56
CHAPTER 3
3
MATERIALS AND METHODS
The present study focusses on the tensile, flexural and
compressive properties of plain woven and twill woven of jute, sisal and
jute/glass hybrid structures. The effects of yarn linear density, weave types
(plain, twill), reinforcement fabric areal density and laying angle on
mechanical properties of such composites have also been investigated. Details
of the materials used and the various testing procedures employed are
presented in this chapter.
3.1
MATERIALS
Sisal, jute and glass yarns used in this study were purchased from
M/s GVR Enterprises, Madurai, India. The woven fabric was made through
customized plain loom by the researcher (Table 3.1). The yarn tensile data are
listed in Table 3.2
Table 3.1
Plain Loom details
Parameter
Details
Driving System By
Push Button Control On Both Side of Loom
Running Speed
160-180 RPM
Reed Space
200, 230, 250, 260, 280 cm
57
Weft Detection
By Piezo Electronic Slide Sensor
Cloth Roll dia.
400 mm
Driving Motor
1.5 kW, 960 RPM
Table 3.2
Tensile Properties of Yarns
Average Tenacity
Modulus
(cN/tex)
(cN/tex)
Jute
23
561.67
236
Sisal
32
723.5
198
Glass
57
1021
185
Type of Yarn
3.1.1
Twist per inch
Epoxy Resin
The generic term epoxy resin falls under the class of
thermosetting resins prepared by the ring-opening polymerization of
compounds containing an average of more than one epoxy group per
molecule. Epoxy resins traditionally made by reacting epichlorohydrin with
bis-phenol A, which are linear polymers that cross-link, forming thermosetting
resins basically by the reaction with the hardeners. The curing agent for the
epoxy resins usually is an amine. No volatile by-products are generated during
the curing process. During curing, epoxy resins can undergo three basic
reactions:
1.
Epoxy groups are rearranged and form direct linkages between
themselves.
2.
Aromatic and aliphatic hydroxyls link up to the epoxy groups.
3.
Cross-linking takes place with the curing agent through various
radical groups.
58
The advantages of epoxy resins are low polymerization
shrinkages, high mechanical strength, good electrical properties and chemical
resistance. The epoxy molecule also contains two ring groups at its centre
which are able to absorb both mechanical and thermal stresses better than
linear groups and therefore give the epoxy resin very good stiffness, toughness
and heat resistance. The primary disadvantage of epoxy resins is that it
requires long curing time. The epoxy resins are characterized by their high
adhesive strengths. This property is attributed to the polarity of aliphatic
hydroxyl groups and ether groups that exist in both the initial resin and the
cured system. This epoxy resin was purchased at M/s GVR Enterprises,
Madurai, India
3.2
METHODS -WEAVING OF JUTE AND SISAL YARN
Two kinds of weaving structures such as plain weave and twill
weave were developed to understand the influence of the weave on mechanical
properties of the composites. In a plain weave structure, each weft yarn passes
alternatively over and under one warp yarn, whereas in twill structures, each
weft or filling yarn floats across the warp yarns in a progression of interlacings
to the right or left, forming a pattern of distinct diagonal lines. Plain woven
and twill woven preforms were manufactured on a plain loom using 200,295
and 560 Tex jute yarn and 200,295 and 560 Tex sisal yarn in both warp and
weft direction. The fabric was 3.9 mm- 4.5mm thickness with (27/22/16
threads/inch) with an areal density of (240/300/388) g/m2
for
jute and
(280/330/405)g/m2. for sisal. The warp and weft crimp were calculated and
found to be 9.67% and 1.2% respectively. The samples were then used as such
for composite preparation.
59
3.3
COMPOSITE PREPARATION
The composite laminates were fabricated through hand lay-up
method. The preform fabrics were cut to 250mmx150mm size and layers
stacked in three different angles(0/0/0,0/45/0,0/90/0).The fibre volume
fraction were maintained between the ranges of 50-65% which were evaluated
using constituent densities. The amount of resin used to impregnate the
reinforcement was adjusted until to obtain a complete impregnation.
Laminates were cured in a hot-platen press for 2 hours at 50ºc with a pressure
of 3 bar, the composite laminates were post cured in an oven at 120ºc for one
hour.
Figure 3.1
3.4
Moulding Bath
YARN LINEAR DENSITY
Jute/Sisal yarn specimens were conditioned at 65±2% R. H. and
21±2ºC. The yarn linear density was characterized according to ASTM
D1059- 97. The conditioned yarn is cut in 1 meter lengths and weighed
through electronic balance. Ten specimens were measured and the average
weight (W) in grams was used for calculating the yarn linear density, where
60
(L) is the length of the yarn in meters, (K) is a constant, which equals 9000m/g
for denier and 1000m/g for tex.
Yarn linear density = (W x K) ∕ L
3.5
YARN STRENGTH
Jute and Sisal yarn specimens were tested for tensile strength
through Instron universal testing machine, model 3369 as per ASTM D 225602. Tests were performed using a gauge length of 50 mm and a strain rate of 2
mm/min. for ten specimens to obtain the yarn tensile properties.
3.6
FABRIC THICKNESS
Plain woven flax preform fabric thickness was measured
according to ASTM D 1777-96. A compress meter with a circular presser foot
of 9.53 mm in diameter was used for measuring the thickness. A pressure of
25KPa applied on the fabric to obtain the fabric thickness. Five randomly
selected locations were used to obtain the average value.
3.7
FABRIC WEIGHT PER UNIT AREA
A circular template was used to find out the fabric GSM.
Conditioned test specimens - using a circular template - were cut off from five
randomly selected locations and weighed using an electronic balance.
3.8
FABRIC TENSILE PROPERTIES
Plain woven Jute/Sisal fabrics tensile testing was carried out
using an Instron universal tester - model 3369. Twenty 30 mm wide test strips
61
were cut in the warp and weft directions. Then the yarns were removed from
test strips both sides until the specimen width was reduced to 25 mm. The
same procedure was followed for test strips in both warp and weft directions.
Tensile tests were performed using a gauge length of 50 mm and a strain rate
of 2 mm/min.
3.8.1
Tensile Strength of Composites
Tensile strength is the maximum stress at the breaking point of
composite specimen. Tensile tests were conducted as per ASTM-D 638
through Instron testing machine of Model 3369 at 2 mm/min rate of loading.
Test specimens were cut from the laminates along the longitudinal axis and in
