158
CHAPTER 8
MEASURING FABRIC HAND
8.1
INTRODUCTION
Fabric hand is a generic term for the textile sensation occurring
when fabrics are handled, and consumer preferences for textile products are
greatly influenced by this property. In the case of weft-knitted fabrics, it is
essential that they have a soft feel so that they do not cause any irritation
to the skin. For an outerwear knitted fabric, a soft feel is necessary and a
good bulk is also required. Realizing the importance of this property,
Common Wealth Scientific Industrial Research Organisation (CSIRO)
Australia, carried out a study on the prickliness of knitted fabrics. It is also
customary to use the outerwear fabric without the inner garment, and in
such circumstances the handle of the garment is an important property.
Although fabric hand can be judged by human hand subjectively,
it is necessary to evaluate it objectively. Among the objective methods, the
best known is the Kawabata Evaluation System or KES. However, the
KES-F method has not so far been commercially accepted on a wide scale.
The procedures are rather cumbersome and time-consuming and the
instruments are expensive. Other attempts at quantifying fabric hand have
also been rather complicated and involve measurement of several
parameters. A simple, inexpensive and reliable objective method to judge
fabric hand is needed. If such a method proved itself, it could be accepted
in commerce as an invaluable screening tool or as a standard method.
159
At present, there is a need for the objective evaluation of the
fabrics to produce quality fabrics to compete in the International market.
Particularly, in knitted fabric, objective evaluation has been done to a very
limited extent. KES-F (Kawabata Evaluation System for Fabric Evaluation)
and FAST (Fabric Assurance by Simple Testing) techniques are available for
objective evaluation of the fabric handle. They are very rarely used in
commercial practice due to the practical difficulty of their cumbersome
testing procedures, and very high cost of the instruments. From the
seventeen mechanical properties obtained from the KESF system, specific
aspects of handle such as stiffness, softness and crispness, can be obtained
by the regression equations, which give relationship between the mechanical
properties such as bending, shear, tensile, compression, and surface
roughness of the fabric. The constants for these equations, i.e., the emphasis
given to individual fabric parameters vary by fabric end use, whether for
summer or winter or by country. Over the course of time, the use of these
derived handle value has declined in favour of a fingerprint of the seventeen
fabric mechanical parameters used to characterise each fabric.
Considerable amount of research is currently in progress to
quantify fabric handle by simple methods. Various handle measuring devices
available are Thwing-Albert/Clupak Fabricometer (1970) and Handle-OMeter, and the King fabric stiffness tester. The Fabricometer is based on the
principle of pulling a fabric through a ring which provides a measure of
fabric handle. Usually a fabric disc sample is held in the centre and
extracted through a device installed on a Instron tensile tester. A load
displacement of the type shown in Figure 8.1 is obtained. One character on
the curve, such as the peak value (e.g., ASTM D4032-82) or the slope at a
certain point of the curve is then selected as the quantitative representation
of fabric handle. The simplicity and convenience of this approach is obvious.
Yoon et al., (1984) have offered some data on the handle modulus of knitted
fabric made from polyester/cotton blends. It is pertinent to note that these
authors have used the NASA method (Alley and McHatton, 1976). Many
160
Withdrawal
Figure. 8.1
displacement (cm)
Typical load-displacement curve
during the withdrawal of fabric
through the ring ( Source : Grover
Sultan and Spivak ,1993).
161
workers have developed a test method to measure fabric handle based on
similar principles. Pan and Yen (1992) and Behery (1986) have carried out
extensive work on the fabric extraction method. Behery (1986) investigated
the
relationship
of withdrawal
force
measurements
with
KESF
measurements using a nozzle with conical geometry. He found that this
withdrawal force measurements correlated well with KESF hand values.
Pan Ning and Yen (1992) have made indepth studies on the load
displacement curve obtained, and also have been concerned with the
theoretical prediction of the extraction force based on the fact that the fabric
is considered as equivalent to a homogeneous membrane. They have
proposed a detailed methodology to interpret handle force. In another paper,
Pan and Yan Haojing (1986) have discussed a new measurement proposal
for fabric hand evaluation, which is based on pattern recognition method.
By virtue of the theory of pattern recognition combined with the calculating
methods for hand values of a fabric, a new proposal and an instrumental
system monitored by a microcomputer are suggested to compute fabric hand
measurement and evaluation. A hand pattern curve WD value as well as the
primary hand values of a fabric can be provided automatically and promptly.
