Yarn and fabric testinng

1. STIFFNESS/ DRAPE
BY
MANDAR S.KULKARNI
D.K.T.E.SOCIETY’S
TEXTILE AND ENGINEERING INSTITUTE,
ICHALKARANJI
AN AUTONOMOUS INTITUTE

2. Terms and Definitions
 Handle: The feel of the material which qualitatively includes the
terms such as stiff, limp, hand, soft, rough and smooth.
 Flexibility: Ease with which a specimen may be bent. In certain
cases, the weight of material acts to bend it about an axis.
 Rigidity: Measure of resistance offered by the specimen to
bending. ( Measure of Stiffness)
 Drape: Ability of a fabric to assume graceful appearance in use.
Natural falling ability of the fabric because of its own weight.
drape differ from rigidity in that, the weight of the material
influences a deformation at some angle to the line of action.

3. Fabric Stiffness Measurement-Shirley stiffness
tester
 Principle –It works on Cantilever Principle
 Concept of Overhanging Length and Bending Length.
L= Length of Fabric Projecting
θ= Angle through which the Fabric Bends.
M = Mass per unit area of the fabric=mg/cm2 = e.g.1350 mg /100cm2 =13.5 mg/cm2

4. Fabric Stiffness
L = Overhanging length for any angle of droop. ( will vary with angle of droop)
Warp way Lwarp =6 cm
weft way Lweft =5 cm
C = Bending Length = Length calculated by considering angle of droop.
C =L [
cos(𝜃/2)
8𝑡𝑎𝑛𝜃
]1/3
--------(*)
For Angle of droop 7.10 degree C =L
For Angle of droop 41.5 degree C= L/2 = 3cm warp / 2.5 cm weft
Cwarp, Cweft respectively are the warp and weft bending lengths

5. Flexural Rigidity
Flexural Rigidity :It is the ratio of small change in bending
moment per unit width of the material to the corresponding
small change in curvature.
Flexural rigidity = G = M X C3 mg/cm2 xcm3
M= fabric mass per unit area=13.5 mg/cm2
Gwarp = 13.5 x(3)3 =13.5x27
=364.5 mg-cm
Gweft = 210.93 mg-cm
Overall flexural rigidity = 𝐺𝑤𝑎𝑟𝑝𝑥𝐺𝑤𝑒𝑓𝑡 mg-cm
= 277.27 mg-cm

6. Bending modulus :The stiffness of a fabric in bending is dependent on its
thickness, the thicker the fabric, the stiffer it is if all other factors remain
the same.
The bending modulus independent of the dimensions of the strip tested so
that by analogy with solid materials is a measure of 'intrinsic stiffness’.
Bending modulus = (12XGX10−6)
𝑇3
= 12 𝑥277.27𝑥10−6
0.04 3
= 83.18 kg/cm2
 T=Thickness of fabric in cm,
 here T= 0.4 mm =0.04 cm

7. Shirley Stiffness Tester

8. Heart loop method
l
L=15cm
Heart loop test is applicable to fabric which are very limpy as well as to knitted fabric
which undergo multidirectional bending.

9. Hanging loop method
L= Specimen Length
l= Length of loop hanging under its own weight
lo = Undistorted Length of Loop = 0.1337x L
Stiffness ( d ) = l-lo
Bending Length ( C ) = lo x f(ꝋ) ; ꝋ = 32.85 x (d/lo)

10. Factors affecting fabric stiffness
 1. Yarn twist :
 The fabric stiffness increases with increase in yarn twist
 2.Fabric cover:
 The stiffness of fabric increases with increase in cover factor. At same number of warps/inch if
the number of picks/inch are increased the stiffness value increases.
 3.Fabric thickness:
 As mentioned in the formula the higher the thickness higher will be the stiffness
 4.Fabric weave:
 The stiffness of plain weave fabric is high in comparison with that of twill and sateen.
 5.Effect of resin treatment:
 The stiffness of resin treated cotton fabric increases in comparison with that of untreated
fabric


11. Drape
 The draping qualities required from a fabric will differ completely
depending on its end use, therefore a given value for drape
cannot be classified as either good or bad.
 Knitted fabrics are relatively floppy and garments made from
them will tend to follow the body contours. Woven fabrics are
relatively stiff when compared with knitted fabrics.
 Measurement of a fabric drape is meant to assess its ability to do
this and also its ability to hang in graceful curves.

12. Cusick drape test-Works on parallel light principle
 A circular specimen of 10 inch diameter is supported on a circular disc of 5 inch
diameter. The unsupported area drapes over the edge. The specimen like gramophone
recorder no drape. The area projected is equal to the gramophone disc.The fabric
showing drape will give lesser area depending on the fall which is shown below

13. Cusick drape test

14. Cusick drape test
Projected Area of draped Sample
Drape Coefficient = ----------------------------------------------
Theoretical Maximum Projection Area
mass of shaded area
Drape coefficient = ---------------------------- X 100%
total mass of paper ring
drape.swf =
𝐴𝑠
−𝐴𝑑
𝐴𝐷
−𝐴𝑑
x 100
Where As =Actual projected area of the specimen
AD = The area of specimen
Ad =The area of supporting disc

15. Factors Affecting Drape
 Fibre , Yarn and Fabric Stiffness
 High twist, more stiff, less drape.
 Fabrics with long float, more flexible.
 Chemical Finishes modify hand of fabric.