the width wise direction. The specimen was placed in the grips of the testing
machine and the grips were tightened evenly. Five specimens were tested for
each sample. Tensile strength and tensile modulus were calculated using the
following relations in both warp and weft directions.
Tensile Strength 
P
bd
Tensile Modulus 
P  l 
l  bd 
(3.1)
(3.2)
Where P = load in N, l is gauge length in mm, b = width in mm and
d = thickness in mm.
3.8.2
Flexural Strength of Composites
It is the maximum stress developed on the composite when the
test specimen acting as a simple beam, is subjected to a bending force
perpendicular to the bar. The flexural tests were conducted as per ASTM
D790, on a Kalpak universal testing machine at 5 mm/min rate of loading.
62
Test specimens were cut from the laminates along the longitudinal axis and in
the width wise direction. Specimens were loaded in three-point bending.
Flexural stress is given by
3PL
f  2bd
2
(3.3)
Where, P is the maximum load at failure (N), L the support span(mm), and b
and d are the width and thickness of the specimen (mm) respectively.
The flexural modulus is calculated from the slope of the initial
portion of the load-deflection curve. Flexural modulus is given by
E
L3m
4bd3
(3.4)
Where, m is the initial slope of the load-deflection curve. In each lay-up angle
and laminate thickness of 2 and 4 mm, five specimens were tested and the
average result is used.
3.8.3
Compressive Strength of Composites
This method determines in-plane compressive properties by
applying the compressive force into the specimen at wedge grip interfaces.
ASTM D3410 is most appropriate for composites materials Reinforcement by
high-modulus fibers including tape and textile, but other materials may be
tested. The test fixture is designed to provide a compressive load to the
unsupported center 12 to 25 mm (0.5 to 1 inch) gauge length of the specimen.
Test Procedure:
A fixture is used to align the specimen in the wedge grips and the
grips are therefore tightened. The wedges are inserted into the compression
63
fixture, and if an extensometer is being used to measure strain, it is attached to
the specimen. The specimen is compressed to failure.
3.9
TAGUCHI METHOD OF OPTIMIZATION
Taguchi method is considered as one of the most comprehensive
approach in product/process developments. The same was carried out by
Taguchi methodology using Design Expert-7 Software. The main objective of
this method is to optimize the process variables which influences the process
outcome. Since three controllable factors and three levels of each factor are
considered, L9 (3X3) Orthogonal Array was selected for this study.
Taguchi method is a statistical method developed by Dr. Genechi
Taguchi and Konishi. They proposed many theories on optimization of process
variables. The method involves identification of proper control parameters to
obtain the optimum results of the process. The process optimization should be
carried out in three-step approach- system design, parameter design, and
tolerance design. System design deals with innovative research, and it concern
about the selection of controllable factors. Parameter design is meant for
arraiving the optimum levels of process parameters to improve the
performance of process through adjusting levels of factors. The tolerance
design aims at determining the control characteristics for each factor level
(Martin et al.,2008). The parameter design is the important step in Taguchi
method to achieve high quality without increasing in cost.
The following steps are involved to execute the Taguchi parameter design
such as,
(i)
Identify the objective function to be optimised
(ii)
Identify the control factors and their levels
(iii)
Select a suitable orthogonal Array and construct a matrix.
(iv)
Conduct the matrix experiment
64
(v)
Examine the data, predict the optimum control factor levels and
its performance
(vi)
Conduct the verification Experiment with selected optimum
variables for validation.
To select an appropriate orthogonal array for experiments, the
total degrees of freedom need to be computed. The degrees of freedom are
defined as the number of comparisons between process parameters that need to
be made to determine which level is better and specifically how much better it
is. The degrees of freedom for the orthogonal array should be greater than or
equal to those for the selected process parameters. For three parameters each at
three levels, the degrees of freedom are six and then select an appropriate
orthogonal array to fit the specific task (Nassir S et al., 2011). A three level
orthogonal array (L9 3X3) with nine experimental runs (total degrees of
freedom = 9-1 = 8) were executed for the present study. The orthogonal array
(OA) which is one of the simplest method which provides the possibility to
change all combination of parameters at the same time and their effect and
performance interactions are studied simultaneously (Randhir Kumar et al.,
2012).
The application of Taguchi method, based on orthogonal array,
reduces the numbers of experiments with respect to full factorial design. This
method predicts the quality characteristics by finding the S/N ratio for
engineering design problems. The performance criteria for optimization of the
response parameter of S/N ratio are in three categories such as lower-thebetter, larger-the-better, and nominal-the-best. Keeping the variance in the
output as minimum is the main objective of this method . Taguchi‘s
optimization procedure is adopted in the field of engineering applications
rather than advanced statistical techniques. In Orthogonal array, the columns
are mutually orthogonal which means in any pair of columns, all combination
of factor levels occurs. A typical example for orthogonal matrix design is ―L9‖
65
design, here 9 representing 9 rows of experiments to be tested, another
parameter in this design is S/N ratio, which is expressed in decibels (dB).It is
also represented as sensitivity to variability. This design is used to study the
entire parameter space with lesser number of experiments to be excuted. The
higher the S/N ratio, the better the product quality. Once the S/N value
becomes maximum, the noise factor minimizes, which really makes a
significant impact on process performance.
The method of analysing the performance characteristics of S/N
ratio depends upon the three categories as smaller- the-better(or) Lower-the better, larger- the- better(or) higher-the-better and nominal- the- best
When Lower is better
n