The following Table 8.1 shows details of the extraction method, the number
of fabrics studied, and the results obtained to know the potential of the
method.
8.2
APPARATUS
A simple apparatus (Fig.8.2), designed for this method, was used
for determining the handle force. The apparatus consists of a spring balance
(S), a highly polished stainless steel bush (B) attached to a platform (P), and
motor (M) to move the bush from top to bottom over the fabric specimen of
25cm diameter. A steel wire is attached to the spring balance, and this
passes through a bush made of highly polished steel. The inner hole radius
of the cylindrical bush was varied from 18mm to 28mm radius to suit the
various types of weft-knitted fabric. Various diameters were selected on the
162
Table 8.1
Year
Details of fabric extraction method
Author(s)
Reference
Details of fabrics
examined
Remarks
1976 Alley and
McHatton
Conical Nozzle
Films, laminates
and composites
1980 Alley
Conical Nozzle
Membrane forces
on the fabrics.
1981 Behery and
Monson
Nozzle r0=minimum
radius of nozzle=0.3
cm for small nozzle
and 0.5 cm for large
nozzle r0=reference
radius=0.714 cm and
B=one half cone
included angle, 0.393
rad
145 fabric samples Correlation of
Physical test
measurement and
initial modulus was
good. Instron has
been used.
A linear decrease in
1984 Yoon, Sawyer Conical nozzle method Single Jersey
and Buckley of Alley and McHatton fabrics made from handle modulus with
P/C blends
(1976)
increase in cotton
content was
observed. A value of
handle modulus less
than one is
considered to be
acceptable.
1992 Pan and Yen
R„ = 51 mm
D = 24.5 mm
Conical Nozzle
48 medium
thickness suiting
fabrics
Measurement of
extraction curve and
dividing into 5
geometric features.
Instron has been
used.
1993 Grover,
Sultan and
Spivak
Cylindrical ring of
highly polished steel, 2
cm in diameter and 2
cm height.
11 shirting fabrics,
unlaundered and
silicone treated
laundered and
silicone treated.
Polyethylene glycol
finish.
Handle force. Good
correlation between
handle force and
KESF parameters.
Details of tester
undisclosed.
163
Figure. 8.2 Specific Handle force tester.
164
basis of the thickness of the knitted fabrics (Table 8.2), and were used in the
evaluation.
As the hole radius changes, the hole inside surface area (A cm2)
will change which, in turn, will affect the value of the fabric hand force (F)
as the frictional area between the withdrawn fabric and the hole will
change. Thus for obtaining a comparative fabric specific handle force (SHF)
irrespective of the sample thickness, the hole surface area (A), the fabric
handle force (F) must be divided by the packing fraction (B), and the area
(A cm2). Therefore the specific handle force is obtained from the equation as
given below :
SHF =
F
—
A.B
g/cm2
...(8.1)
The packing fraction (B) has been defined as the ratio of the
maximum fabric material volume to the inside ring hole volume.
Therefore
2jt(R-H/2)H.W/p
B
=
-----------------------it Rh2H
2R-H
p
W
R,,2
where
R =
... (8.2)
Fabric Specimen of radius 12.5cm.
Rh
H
W
=
=
=
the chosen hole radius in cm.
the hole height 2cm.
the fabric weight in g/cm2.
p
=
the fibre density in g/cm:i
... (8.3)
165
Table 8.2
Nozzle selection based on the fabric thickness
• Thickness Range (cm)
0.015-0.025
Nozzle dia (mm)
0.025-0.035
14
16
0.035-0.045
18
0.045-0.055
20
0.055-0.065
22
0.065-0.075
24
0.075-0.085
0.085-0.095
26
28
0.095-0.105
30
166
This method of normalising handle has been suggested by Pan
Ning (1995). It is to be noted that this represents a better measure of the
specific handle force (SHF) than the method followed by Grover et al.,
(1993). The cylindrical bush was well cleaned with methyl alcohol before a
test was done. The platform, in which the stainless steel bush is mounted,
was moved by a motor and the peak load registered by the spring balance
was noted. The maximum load reached on the spring balance was noted
down and the mean of 20 readings was taken side by side. Figures 8.3 and
8.4 show the apparatus used in the study.
