33 Testing for woven fabrics – handle properties

R. Sukanya Devi

epgp books

 

 

Introduction:

 

Fabric handle as the name itself implies, is concerned with feel of the material and so depends upon the sense of touch. It compresses appearance and comfort. Fabric handle is a subjective phenomenon because it differs from person to person and it’s a challenge to predict it.This is evaluated by consumers and textile producers subjectively by means of his hand touch of the fabric from mechanical comfort view point. Subjective method is the most direct method to measure fabric handle but it restricts scientific understanding.Different types of material will have different degree of smoothness or roughness when the fabric handle is to be judges the sensation for stiffness , hardness or softness, roughness or smoothness are all made use of. Thus to overcome the disadvantage of subjective measurement and also to have theoretical understanding of fabric handle objective measurement is done.

 

Parameters Influencing Fabric Hand:

 

There below are few parameters that have a greater influence on fabric handle:

 

Weight and density: Weight per unit area (GSM) or unit volume is considered. If the fabric weight is high it will be hard to feel as compared to low weight fabric. Density measures the compactness or relaxation of fabric. It the thread density in the fabric is more it will be more compact when compared to low density. This contributes to the fullness of the fabric

 

Surface friction: It refers to resistance to be slipping either on the finger or on another piece of fabric. For balanced fabric surface friction should be adjustable. Otherwise it will create problem during processing and using. Fabrics vary in surface friction from harsh to slippery. Sensation of the fabric like smoothness and roughness is contributed by the surface friction.

 

Flexibility: It refers case s of squeezing of a fabric. Fabrics vary in compressibility from pliable to stiff. Drapability and crispness is influenced by this property. Depends on fibre property of the fabric

 

Compressibility: It refers case of squeezing of a fabric. Fabrics vary in compress ability from soft to hard.

  • Where,
  • M = Mass per unit area (g/m2)
  • G = Flexural rigidity.
  • C = Bending length (mm)
  • θ = Angle fabric bends
  • at θ = 7.1º, X = 1
  • Higher the bending length, stiffer is the fabric.
  • θ = 7.1º, C = L (mm)

So, pierce definition of bending length is “the length of rectangular strip of material which will bend under its own mass to an angle of 7.1º.

 

200mm x 25mm specimen strip dimension.

 

Allowing this strip to bend to a fixed (41.5º) under its own weight.

 

The over changing length is twice the bending length (C = L/2) at θ = 41.5º, X = 0.5.

 

Shearing and Drape

  • The ability of a fabric to deform by ‘shearing’ (so conform to the contours of the body) differentiates, it from other thin sheet materials such as paper or plastic film.
  • Difficult to measure, as textile materials are very flexible.
  • The term “Drape” used to describe the way a fabric hangs under its own weight determines how good a garment looks in use.
  • It differs from fabric to fabric and depends on end use.
  • A particular value cannot be classified as either good or bad.
  • The multi-direction curvature formed is dependent on shear property and bending stiffness.

Compression

  • Compressibility of fabric is defined as the extent or reduction in “Thickness” with the application of normal pressure.
  • During compression, the space between the fibres is decreased until they eventually come into contact with one another.
  • Changes within the structure causes by , (i)Bending of individual fibres(ii)Slippage between fibres/yarns.
  • Compression of fabric is completed in 3 stages,
  • Individual protruding surface fibres are compressed (by bending) [Elastic Deformation]
  • Inter yarn or inter fibre friction resist the slippage [Plastic Deformation]
  • Lateral compression of the fibres themselves [Elastic Deformation]
  • Measurements of thickness and compression properties of fabrics form an integral

part of objective evaluation of “Handle” properties of apparel fabrics.

  • During determination of the handle of fabrics, the fabric is compressed between the fingers.
  • Quality of a carpet or any other soft material is judged by testing the compressibility..

KAWABATA EVALUATION SYSTEM OF FABRIC (KESF):

 

Five different tests can be performed using KES for fabrics and the main mechanical characteristics produced, are described below

 

Modules of KES

  • 1. KES-FB1 – Tensile and shearing
  • 2. KES-FB2 – Bending
  • 3. KES-FB3 – Compression
  • 4. KES-FB4 – Surface friction and variation

Polar pairsand KES – F Parameters

 

The below table provides the polar pair of expressions related to fabric hand as a fabric physical property representing them as a subjective parameters vs objective parameters.

