ABSTRACT

Presented in this report is a study to develop a system

which provides information about damages and deformation of an

onboard aircraft using compression load cell sensor array

embedded in glass fiber reinforced polymer (GFRP) based

composite materials. Interest in, and utilization of, FRPs in

engineering products has steadily grown over the last three

decades. Their high strength-to-weight ratios and rot and

corrosion resistances are advantages for an increasing number

of diverse applications from armory through to yachting and

land transportation.

Composite materials have been increasingly used in

automotive engineering, aerospace development, marine

technology, electronic devices, and construction industries.

General purposed commercial finite element code was employed

to develop the computational model. Glass fiber reinforced

composite, one of the commonly used structural composites, was

chosen for the test material. Computational model was

constructed using 3- D finite elements. For comparison

purpose, compression load test was carried out the load and

the specimen size as close as possible to those used in

computational model. Both computational and experimental

results are found to be in good agreement in terms of damage

size.

1

A simple setup to predetermine the fracture load is

fabricated and a test for load condition of 4kgs. is chosen to

test the setup and a successful attempt is made to show the

capabilities of the setup.

CONTENTS

CHAPTER TITLEPAGE

NO

1INTRODUCTION 51.1 Process of Manufacturing of

Composite Materials

5

1.2 Computational Methods 6

2

LITERATURE SURVEY 92.1 COMPOSITE MATERIAL 92.2 The Method of Producing Fiber Glass

Reinforced Polymer

9

2

2.2.1 Open Molding 10

2.2.2 Vacuum Bag Molding 10

2.2.3 Pressure Bag Molding 10

2.2.4 Autoclave Molding 11

2.2.5 Resin Transfer Molding (RTM) 11

2.2.6 The Definition of Glass Fiber 12

2.2.7 Properties of Glass Fiber

composites

12

2.2.8 Glass Reinforced Plastic (GRP) 13

2.2.9 Applications of Glass Polymer 14

2.2.10 Factors Affecting The Fatigue

Life Of GFRP

15

2.2.11 Static Compression Failure

Mechanisms

16

2.2.12 Fatigue Damage Mechanics 22

3

METHODOLOGY AND MODELLING 223.1 Experimental Analysis 24

3.2 Numerical Analysis 24

3.3 Modelling 26

3.4 Preprocessing 27

3.5 Setup 293

3.6 Postprocessing 31

4

Setup for Predetermination of Fatigue

And Fracture In Glass Fiber Reinforced

Composite Laminate

33

4.1 Block Diagram 33

4.2 Load Cell Working 33

4.3 Softwares Used 34

4.4 Hardware Description 344.5 Load cell 344.6 Characteristics of Load Cell 35

4.7 Pic Micro Controller 35

4.8 Features of PIC16f877 36

4.9 General Features 36

4.10 Key Features 36

4.11 Analog Features 37

4.12 Special Features 37

4.13 PIN Diagram 38

4.14 Input/output Ports 38

4.15 LCD Display 40

4.16 Power Supply Circuit Diagram 40

4

4.17 Buzzer and Led Indicators 414.18 Setup for Predetermination of

Fatigue and Fracture in Glass Fiber

Reinforced Composite Laminate

42

5 RESULTS AND DISCUSSIONS 456 REFERENCES 46

5

1.INTRODUCTION

Composite materials (or composites for short) can be defined

as engineered materials made from two or more constituent

materials which contain significantly different physical or

chemical properties and remain separate and distinct on a

macroscopic level within the finished structure. There are two

types of composite, the first one is short fiber reinforced

polymer and the other one is continuous fiber reinforced

polymer.

Glass fiber reinforced polymer or plastic is one of the

example of composite material. Fiberglass is material made

from extremely fine fibers of glass. The role of these fibers

is as a reinforcement agent for polymer products. Fiber glass

is widely used in electronic, marine and automotive

industries.

With the increased application of glass fiber composite in

dynamic situation, knowledge of impact strength of this

material is becoming important. As such, considerable amount

of research has devoted to study the strength of this

6

composite under dynamic load using computational and

experimental methods.