S / N   10 * log 1 / n  Yi2 
i 1


(3.5)
When higher is better
n

1 
S / N   10 * log 1 / n  2 
i 1 Yi 

(3.6)
When n is the number of experiments in the orthogonal array and yi the ith
value measured.
When Nominal is the best
 Y2 
S / N   10 * log  2 
 
Where y2 is the average data and
(3.7)
 2 the variation.
In this research work, the criteria for optimization of the response
parameters was based on the larger the better S/N ratio. The effect of three
preform parameters such as yarn linear density, fabric areal density and laying
angle on mechanical properties (Tensile, flexural and compression) of the
composites were analysed in this research work using Taguchi‘s orthogonal
matrix. The factors that are influencing the above mechanical properties of the
66
resultant composites were analyzed through cause and effect diagram and then
experiments have been carried out by trial and error closeted range of the
values in the selected process parameters.
Figure 3.2
Cause and Effect Diagram
The cause and the revealed factors were expected to have an
effect on the strength of the resultant composite materials. Since the composite
manufacturing process follows the hand layup method, process parameter
cannot influence significantly and due to cost constrain, this study is done
through a single matrix material such as Epoxy resin. Moreover this study
focused on bringing new form reinforcement such as woven Sisal, Woven jute
and hybrid woven structures. In this research work, the researcher considered
the reinforcement parameter as experiment parameter such as type of weave,
yarn linear density, fabric GSM and fabric laying angle.
67
Table 3.3
Composite set-1
Various Composite Combinations
Composite set-2
Composite set-3
Jute
Sisal
Hybrid(Jute/Glass)
Yarn linear density
Yarn linear density
Yarn linear density
Fabric Areal Density
Fabric Areal Density
Fabric Areal Density
Laying Angle
Laying Angle
Laying Angle
As per the Table 3.3, the composite constructions have been
made. In each composite set, eighteen experiments were carried out and then
the optimization processes were executed through Taguchi‘s method.