KAWABATA EVALUATION SYSTEM OF FABRIC (KESF) MODULES:

  1. KES-FB1 ® Tensile and shearing
  • Stressed up to 500gf/cm load
  • Sample is clamped between 2 Jaws with effective test area of 5/L cm x 20/W cm and subjected to a constant tension of 10gf/cm by a weight attached to the drum on which one jaw is mounted.
  • This type of biaxial extension ia called strip biaxial extension.
  • Constant tension is applied by allowing the drum to rotate freely.
  • The shear force is measured by a transducer connected to the other jaw which moved sideways to apply the shear deformation and the shear strain is detected by potentiometer.

For hand derivation, the warp and weft directional values are averaged

 

Parameters obtainted:

 

(a) WT = Tensile energy = Area under the load – extension

(b) Linearity (LT)

(c) Resilience (RT)

(d) Shear Rigidity G slope of curve between 0.5º and 2.5º shear Angle

(e) 2HG = Hysteresis of shear force at 0.5º shear angle

(f) 2HG5 = Hysteresis of shear force at 5.0º shear angl

 

KES-FB2 ® Bending

  • Fabric sample is bent between the curvatures –2.5 and +2.5cm-1
  • The stiffness(slope) and hysteresis are measured.

Parameters obtainted:

 

(g) B = Slope between 0.5 and 1.5cm-1 curvature

(h) 2HB = Hysteresis of bending moment at curvature 1cm-1.

  1. KES-FB3 ® Compression

The compressional properties between two plates and increasing the pressure while continuously monitoring the sample thickness up to a max. pressure of 50gf/cm2(0.49N/cm2).The constant velocity of 20 micro.m/s is maintained. The shape of the load thickness is similar to the shape of the tame ensile property curve, and the parameters are used with the identification of compression energy ,resilience and linearity of compression curve.

 

Compressional measurement is done by KES-F-3 as shown in Figure. The principle of the apparatus is shown in Fig. is an example of the recorded curves. The integration of the curve is computed by the computing block automatically.

 

The signal from the transducer is passed the filter having prescribed frequency response and integrated to compute SMD.

 

Parameters obtained:

 

(i) LC = Linearity of compression curve Area under compression curve / Area of triangle

(j) WC = Compressional enegy

(k) RC = Compressional resiliernce

  1. KES-FB4 ® Surface friction and variation

Surface geometry smoothness and frictional smoothness are measured. The sensors for these measurements shown in the figure. The contact surface of the frictional sensor is 10 parallel piano wires 0.5mm in diameter, and the surface shape is similar to that of a human finger print.A weight is used to apply 0.5 N contact force during measurement.The rough surface of fingerprint shape is sensitive to fabric surface roughness.

 

For geometrical smoothness sensor, single wire of the same diameter is used to measure geometry more accurately. The signals from these sensors pass a frequency filer with a second high-pass response. The sweep velocity is 1 mm/s. when we touch a fabric and sweep our finger across the fabric surface, the sweep velocity is normally 5 cm/s; that is 1 Hz in an actual sweep. A frequency component higher than about 250 Hz in an actual sweep is naturally eliminated by the fingerprint surface and the transducer mechanism. The most sensitive frequency range of human sensation is 50-200 Hz and a filter s used to deect only this range, eliminating the noise component from surface sensing.

 

The parameters representing surface properties are:

 

(l) MIU = mean value of coefficient of friction,(for a 2-cm return sweep)

(m) MMD = mean deviation of coefficient of friction

(n) SMD = Geometrical roughness

In addition to these, KES-F also measures following fabrics parametersalso,

(o)   W = fabric weight per unit area and

(p)   To = fabric thickness

 

FAST SYSTEM (FABRIC ASSURANCE BY SIMPLE TESTING)

 

It is much simpler than KESF system. The FAST system, developed by CSIRO for quality control and assurance of fabrics. FAST, or Fabric Assurance by Simple Testing, consists of a series of instruments and test methods which are inexpensive, robust and simple to use. It measures properties which are closely related to the ease of garment making-up and the durability of worsted finishing. FAST-1 gives a direct reading of fabric thickness over a range of loads with micrometre resolution. FAST-2 measures the fabric bending length and its bending rigidity. FAST-3 measures fabric extensibility at low loads as well as its shear rigidity. FAST-4 is a quick test for measuring fabric dimensional stability, including both the relaxation shrinkage and the hygral expansion.