1.1 Process of Manufacturing of Composite Materials

Composite materials can be produced by a range of

processes. These vary from the manual lay-up of reinforcement

and hand application of resin to fully automated continuous

processes. The most common techniques are:

Hand or spray lamination is the most common process,

accounting for over 40% of composite production

worldwide. This is due to its flexibility, which allows

use of all reinforcement types. The use of polyester

resins dominates, but epoxy and vinyl ester resins are

also used.

Compression molding accounts for about 25% of all

composites processing worldwide. It is a highly automated

process in which pressure is used to force preheated

resin to adopt the shape of the mold and impregnate the

reinforcement. The process uses thermosetting resins and

heat and pressure are applied until the resin is cured.

Resin injection production accounts for about 5% of

global FRP composite production. It can be a highly

automated technique, producing smooth-sided parts and

delivering low volatile organic chemical emissions.

Pultrusion is a highly automated process suited to the

production of continuous profiles such as I beams, T

7

sections and tubing. Continuous fibers are impregnated

with resin, then pulled through a shaping die and cured.

Pultrusion processes are used to produce about 5% of

global FRP composites.

Vacuum infusion reduces emissions, compared to hand

lamination, by employing a fully enclosed mold.

Components can be exactly reproduced offering higher

quality and performance.

Prepregs, i.e. reinforcement material pre-impregnated

with resin, is supplied as a sheet ready for use by the

molder. Most are based on epoxy resin and carbon fiber.

Continuous sheet production produces flat or corrugated

translucent or colored profile. A layer of resin is

deposited onto moving polymer film. Chopped glass fiber

is then added and impregnated with resin. The resin is

then cured.

1.2 Computational Methods

Among the computational method, finite element method (FEM)

is a widely used method due to its flexibility to model and

analyze variety of engineering problems. Some popular FE

packages p to date are Algor Software, ANSYS, Dyna and many

more.

Major advantage of FEM is we can reduce the cost of

experimenting. Impact analysis is expensive whereas the

material will be analyzed and it will be failed intentionally.

8

Another than that, the analysis is a time consuming process,

by using FEA method we can save a lot of valuable time and

reduced losses.

Based on the information and published journal found, the

number of journal that related to the compression load test of

fiber glass is still low. The journals found are mostly

research on other composite materials such as carbon fiber and

so on. With this compression load test, it will give other

researchers the new information on fiber glass characteristic.

Of the different fiber types the most economic, and

therefore most commonly used, fibers are made from glass.

Depending on the application this glass may be low alkali

content “E-glass” or alkali resistant “AR-glass” for use in

reinforcing bar for concrete. High strength glass fibers are

available and are used in aerospace applications. Carbon

fibers, well known from the aircraft and high performance car

applications that have used them for many years, offer

superior rigidity compared to glass fibers. However, this

additional performance commands a higher price. Aramid fibers

can be either low modulus, e.g. for energy absorption in body

armor, or high modulus for aerospace applications.

The structure of the reinforcement can also be varied

depending on application and manufacturing method. Use of

chopped glass fibers and chopped stand mats both result in

randomly orientated fibers in the final product. This format

9

is cheap, easy to use and is used in large quantities for

reinforcement of deck coverings and in translucent corrugated

roofing profiles. There it enhances puncture and movement

resistance. Woven glass roving offer greater direction

strength and can be used to increase unidirectional or bi-

directional strength. Thin glass surface tissue, or scrim, can

be used when a resin-rich surface is needed. Continuous

fibers, oriented in a single direction, offer the ultimate

properties along the axis of the fibers, but the cross-

direction of the product inevitably has lower properties.

Careful design of the part is, therefore, essential to make

best use of this anisotropy.

Matrix resins can be selected from a number of different

chemistries. The choice is generally based upon the required

performance and, of course, cost. Polyethylene and

polypropylene are the cheapest thermoplastic resins. These

materials typically find applications in composite cable

applications where lightweight and reasonable environmental

resistance are attractive attributes. Polyester thermosetting

resin materials are also a cost conscious choice. They offer

moderate environmental resistance and have been widely used in

New Zealand for the production of FRP roof profiles. Epoxy

resins are also thermosetting, but cost about twice as much as

polyester resins. They are perceived to offer superior

environmental resistance.

10

Polyurethane thermoplastic resins offer even better

environmental resistance, but also cost about twice as much as

polyester-based composites. They find applications in

aggressive environments, such as chemical plants, where they

are used to substitute for metals. Phenolic-based thermoset

systems have cornered the off-shore platform market. Good

resistance to fire and the highly saline environment have

driven this trend. Phenolic materials are also cost

competitive with polyester materials, which implies that they

have potential for wider use in construction.

