stretch recovery of knitted fabric

Ahsanullah University of Science and Technology
Department of Textile Engineering
Course No: Tex 400
Course Title: Project Work
Academic Semester: Spring 2018

Submitted by:
Name:Sanjoy Ray ID:13.02.06.107
Name:Ashek-uz-zaman ID:13.01.06.037
Name:Md. Abdus Sattar ID:13.01.06.168
Supervised by:
Mr. A. K. M. Mobarok Hossain Mr. A.N.M Masudur Rahman
Assistant Professor, DTE, AUST Assistant Professor, DTE, AUST

Study on elastic recovery of some common
single jersey structures knitted at different loop
lengths

Introduction
o Knitting is the second most popular technique of fabric or garment formation by
interlooping one or more set of yarn. The distinguished characteristics of knitted
fabric, when compared with woven, is mainly the elastic property. Knitted fabric
stretches considerably even under small stresses and recovers the original shape
following viscoelastic behavior.
o Most of the knit fabrics stretch in both direction i.e. length & width wise. However,
when weft knitted fabric is stretched along its width, it will stretch significantly. Along
its length, it will stretch slightly.
o In this project work elastic property, mainly elastic recovery, of different single knit
structures were studied numerically to have a knowledge on their stretch behavior.

Aim of this Project
To find out the influence of stitch length over stretch
recovery in knitted fabrics.
To determine the structural influence of some common single jersey
structures over their stretch recovery properties

Literature review
• Arnold et al Arnold et al analyzed on elastic recovery of cotton knitted fabrics. They found
that fabrics knitted from mercerized yarns had greater elastic recovery than those made from
the natural, and the fabrics knit of combed cotton yarn had greater elastic recovery than those
knitted with carded cotton yarn.
• Hazel et al analyzed different methods for measuring elastic Recovery of Plain, Rib and
Tricot knit fabrics. They found that in most cases elastic recovery determined by manually
applied loads was higher than that determined by the cyclic stress-strain curves.
• Witold Zurek et al carried out some experiments on the elastic properties of weft knitted
fabrics made of polyester and polyamide (twisted and textured) yarns. They found that all
fabrics showed widthwise higher elastic recovery. Moreover, polyamide knitted fabric
showed higher elastic recovery than polyester knitted fabric.

Extension:
Extension is the increase in length of a test specimen produced by a force as a
result of testing, expressed in units of length, millimeters.
Elongation:
Elongation is the ratio of the extension of the test specimen to its initial length. It
can be expressed as a percentage.
Let,
L=Initial length of the specimen
E =Extended length of the specimen after a specified force
Then, Elongation(%) =
E−L
L
× 100
Elastic limit
It is defined as the value of stress up to and within which the material returns back
to their original position (i.e. shape and size) on the removal of external force.
L
E

Un-recovered elongation
Ratio of un-recovered extension of the test specimen to its initial length after a
defined loading-unloading cycle, expressed as a percentage .
Let,
Q =Distance between applied reference marks after a specified recovery period
P =Initial distance between applied reference marks
Then,
Un-recovered elongation, C (%) =
Q−P
P
× 100
Recovered elongation
Recovered elongation is obtained by subtracting unrecovered elongation from 100%
Therefore,
Recovered elongation= (100 − C) Where, C is the un-recovered elongation
P
Q

Elastic recovery
Elastic recovery may be defined as the property of a body by which it tends to
recover its original size and shape from the deformation when the applied force is
removed.
Elastic recovery (%)=
Recovered strain
Total strain
× 100
=
CD
AB
BD
AB
× 100
=
CD
AB
× 100
BD
AB
× 100
× 100
=
recovered elongation
total elongation
× 100
=
CD
BD
× 100
=
recovered extension
total extension
× 100
Where,
AB= Original length
CD= Recovered extension
BD= Total extension
BC= Unrecovered extension
A B C D

Gauge Length
The gauge length is the original length of that portion of the specimen over
which the strain or change of length is determined
Stitch Length
Length of yarn contained in a knitted loop is called stitch length or loop
length. It includes the needle loop and half the sinker loop on either side of it .
Stitch length=
Course length
No of needles knitting
Course length
Course length refers to the measurement of a straight length of yarn knitted by
all or a fraction of the needles in the production of a particular course. It
consists of the stitch length multiplied by the number of needles knitting that
stitch length.
Course length= No. of needles knitting× Stitch length

Knit Stitch
When the needle is raised sufficiently high by the camming action
to obtain the yarn in the hooked portion of the needle and the old
loop is below the latch [i.e., the old loop is cleared], a knit stitch
will be formed as the needle descends.
Figure: Knit stitch (technical face) Figure: Knit stitch (technical back) Figure: Single jersey plain fabric