The forces involved in the initial deformation are related to the
bending modulus and the shear stiffness of the fabric. The compression and
fabric friction play a larger role as the fabric specimen is squeezed to the
dimensions of the ring. Fabric withdrawal force depends on the resistance
to bending, shear, compression and sliding force. The force generated
depends not only on the fabric properties, but also on the ring size, and
sample size. The maximum withdrawal force can be taken as a measure of
fabric handle force (Table 8.3). Its correlation with mechanical properties
obtained by the KESF has been listed for knitted fabrics (Table 8.4).
8.3
RESULTS AND DISCUSSION
In Table 8.3 are included the specific handle force of all the weft-
knitted fabric samples. It is interesting to note that the specific handle force
of knitted fabrics shows a lower value on the technical back side compared
to the technical front side; this is due to the structural differences existing
between the two sides. Fabric bends easily on the backside owing to the
nature of the loops, and this is the reason for the lower value. When a plain
weft-knitted fabric is bent wale way face side, the limbs of the loops bend
gradually, and this is stiffer. When the knitted fabric is bent wale way back
side, the structure bends easily due to hingeing. This difference is noticed
in all the fabric samples, regardless of single or double jersey structures.
167
Table 8.3
SI.
No.
Handle Force tester value
Fabric
Code
Face
Back
SHF Nozzle Thickness
Mean kg/cm2
Dia mm
cm
Kg
SD
Kg
SD
2.994
2.578
2.659
2.756
2.778
2.531
0.301
0.264
0.208
0.128
0.155
0.286
2.665
2.225
2.411
2.353
2.375
2.063
0.304
0.202
0.300
0.208
0.162
0.156
2.830
2.402
2.535
2.555
2.577
2.297
0.890
0.861
0.938
0.891
0.921
0.828
18
18
18
18
18
18
0.04399
0.03858
0.03739
0.03967
0.03871
0.03840
1.156
1.344
1.406
1.088
1.256
1.475
0.120
0.133
0.088
0.103
0.131
0.210
0.981
1.306
1.169
0.95
1.156
1.331
0.139
0.153
0.069
0.020
0.139
0.139
1.069
1.325
1.288
1.019
1.206
1.403
0.286
0.380
0.357
0.298
0.356
0.404
20
20
20
20
20
20
0.05163
0.04813
0.04991
0.04724
0.04680
0.04801
1.369 0.136 1.083 0.072 1.226
1.245 0.270 1.167 0.101 1.206
0.358
0.356
20
20
0.04731
0.04693
2.819
1.950
1.259
1.444
1.588
0.234 2.521 0.483 2.670
0.125 1.925 0.197 1.938
0.053 1.225 0.113 1.242
0.111 1.269 0.134 1.357
0.072 1.469 0.062 1.529
0.555
0.555
0.365
0.502
0.295
26
20
20
18
24
0.06655
0.04826
0.04704
0.03739
0.07163
2.215
2.988
1.756
2.150
1.406
0.383
0.394
0.294
0.050
0.171
2.120
2.744
1.800
2.094
1.372
0.414
0.515
0.282
0.443
0.238
24
24
26
22
26
0.07087
0.07371
0.08824
0.06541
0.07960
1.925 0.032 1.794 0.278 1.860
1.606 0.113 1.438 0.108 1.522
2.413 0.084 1.953 0.321 2.183
0.321
0.243
0.370
26
28
26
0.08014
0.08646
0.08166
GROUP A
1.
2.
3.
4.
5.
6.
1
2
3
4
5
6
GROUP B
7.
8.
9.*
10.
11.
12.
7
8
9
10
11
12
GROUP C
13.
14.
13
14
GROUP G
15.
16.
17.
18.
19.
29
30
31
32
33
GROUP H
20.
21.
22.
23.
24.
34
35
36
37
38
2.025
2.500
1.844
2.038
1.338
0.115
0.127
0.184
0.113
0.126
GROUP I
25.
26.
27.
39
40
41
Table 8.4
Correlation between SHF and KES-F parameters
KES-F
parameters
SHF
EMT (%)
-0.5056
LT
WT (J/m2)
0.2700
-0.4789
RT (%)
-0.2678
B (pN.m)
-0.2952
2HB (mN)
-0.2458
G (N/m)
0.1472
2HG (N/m)
0.3029
2HG3 (N/m)
0.2766
MIU
-0.5805
MMD
0.3193
SMD (pm)
WC (J/m2)
-0.2153
LC
-0.3334
RC (%)
-0.6431
T (mm)
W (mg/cm2)
-0.4986
-0.2605
-0.4407
Fig.8.3 Working principle of specific handle force tes
Fig.8.4 Working principle of
specific handle force t
171
This is certainly advantageous to the body as the back side of single jersey
is in contact with the skin. This difference displays structural dichotomy.