The project has focused in the areas of glass fiber

composite reinforced materials under compression load. The

glass fiber is fabricated and subjected to a periodically

sampled dynamic stress and the structural health is monitored,

thus detecting the failure earlier. A compression load sensor

is used to measure the change in strain or force by converting

them to an electrical charge. A compression load sensor use

property that by occurring any vibrations or movement of

particles of materials within it generate an electric current.

11

.

2. LITERATURE SURVEY

The main purpose if this literature review is to get

information about the project reference books, magazines,

journals, technical papers and web sites. In this chapter, the

information gathered from a variety of sources will be

discussed.

2.1 Composite Material

Composite materials or composites for short are engineered

materials made from two or more constituent materials. Each

one of them has significantly different physical or chemical

properties. The combination of the materials can remain

separate and distinct on a macroscopic level within the

finished structure. These materials are widely used in

automotive industries, boat making industries and so on.

2.2 The Method of Producing Fiber Glass Reinforced Polymer

Generally, the reinforcing and matrix materials are

combined, compacted and processed to undergo a melding or a

blending event. After the melding event, the part shape is

essentially set, although it can deform under certain process

conditions.

12

For a thermo set polymeric matrix material, the melding

event is a curing reaction that is initiated by the

application of additional heat or chemical reactivity such as

organic peroxide. For a thermoplastic polymeric matrix

material, the melding event is solidification from the melted

state. For a metal matrix material such as titanium foil, the

melding event is a fusing at high pressure and a temperature

near the melt point. In process of producing fiber glass

reinforced polymer, there is several most popular method used

in the industries.

2.2.1 Open Molding

Open molding is a process using a rigid, one sided which

shapes only one surface of the panel. While the opposite

surface is determined by the amount of material placed upon

the lower mold. Reinforcement materials can be placed manually

by human or robotically. For the examples of reinforcement

agent are continuous fiber forms fashioned into textile

constructions and chopped fiber. The matrix is generally a

resin, and can be applied with a pressure roller, a spray

device or manually. This process is generally done at ambient

temperature and atmospheric pressure. Two variations of open

molding are Hand Lay-up and Spray-up.

2.2.2 Vacuum Bag Molding

This process using a two-sided mold set that shapes both

surfaces of the panel. On the lower side is a rigid mold and

13

on the upper side is a flexible membrane or vacuum bag. The

flexible membrane can be a reusable silicone material or an

extruded polymer film. Then, vacuum is applied to the mold

cavity. This process can be performed at either ambient or

elevated temperature with ambient atmospheric pressure acting

upon the vacuum bag. Most economical way is using a venturi

vacuum and air compressor or a vacuum pump.

2.2.3 Pressure Bag Molding

This process is related to vacuum bag molding in exactly the

same way as it sounds. A solid female mold is used along with

a flexible male mold. The reinforcement is place inside the

female mold with just enough resin to allow the fabric to

stick in place. A measured amount of resin is then liberally

brushed indiscriminately into the mold and the mold is then

clamped to a machine that contains the male flexible mold.

The flexible male membrane is then inflated with heated

compressed air or possibly steam. The female mold can also be

heated. Excess resin is forced out along with trapped air.

Cycle times for a helmet bag molding machine vary from 20 to

45 minutes, but the finished shells require no further curing

if the molds are heated.

2.2.4 Autoclave Molding

A process using a two-sided mold set that forms both

surfaces of the panel. On the lower side is a rigid mold and

14

on the upper side is a flexible membrane made from silicone or

an extruded polymer film such as nylon. Reinforcement

materials can be placed manually or robotically. They include

continuous fiber forms fashioned into textile constructions.

Most often, they are pre-impregnated with the resin in the

form of prepreg fabrics or unidirectional tapes. In some

instances, a resin film is placed upon the lower mold and dry

reinforcement is placed above. The upper mold is installed and

vacuum is applied to the mold cavity. The assembly is placed

into an autoclave pressure vessel. This process is generally

performed at both elevated pressure and elevated temperature.

The use of elevated pressure facilitates a high fiber volume

fraction and low void content for maximum structural

efficiency.