Tuck Stitch
A tuck stitch is composed of a held loop, one or more tuck loops and
knitted loops. It is produced when a needle holding its old loop also
receives the new loop, which becomes a tuck loop because it is not
intermeshed through the old loop but is tucked in behind it on the reverse
side of the stitch Tuck stitch structures show a faint diagonal line effect
on their surface.
Figure: Tuck stitch (technical face) Figure: Tuck stitch (technical back) Figure: Double lacoste fabric

Regression Analysis
It is a statistical tool used to determine the probable change in one variable
for the given amount of change in another. This means, the value of the
unknown variable can be estimated from the known value of another
variable.
The degree to which the variables are correlated to each other depends on
the regression line. The regression line is a single line that best fits the data,
i.e. all the points plotted are connected via a line in the manner that the
distance from the line to the points is the smallest. The regression also tells
about the relationship between the two or more variables .
Polyester Cotton (PC) blended yarn
Polyester cotton yarn, it is a blend of cotton and polyester. While cotton is a
completely natural fiber made from cotton plants, polyester is a manmade
fiber. PC yarn is a harmonious blend of both cotton and polyester in a way
that the advantages of both these fibers are brought into the resultant yarn .

• HATRA course length testerMachine name
• 50-1746/6
Model no
• England
Country of origin
• SDL International & Co. Ltd
Manufacturer
• To measure the course
length of sampleFunction
• 50-1000cmCourse length
range
Hatra course length tester
This equipment was used to determine the accurate
length of a complete course of knitted fabric
Machine specification:
Pulley
Supported
pin
Yarn
Dead weight
Measuring
scale
Figure : Hatra course length tester

• Constant Rate of
Extension(CRE)Measuring Principle
• 100N
Load Cell
• 100mm
Jaw Distance
• James H. Heal
Manufacturer
• England
Origin
• T17/T27
Jaw type
Figure 3.2: Titan Universal Strength
Tester
Titan Universal Strength Tester
This equipment was used to determine the elastic
recovery of different single jersey fabric.

Single
jersey
plain
2.60
mm
2.74
mm
2.88
mm
3.02
mm
3.16
mm
Fabric:
POLYESTER
COTTON
(30 Ne)
Polo
pique
2.60
mm
2.74
mm
2.88
mm
3.02
mm
3.16
mm
Double
lacoste
2.60
mm
2.74
mm
2.88
mm
3.02
mm
3.16
mm Single
lacoste
2.60
mm
2.74
mm
2.8
mm
3.02
mm
3.16
mm

Methodology
Rechecking of Stitch length values for the obtained samples
Standard : BS 5441:1988
Though the obtained samples were previously knitted at AUST laboratory, the stitch length values were
need to be verified for accuracy. The procedure for the above purpose is mentioned below.
o A full course was withdrawn from the fabric.
o After that one end of the course was attached with a pin of HATRA course length tester.
o After attaching an end of the yarn, the whole course was gradually straightened and laid around the
surface of the pulleys placed at the top and bottom. A dead weight was hanged at the other end of the
yarn.

Methodology
Rechecking of Stitch length values for the obtained samples
Standard : BS 5441:1988
o Then the reading was taken directly from the scale of the tester.
o The length of yarn, engaged in the pin surface, value of the course length of given
sample was measured.
o The whole procedure was repeated for 11 more times for each fabric to obtain
actual course length.
o At last by using that course length stitch length of each fabric was measured.

Methodology
Standard
BS EN 14704-1:2005
Preparation of test sample:
o The fabric samples were conditioned for 24 hours in a tension-
free state. Then the prepared specimens were conditioned in a
tension free state for a further 4hours after preparation to
minimize the effects of handling during preparation.
o Length wise test specimen were taken parallel to the wales and
width wise test specimen parallel to the courses.
o 300 mm×50mm test specimen were cut at both direction
(course wise & wale wise).
Figure : Gauge length
measurement by
calibrated rule
300
mm
50 mm

Methodology
Working Procedure:
o (100 ± 1) mm gauge length were set. The distance
was measured with the calibrated rule.
o Extension and retraction rate of the specimen were
set at 500 mm/min.
o The specimen was mounted centrally between the
two sets of line clamps at slack condition. Then the
machine was started for the test purpose.
100
mm
Figure : Line Contact jaw-
faces and specimen with
gauge marks

v
Methodology
Working Procedure:
o Different structure of single jersey fabric samples was tested in Titan Universal Strength
Tester to determine their elastic recovery at three different time intervals.
Figure : A screenshot from the TestWise™ Test Analysis Software
operating titan universal strength tester
Figure: Test specimen at
stretched condition
12345