  • 1) FAST 1 – Compression meter
  • 2) FAST 2 – Bending meter
  • 3) FAST 3 – Extension meter
  • 4) FAST 4 – Dimension stability test
  1. Dried at 105ºC and length (warp/weft) – L1
  2. Soared in water and wet relaxed length –L2
  3. Redried in oven and measure again – L3

Fast measuring parameters

 

The below table provides the parameters obtained from each module:

FAST – 1: Compression meter

  • This instrument measures fabric thickness at various loads and surface thickness
  • The fabric thickness at two different pressures enables the accurate measurement of surface layer thickness
  • Thickness is measured at a pressure of 2 gf/cm2
  • Surface thickness is the difference in thickness of a fabric measured at pressures of 2 gf/cm2 and 100 gf/cm2.
  • This gives information about the hairiness or surface bulk of the fabric (closely related to surface treatment like brushing, singeing)
  • Released surface thickness is the measure of the surface thickness after the fabric has exposed to steam or water

FAST – 2: Bending meter

  • This measures the fabric bending length according to BS 3356-1961.
  • The bending length is converted into bending rigidity, which is directly related to fabric stiffness – an important component of fabric handle
  • The operator error in aligning the sample is eliminated with the use of an optical sensor
  • The main problems associate with bending rigidity occurs in fabrics that have low values. These fabrics due to the ease with which they bend, would be difficult to handle and sew.
  • Fabric extensibility is combined with bending rigidity to give formability – a parameter related to the incidence of seam pucker

FAST – 3: Extension meter

  • This instrument measures fabric extension at various loads and bias extension
  • Extension is displayed as a percentage with a 0.1% resolution
  • Extensibility is measured at three loads 5 gf/cm (E5), 20 gf/cm (E20) and 100 gf/cm (E100).
  • The difference between E5 and E20 is used to calculate Formability
  • E100 is used in control chart (Fabric Fingerprint) as the measure of fabric extensibility. If the value is below approximately 2% then the fabric will be difficult to extend during seam overfeed.
  • Bias extension is converted to shear rigidity – which is directly related to fabric looseness – another important component of fabric hand
  • Shear rigidity below 30N/m, the fabric deforms so easily that it may give problems in handling, laying up and sewing.
  • Conversely if it is above 80N/m then the fabric can be difficult to overfeed, mould, etc.

FAST – 4: Dimensional stability test

 

•      This measures relaxation shrinkage and hygral expansion

•      The test is completed in less than an hour as compared to the conventional one-day test

•      A forced convection oven, a template and a ruler are the only equipment required to do the test

 

Advantages of FAST

 

•      FAST can tell one how well a fabric will perform

•      Abnormal FAST Fabric Fingerprints point to potential problem areas

•      Fabric Fingerprints can be used for

•      Fabric specifications

•      Developing new fabrics

•      Comparing fabric finishing routes

•      Assessing stability of finished fabrics

•      Predicting tailoring performance

•      Final garment appearance

 

Broad areas of Use of FAST:

 

•      I)Fabric Finishing (Using FAST-1):

•      Change in fabric surface characteristics after finishing process can be measured.

  • II) Tailorability:
  1. a) Formability and seam pucker (Using FAST-2 and FAST-3):
  • Sewing operations, especially those involved in overfeeding, imposes strains on the fabric.
  • Stiff fabrics resist buckling
  • Extensible fabric accommodate overfeed
  • b) Laying up and cutting (Using FAST-3):
  1. Very extensible fabrics, which move around while being cut, cause problems with sizing, pattern matching and sewing stage.

c) Sewing of long seams (Using FAST-3):

  1. Very extensible fabrics are difficult to match over a long seam length.

d) Steaming and pressing (Using FAST-4):

  1. Pressing operation rely on amount of fabric shrinkage
  2. Garment appearance is affected by fabric shrinkage

e) After care (Using FAST-4):

  1. Care must be taken when dealing with the fabrics which exhibits excessive shrinkage

f) Garment appearance (Using FAST-4):

  1. During conditions of high relative humidity, the onset of pucker can be attributed in part to increasing fabric dimension, i.e. hygral expansion.
you can view video on Testing for woven fabrics – handle properties

 

REFERENCES and URLs

 

  1. https://nptel.ac.in/courses/116102029/55
  2. https://nptel.ac.in/courses/116102029/56
  3. Saville,B.P,2004, comfort Physical Testing of Textiles, The Textile Institute, Woodhead Publishing Limited, Cambridge, England, pp 209-243
  4. Slater,K. 1986, The assessment of comfort, Journal of Textile Institute, 77(3), pp 157 – 171.