2.2.5 Resin Transfer Molding (RTM)

A process using a two-sided mold set that forms both

surfaces of the panel. The lower side is a rigid mold. The

upper side can be a rigid or flexible mold. Flexible molds can

be made from composite materials, silicone or extruded polymer

films such as nylon. The two sides fit together to produce a

mold cavity. The distinguishing feature of resin transfer

molding is that the reinforcement materials are placed into

this cavity and the mold set is closed prior to the

introduction of matrix material.

15

Resin transfer molding includes numerous varieties which

differ in the mechanics of how the resin is introduced to the

reinforcement in the mold cavity. These variations include

everything from vacuum infusion (see also resin infusion) to

vacuum assisted resin transfer molding. This process can be

performed at either ambient or elevated temperature.

2.2.6 The Definition of Glass Fiber

Fiberglass also called fiberglass and glass fiber is

material made from extremely fine fibers of glass. It is used

as a reinforcing agent for many polymer products. The

resulting composite material, properly known as fiber-

reinforced polymer (FRP) or glass-reinforced plastic (GRP), is

called "fiberglass" in popular usage in the industries.

Glassmakers throughout history have experimented with glass

fibers, but mass manufacture of fiberglass was only made

possible with the advent of finer machine-tooling. In 1893,

Edward Drummond Libbey exhibited a dress at the World's

Columbian Exposition incorporating glass fibers with the

diameter and texture of silk fibers. What is commonly known as

"fiberglass" today, however, was invented in 1938 by Russell

Games Slayter of Owens-Corning as a material to be used as

insulation. It is marketed under the trade name Fiberglass,

which has become a generalized trademark.

2.2.7 Properties of Glass Fiber composites

16

Glass fibers are useful because of their high ratio of

surface area to weight. However, the increased surface area

makes them much more susceptible to chemical attack. By

trapping air within them, blocks of glass fiber make good

thermal insulation, with a thermal conductivity of 0.05 W/m-K.

Glass strengths are usually tested and reported for "virgin"

fibers: those which have just been manufactured. The freshest,

thinnest fibers are the strongest because the thinner fibers

are more ductile. The more the surface is scratched, the less

the resulting tenacity. Because glass has an amorphous

structure, its properties are the same along the fiber and

across the fiber. Humidity is an important factor in the

tensile strength. Moisture is easily adsorbed, and can worsen

microscopic cracks and surface defects, and lessen tenacity.

In contrast to carbon fiber, glass can undergo more

elongation before it breaks. The viscosity of the molten glass

is very important for manufacturing success. During drawing

(pulling of the glass to reduce fiber circumference) the

viscosity should be relatively low. If it is too high the

fiber will break during drawing, however if it is too low the

glass will form droplets rather than drawing out into fiber.

2.2.8 Glass Reinforced Plastic (GRP)

Glass-reinforced plastic (GRP) is a composite material or

fiber-reinforced plastic made of a plastic reinforced by fine

fibers made of glass. For the example of graphite-reinforced

17

plastic, the composite material is commonly referred to by the

name of its reinforcing fibers (fiberglass). The plastic is

thermosetting, most often polyester or vinylester, but other

plastics, like epoxy (GRE), are also used. The glass is mostly

in the form of chopped strand mat (CSM), but woven fabrics are

also used.

As with many other composite materials (such as

reinforced concrete), the two materials act together, each

overcoming the deficits of the other. Whereas the plastic

resins are strong in compressive loading and relatively weak

in tensile strength, the glass fibers are very strong in

tension but have no strength against compression. By combining

the two materials together, GRP becomes a material that

resists well both compressive and tensile forces. The two

materials may be used uniformly or the glass may be

specifically placed in those portions of the structure that

will experience tensile loads.

2.2.9 Applications of Glass Polymer

GRP was developed in the UK during the Second World War

as a replacement for the molded plywood used in aircraft

radomes (GRP being transparent to microwaves). Its first main

civilian application was for building of boats, where it

gained acceptance in the 1950s. Its use has broadened to the

automotive and sport equipment sectors, although its use there

is being taken over by carbon fiber which weighs less per

18

given volume and is stronger both by volume and by weight. GRP

uses also include hot tubs, pipes for drinking water and

sewers.