DATA COLLECTION
Values of widthwise recovered elongation for change in stitch length for different types of single
jersey fabrics at different time period
Sample Stitch length (mm) Widthwise recovered elongation (%)
At 30 second At 1 minute At 30 minutes
Plain
2.60 72.6 73.6 78
2.74 71.4 72.6 75.4
2.88 61.8 62.8 67.8
3.02 56 57 63.6
3.16 52.2 53.8 57
Single
2.60 80.8 81.6 83.8
2.74 75.4 76.4 78.6
2.88 71.2 72.2 74.8
3.02 66.8 67.8 70.2

DATA COLLECTION
Values of widthwise recovered elongation for change in stitch length for different types of
single jersey fabrics at different time period
Sample Stitch length (mm) Widthwise recovered elongation (%)
At 30 second At 1 minute At 30 minutes
Double
Lacoste
2.60 84.2 85.4 86.8
2.74 82 82.8 85.2
2.88 77.8 78.8 81.4
3.02 74.2 75.2 77.4
3.16 70.4 71.6 73.8
Polo
Pique
2.60 76.8 77.6 80.8
2.74 72.4 73.6 76.2
2.88 68.8 69.8 72.4
3.02 65.4 66.4 68.8

Graphical analysis to show correlation between widthwise
recovered elongation and stitch length for different types
of single jersey structures

y = -40.143x + 178.41
R² = 0.9583
40
45
50
55
60
65
70
75
80
2.00 2.50 3.00 3.50
RECOVEREDELONGATION(%)
STITCH LENGTH (mm)
2.60 2.74 3.02 3.16
y = -39.429x + 177.51
R² = 0.9504
40
45
50
55
60
65
70
75
80
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
for plain fabric at 1 min
Linear (Stitch length vs
for plain fabric at 1
min)
y = -37.824x + 177.22
R² = 0.9797
40
45
50
55
60
65
70
75
80
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered
elongation for plain
fabric at 30 min
Linear (Stitch
length vs Recovered
elongation for plain
fabric at 30 min )
After30second
After1minute
After30minutes
Stitch length vs Recovered elongation for single jersey plain fabric

After30second
After1minute
After30minutes
y = -34.714x + 170.98
R² = 0.9961
40
45
50
55
60
65
70
75
80
85
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered
elongation for single
lacoste fabric at 30
sec
Linear (Stitch length
vs Recovered
elongation for single
lacoste fabric at 30
sec)
y = -34.429x + 171.11
R² = 0.9961
40
45
50
55
60
65
70
75
80
85
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered elogation
for single lacoste fabric
at 1 min
Recovered elogation
at 1 min)
y = -35.429x + 176.15
R² = 0.9886
40
45
50
55
60
65
70
75
80
85
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
at 30 min
at 30 min)
Stitch length vs Recovered elongation for single lacoste fabric

After30second
After1minute
After30minutes
y = -25.286x + 150.54
R² = 0.9923
40
45
50
55
60
65
70
75
80
85
90
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered
elongation for
double lacoste fabric
at 30 sec
vs Recovered
elongation for
double lacoste fabric
at 30 sec)
y = -25.143x + 151.17
R² = 0.9964
40
45
50
55
60
65
70
75
80
85
90
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered
elongation for double
lacoste fabric at 1
min
vs Recovered
elongation for double
lacoste fabric at 1
min)
y = -24.143x + 150.45
R² = 0.9831
40
45
50
55
60
65
70
75
80
85
90
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered
elongation for
double lacoste
fabric at 30 min
Linear (Stitch
length vs
Recovered
elongation for
double lacoste
fabric at 30 min)
Stitch length vs Recovered elongation for double lacoste fabric

After30second
After1minute
After30minutes
y = -30.714x + 156.9
R² = 0.9842
40
45
50
55
60
65
70
75
80
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered
elongation for polo
pique fabric at 30
sec
vs Recovered
elongation for polo
pique fabric at 30
sec)
y = -30.571x + 157.49
R² = 0.9838
40
45
50
55
60
65
70
75
80
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered
elongation for polo
pique fabric at 1 min
vs Recovered
elongation for polo
pique fabric at 1
min)
y = -31.857x + 163.83
R² = 0.9872
40
45
50
55
60
65
70
75
80
85
2.00 2.50 3.00 3.50
STITCH LENGTH (mm)
Stitch length vs
Recovered
elongation for polo
pique fabric at 30
min
Linear (Stitch
length vs
Recovered
elongation for polo
pique fabric at 30
min)
Stitch length vs Recovered elongation for polo pique fabric

Comment
o From the graphical analysis it is clear that stitch length is strongly correlated with
recovered elongation.
o Increase in stitch length results lower recovered elongation for different type of single
jersey fabric structures.
o Using the regression equation (as R2> 0.9) one may predict confidently the value of
recovered elongation from a particular stitch length. For example, a change of stitch length
by 0.01 mm may results a change in recovered elongation (after 30 minutes) of around
0.38% for plain jersey fabric, of around 0.35% for single lacoste fabric, of around 0.24%
for double Lacoste fabric and of around 0.32% for polo pique fabric respectively.

