabric that will bend under its own weight to a determined, definite extent is called bending length. It is a measure of stiffness that determines draping quality. The calculation is as follows,

Stiffness (c) = lf (θ)
Where, f (θ) = (cos ½θ / 8 tanθ)⅓
If, θ = 41.5°, then f (θ) = ½

So, Stiffness (c) = lf (θ) = (l × ½) = ½

The stiffness of the specimen in the warp and weft way is usually tested. The relative humidity can affect the results, the test should be made in a standard testing atmosphere.

Atmospheric Condition

Dry bulb = 82
Wet-bulb = 79

So, From the chart Relative humidity = 66%

Figure of Shirley Stiffness Tester

Shirley Stiffness Tester

The tester is made of plastic. There is a template on the top of the machine. A scale is attached with the template. A mirror and an index line are adjusted in the machine. There are two side pieces that support the platform and the plastic place is inclined at 41.5°.

Working Procedure of Stiffness Testing

1. At first, cut the specimen warp and weft direction to size (20 cm ✕ 2.5 cm) with the aid of the template

2. Then both the template and specimen are placed on the platform where the fabric is underneath.

3. Now both are slowly pushed forward

4. The strip of the fabric will commence dropping over the edge of the template and the fabric is continued until the tip of the specimen viewed in the mirror cuts both index lines

5. The stiffness can immediately be read off from the scale mark opposite a zero line engraved on the side of the platform

6. Each specimen is tested 3 times

7. Finally, mean values for the bending length of warp and weft directions are calculated.

Fabrics for Stiffness Testing

Stiffness Testing Fabrics

Table 1: Determination of Fabric Stiffness (Warp-wise)

Serial no	Appearance	Sample length (cm)	Bending length (C= ½)	Average	Mean
1	Face right	2.5	1.25	1.42	1.55 cm= 15.5 mm
	Face left	3.15	1.575
	Back right	2.85	1.425
	Back left	2.85	1.425
2	Face right	3.15	1.575	1.6
	Face left	3.15	1.575
	Back right	3.25	1.625
	Back left	3.25	1.625
3	Face right	3.25	1.625	1.63
	Face left	3.3	1.65
	Back right	3.25	1.625
	Back left	3.25	1.625

Table 2: Determination of Fabric Stiffness (Weft-wise)

Serial no	Appearance	Sample length (cm)	Bending length (C=½)	Average	Mean
1	Face right	2.75	1.375	1.31	1.33 cm =13.3 mm
	Face left	2.8	1.4
	Back right	2.65	1.325
	Back left	2.25	1.125
2	Face right	2.85	1.425	1.3125
	Face left	2.80	1.4
	Back right	2.20	1.10
	Back left	2.65	1.325
3	Face right	2.75	1.375	1.363
	Face left	2.80	1.40
	Back right	2.65	1.325
	Back left	2.70	1.35

Calculation of Stiffness Testing

Flexural rigidity, G1 (Warp wise) = (MC³ ✕ 9.809 × 10^-6) µNm
= {240 ✕ (15.5)³ ✕ 9.809 × 10^-6}= 8.77 µNm
Flexural rigidity, G2 (Weft wise) = (MC³ ✕ 9.809 ✕ 10^-6 µNm

= {240 ✕ (13.13)³ ✕ 9.809 × 10^-6}= 5.33 µNm

Result

The fabric stiffness (bending) warp-wise is 15.5 mm

and the fabric stiffness (bending) weft-wise is 13.3 mm.

Conclusion

In this experiment, we knew about the procedure of determining fabric stiffness warp-wise and weft-wise and also knew about flexural rigidity. Fabric stiffness is one of the special properties of the fabric.