Advanced manufacturing techniques such as pre-pregs and

fiber rovings extend the applications and the tensile strength

possible with fiber-reinforced plastics.

GRP is also used in the telecommunications industry for

shrouding the visual appearance of antennas, due to its RF

permeability and low signal attenuation properties. It may

also be used to shroud the visual appearance of other

equipment where no signal permeability is required, such as

equipment cabinets and steel support structures, due to the

ease with which it can be molded, manufactured and painted to

custom designs, to blend in with existing structures or

brickwork. Other uses include sheet form made electrical

insulators and other structural components commonly found in

the power industries.

Glass reinforced plastics are also used in the house

building market for the production of roofing laminate, door

surrounds, over-door canopies, window canopies & dormers,

chimneys, coping systems, heads with keystones and cells. The

use of GRP for these applications provides for a much faster

installation and due to the reduced weight manual handling

issues are reduced. With the advent of high volume

manufacturing processes it is possible to construct GRP brick

19

effect panels which can be used in the construction of

composite housing.

These panels can be constructed with the appropriate

insulation which reduces heat loss. The fiber glasses are also

widely used in piping such as underground as well as above.

For example, the firewater systems, cooling water systems,

drinking water systems and waste water systems or sewage

systems.

In polymer composites, the matrix is the major load bearing

component. In order to increase this load bearing capability,

the reinforcements are introduced into the matrix.

Almost all engineering components are subjected to varying

loads throughout their working life, and fatigue is easily the

most common failure in service. Fatigue in materials is their

response to cyclic loading or, in other words, fatigue is a

process whereby mechanical damage caused by repetitive or

fluctuating stresses results in a material failure at lower

stress levels than would be required under static loading. The

purpose of this review is to understand the fatigue life

diagrams, damage mechanisms and various factors, which

influence the fatigue properties of Glass Fiber Reinforced

Plastics (GFRP). This is followed by review of literature on

the effect of fiber prestress on the fatigue performance of

composites.

2.2.10 Factors affecting the fatigue life of GFRP

20

Fatigue life can be influenced by frequency, stress

concentration, stress levels, temperature and environment.

(i) Frequency and temperature the monotonic strengths of

GFRP are markedly loading-rate dependent, by virtue of the

viscoelastic character of the matrix and because the strength

of the glass fibers is rate dependent, the fatigue response

will vary with test frequency. Unlike CFRP, GFRP composites

cannot readily dissipate heat and they gradually heat up

during cycling. The structure and properties of glass

reinforcement will not be influenced by this temperature

difference, but the matrix properties can be substantially

altered. Mainly the residual stress state will be altered due

to the superposition of thermally-induced stresses, which in

turn will reduce the strength properties of the matrix. The

matrix strength decrease will adversely affect the transverse

strength of unidirectional plies so that the cross-ply will

begin to fail. Thus, fatigue failure is hastened. Generally

laminates dominated by mainly continuous fibers in the test

direction show lower strains and little hysteresis heating at

test frequencies around 10 Hz.

(ii) Stress Levels the mean tensile stress has been shown

to have an important effect on the fatigue properties of fiber

reinforced composites. For 0° and ±15° E-glass/epoxy

laminates, the stress amplitude at a constant life tends to

decrease with increasing tensile mean stress. In GFRP there is

a significant rate effect; the greater the rate of testing the21

greater the strength. Therefore, in GFRP static and fatigue

tests are carried out at the same rate.

(iii) Environment In GFRP, the moisture content has a

detrimental effect mainly due to the stress corrosion of

fibers. In matrix resins, the moisture may act as a

plasticizer and will lead to higher failure strains. This may

tend to increase fatigue resistance by inhibiting local crack

growth. However, water also weakens the reinforcing glass

fibers so that the net result is more likely to be a reduction

in fatigue resistance. The water ingress may be stopped by

efficient fiber matrix adhesion and by minimizing debonding.

2.2.11 Static Compression Failure Mechanisms

The compressive strength of unidirectional fiber reinforced

composites is typically 60 – 80 % of their tensile strength as

a consequence of 0° fiber micro buckling, 98, and 99 which is

of major concern since there are many applications in which

such materials are subjected to high compressive stress. An

understanding of the phenomena involved in compressive failure

is crucial to the development of improved composite materials.