Compared to the fabric sample 6, all the other samples show somewhat
higher values implying that these are stiff. This clearly demonstrates that
direction of yam twist, and the combinations of feed have an effect on the
specific handle force. Fabric sample 3 is characterised by a high value, and
vt
it may be^called that this is produced by the feeder arrangement of SS/Z.
In the case of Group B, there is a tendency for the specific handle
force to increase with increase in tightness factor; this is clearly noticeable
in samples 10 to 12; this is easily understandable as the structure becomes
tight with a decrease in loop length. The other reasons are the increase in
bulk density of weft-knitted fabrics.
As regards the two fabric samples knitted from carded and combed
qualities, the handle values are equivalent (Group C).
In Group G which comprises commercial single-jersey fabrics, the
handle values range between 0.295 to 0.555. Fabric sample 33 displays an
exceptionally low value.
Specific handle values of commercial double-jersey fabrics, display
some interesting results. Of all the samples, fabric sample 38, which is
interlock, shows a lower value.
Fabrics included in Group I show a better value in fabric
sample 40.
The variation in handle force between technical face and back sides
of a series of weft-knitted fabric shows that there is no consistency between
single and double jersey fabrics. One would expect the single jersey fabrics
to exhibit a wide variation in view of their structural differences rather than
172
the double jersey structure. That this is not so is evident from the values
included in Table 8.3. The fact that fabrics included in Group H which
belong to double jersey category, also display differences between technical
front and back sides (ie., cylinder and dial side) raises some important
questions about the structure of these fabrics. By far, the carded sample 13
displays an exceptionally high value of 20% in the handle force between the
technical front and back sides, and this probably shows the yam effect. In
contrast, the combed fabric shows a low value evidently due to its soft
nature.
8.4
CORRELATION BETWEEN SPECIFIC HANDLE FORCE
AND MECHANICAL PROPERTIES OF WEFT-KNITTED
FABRICS
It will be interesting to find out the relationship between specific
handle force of a set of weft-knitted fabrics with the mechanical properties
of fabrics obtained from KES-F. Since the specific handle force encompasses
bending, shear, compression and surface properties, the correlation will be
of interest. Table 8.4 shows the correlation coefficients obtained. It may be
noted that Behery (1986) investigated the relation between the withdrawal
force measurements and KES-F values. He demonstrated that the
measuring of fabric hand by withdrawing the fabric through a ring could be
considered as a useful quantitative test for fabric hand. Pan et al., (1993)
proposed an overall evaluation of fabric performance by representing the
relevant fabric properties in a circular diagram as a "finger print" or
characterize fabrics for various applications. He used the Instron tensile
tester for testing the fabric properties rather than the KES-F and FAST
systems.
Table 8.4 gives the correlation coefficient between the specific
handle force and the mechanical properties for 27 fabric samples.
173
Table 8.5
Correlation matrix for SHF, Bending, Drape and Shear
SHF
(kg)
SHF (kg)
Bending rigidity (pN.m)
Drape (%)
Shear (N/m)
1
Bending
rigidity
(pN.m)
0.2735
-
1
Drape
(%)
0.1266
-
0.6330
1
Shear
(N/m)
0.2830
-
0.0886
-
0.2041
1
174
Some of the correlations, which appear to have some significance,
are between WT, SHF and WC, RC, MIU and thickness; the other
correlations are weaker.
This may be due to the highly deformable nature of the weftknitted fabrics unlike the woven fabrics. Due to curling tendency of the
weft-knitted fabrics even after finishing them, the values of the specific
handle forces may not be precise. These are some of the reasons for not
obtaining a good correlation between the handle force and the mechanical
properties.
Table 8.5 gives the correlations between the specific handle force
and the flexural rigidity values obtained by the cantilever bending tester,
and shear rigidity by Kilby’s (1963) method.
8.5
CONCLUSIONS
The following conclusions may be drawn from the above study.
1)
Specific handle force is found to be different for the technical front
and back sides of the weft-knitted fabrics, regardless of the
structure.
2)
The correlation between the specific handle force and the
mechanical properties is found to be rather weak.
3)
The correlation between the specific handle force and shear and
drape parameters is also weak.