Graphical analysis to show correlation between widthwise
recovered elongation for different single knit structures at
different stitch length values

65
70
75
80
85
Double lacoste Single lacoste Polo Pique Plain
84.2
80.8
76.8
72.6
STRUCTURE
After30second
After1minute
After30minutes
65
70
75
80
85
90
85.4
81.6
77.6
73.6
STRUCTURE
70
75
80
85
90
86.8
83.8
80.8
78
STRUCTURE
Recovered elongation for experimental single jersey structures knitted at stitch length 2.60 mm

Recovered elongation for experimental single jersey structures knitted at stitch length 2.74 mmAfter30second
After1minute
After30minutes
65
70
75
80
85
82
75.4
72.4 71.4
STRUCTURE
65
70
75
80
85
82.8
76.4
73.6 72.6
STRUCTURE
70
75
80
85
90
85.2
78.6
76.2 75.4
STRUCTURE

After1minute
After30minutes
0
20
40
60
80
77.8
71.2 68.8
61.8
STRUCTURE
0
20
40
60
80
78.8
72.2 69.8
62.8
STRUCTURE
0
20
40
60
80
100
81.4
74.8 72.4 67.8
STRUCTURE

Recovered elongation for experimental single jersey structures knitted at stitch length 3.02 mm
After30second
After1minute
After30minutes
0
20
40
60
80
74.2
66.8 65.4
56
STRUCTURE
0
20
40
60
80
75.2
67.8 66.4
57
STRUCTURE
0
20
40
60
80
77.4
70.2 68.8
63.6
STRUCTURE

After1minute
After30minutes
0
20
40
60
80
70.4
60.8 58.8
52.2
STRUCTURE
0
20
40
60
80
71.6
61.8 59.8
53.8
STRUCTURE
0
20
40
60
80
73.8
63.2 62.2
57
STRUCTURE

Comment
o From the graphical analysis it is clear that structural construction of fabric influences the
recovered elongation.
o For the four experimental single knit structures, it was found that double lacoste showed
the highest elastic recovery where plain jersey showed the lowest.
o For example, the value of recovered elongation after 30 minutes is 73.8% for double
lacoste, 63.2% for single lacoste, 62.2% for polo pique and 57% for plain fabric at a loop
length value of 3.16 mm.
o It was also interesting to observe that most portion of elastic recovery occurred during the
first 30 sec i.e. at immediate removal of the external force.

Summarized graphical analysis for widthwise recovered elongation of different types of single
jersey structures with respect to stitch length
After30second
After1minute
After30minutes30
40
50
60
70
80
90
2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40
STITCH LENGTH (mm)
Plain Single Lacoste Double Lacoste Polo Pique
30
40
50
60
70
80
90
2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40
STITCH LENGTH (mm)
30
40
50
60
70
80
90
2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40
STITCH LENGTH (mm)

Discussion
o Stitch length has a direct influence on elastic recovery. Through the experimental
works it was found that elastic recovery decreases with the increase in stitch length.
As an example, a change of stitch length by 0.01 mm may results in a change of
elastic recovery for plain fabric by 0.40% after 30 second, by 0.39% after 1 minute,
and by 0.38% at 30 minutes respectively.
o Elastic recovery varies due to change in structural construction. Double Lacoste
fabric has the highest widthwise elastic recovery where plain jersey fabric has the
lowest, when other parameters remain constant. This type of change is mainly due
to the presence of tuck stitches in the fabrics structures. It may be also assumed that
the amount and positioning of tuck stitches in the structural repeat determined the
value of recovered elongation in different single knit structures.

Limitation
o The study was limited only to polyester-cotton blended knitted fabric due to
lack of other yarn / fabric types of similar quality.
o Standard atmosphere could not be maintained properly during the experimental
hours.

Conclusion
The research work was aimed to find out the influence of loop length, the most influential
knitting variable, on elastic recovery of weft knitted single jersey fabric. Also, the
constructional effects were examined of some extent here. It was found that a change in stitch
length by 0 .01 mm resulted less than 0.5% change in elastic recovery for different singe jersey
structures. On the other hand, all the experimental knit structures recovered more than 50% of
total elongation after a specified time period of 30 minutes. However, double lacoste showed
higher value of elastic recovery where single jersey plain fabric showed the lowest. Thus, a
manufacturer or customer may choose a single knit fabric from these categories considering the
required level of elastic property. A good scope still exists for double knit fabrics as well as
knitted fabrics of finished state for evaluation of their elastic recoveries.

stretch recovery of knitted fabric

stretch recovery of knitted fabric

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