Modes of failure Jelf and Fleck100 identified elastic micro

buckling, fiber crushing, matrix failure and plastic micro

buckling as failure from experiments on model composite

systems designed to exhibit one particular mode.

22

Generally, three macroscopic failure modes are observed in

unidirectional composites. The first mode of failure is

associated with poor fiber-matrix adhesion, which will lead to

interfacial failure and longitudinal splitting. As most of the

engineering composite systems involve fairly strong

interfaces, this usually is not the dominant mode of failure.

The second mode of failure is associated with fiber micro

buckling and kink-band formation. A significant number of

previous experimental results have revealed that fiber micro

buckling and kink-band failure along the fiber direction of a

unidirectional composite are the initiating mechanisms of

compressive failure that lead to global instability. The third

mode of failure is fiber “crushing” which is associated with

pure compressive failure of the fibers themselves. This occurs

when the axial strain within the composite attains a value

equal to the critical crushing strain of the fibers. This

higher compressive strength failure mode is usually prevented

by the occurrence of fiber micro buckling at lower stress

levels due to fiber misalignment.

2.2.12 Fatigue Damage Mechanics

Fatigue damage can be defined as the cyclic-dependent

degradation of internal integrity. The degree of influence of

these changes in integrity on the mechanical response of

materials may vary greatly. This suggests that one will only

be concerned with those damages, which are directly related to

strength, stiffness, or service life of the component.23

Composite materials exhibit very complex failure mechanisms

under static and fatigue loading due to the anisotropic

characteristics of their strength and stiffness. They

accumulate damage in a random rather than a localized fashion,

and failure does not always occur by propagation of a single

macroscopic crack. The basic microstructural mechanisms of

damage accumulation in composites are fiber-matrix debonding,

matrix cracking, delamination and fiber breakage. Any

combination of these could cause fatigue damage that will

result in reduced strength and stiffness. Both the type and

degree of damage vary widely, depending on material

properties, laminations and type of fatigue loading. For any

composite, in the early stages of fatigue life, the weak

fibers will begin to break in a random fashion throughout the

loading region. Locally, the matrix will transfer the loads

shed by the broken fibers into neighboring fibers. At

reasonable working strains, an unbroken fiber reinforcement

network carries the majority of the load in the composite.

When the stress amplitude is above the elastic levels of the

matrix, viscoelastic flow occurs preferentially between

closely spaced fibers, because of the high strain

magnification in these regions. This flow will not be fully

reversible when the stress is reduced and during cyclic

loading additional stress and strain concentrations develop

which lead to the initiation of debonding at applied stresses

below those observed in monotonic loading. The debonding

cracks grow during cyclic loading because some flow occurs at24

the crack tip during the loading half of the cycle, which is

not fully reversed on unloading. As in uniaxial tensile tests

the cracks nucleate and propagate in regions of closely spaced

fibers by the growth and coalescence of individual fiber

debonds. When the fibers are widely spaced, the growth of the

crack from one fiber to the next depends on the fatigue crack

growth resistance of the matrix. As the laminate is further

stressed, matrix cracking will subsequently occur from the

weakest (transverse ply) to the strongest layers

(unidirectional ply). The majority of the fatigue life of a

laminate is spent in the crack multiplication stage where the

density of cracks increases.

Bledzki et al have investigated the effect of introduction

of Flax and jute fibers on the mechanical properties of the

composites. Increasing the fiber content results in an

increase in the shear modulus and impact strength of the

composites. Many similar studies on natural fibers such as

bamboo, flax, hemp and kenaf reveal that the mechanical

properties of Fiber reinforced composites depend on several

fiber parameters such as fiber length, fiber loading, fiber

aspect ratio, fiber orientation and fiber matrix adhesion.

The use of cellulosic fiber reinforced polymer composites is

beneficial as they are cheap, light weight, and pose no health

hazards to people working with them. This has a potential for

structural applications. But, despite these benefits, the

natural fiber polymer matrix composites have numerous25

disadvantages such as lower modulus, low strength and poor

moisture resistance. It has been seen from previous studies

that the moisture causes the degradation of natural fibers

faster than synthetic fibers, owing to their organic nature.

Thus the hybridization of natural fibers with synthetic

fibers, which are stronger and more corrosion resistant are

gaining much interest. The idea is that by using two types of

fibers in a hybrid composite, the shortcomings of one can be

compensated by the advantages of the other. Through proper

material design, a balance in properties may be achieved.

The degree of mechanical reinforcement that can be obtained

by the addition of Glass fibers in bio-fiber reinforced

polyester composites has been studied by Mishra et al. It was

found that the addition of relatively small amounts of glass

fiber to the polyester matrix based pineapple leaf fiber and

sisal fiber-reinforced enhanced the mechanical properties,

resulting in a positive hybrid effect. Optimum glass fiber

loadings for PALF/glass hybrid polyester and sisal/glass

hybrid polyester composites are 8.6 and5.7 wt. percentage

respectively. It has also been found that the degree of

moisture absorption of hybrid composites is less than that of

single fiber composites.

Jacob et al (2003) studied the effects of concentration

of fibers, fiber ratio and the modification of fiber surface

in sisal/oil palm hybrid fiber reinforced rubber composites.

Increasing the concentration of fibers resulted in reduction26

of tensile strength and tear strength. At the same time, an

increase in modulus of the composites was also seen. The

vulcanization parameters, processability characteristics, and

stress–strain properties of these composites were analyzed.

The rubber/fiber interface was improved by the addition of a

resorcinol-hexamethylene tetramine bonding system. It was

revealed from the fiber breakage analysis that the extent of

breaking was low. It was also found that the mechanical

properties of the composites in the longitudinal direction of

the fibers were superior to that in the transverse direction.

The mechanical properties of a composite laminate based

on natural flax fiber reinforced recycled high density

polyethylene under conditions of tensile and impact loading

were investigated by Singleton et al (2003). They determined

the stress–strain characteristics, of yield stress, tensile

strength, and tensile (Young’s) modulus, of ductility and

toughness as a function of fiber content experimentally. It

was seen that by changing the fiber loading and by controlling

the bonding between the layers of the composite, improvements

in strength and stiffness combined with high toughness can be

achieved. The mechanical properties were found to be optimum

for 15 – 20 % of flax fiber loading. It was also seen that

material properties show greater degree of variation at higher

fiber volume fractions, due to fiber clumping.

Velmurugan et al (2007) studied the mechanical properties

of randomly mixed short fiber composites and estimated the27

optimum fiber length and fiber loading. They dealt with the

properties of randomly mixed palmyra fiber and glass fiber

reinforced rooflite hybrid composites. Mechanical properties

such as tensile, impact, shear and bending properties of the

composites were studied. The mechanical properties of the

composites are found to be improved on account of the

hybridization of the fibers used for reinforcement. The

composites reinforced with 50mm fibers and having a fiber

loading of 50% were found to have the best mechanical

properties. The properties were found to be increasing

continuously due to the addition of the glass fibers. It was

also found that the water absorption decreases considerably

with the addition of glass fibers.

Joshi et al (2009) investigated the effect of

hybridization of chopped glass fibers with small amounts of

mineral fibers. It was found that hybridization makes the

glass fiber composites more suitable for technical

applications. This study was based on the performance of

polypropylene based short wollastonite fiber (injection

molded) and chopped glass fiber reinforced hybrid composites.

Results showed that properties of the hybrid glass fiber and

wollastonite composite was found to be comparable to that of

polypropylene glass fiber composites. Fiber length

distribution and fracture surface analysis was done to study

the fiber breakage fracture mechanism. It was found that the

tensile, flexural, and impact properties of the filled

28

polypropylene were considerably higher than those of unfilled

polypropylene composites. With the addition of 30% glass

fibers, the tensile strength, flexural strength, tensile

modulus and the flexural modulus increased sharply in contrast

to non-hybrid composites. This showed the stiffening effect of

the glass fibers. On the other hand, the addition of the

wollastonite fibers from 10% to 30%, the above values

decreased gradually.

Athijayamani et al (2009) studied the variation of

mechanical properties of roselle and sisal fibers hybrid

polyester composite at dry and wet conditions were studied.

Properties such as tensile, flexural, and impact strengths

were taken into consideration. The composites of roselle/sisal

polyester-based hybrid composites with different weight

percentages of fibers were prepared. Roselle and sisal fibers

at a ratio of 1:1 had been incorporated in unsaturated

polyester resin at various fiber lengths. They found that when

the fiber content and length of the roselle and sisal fibers

were increased, the tensile and flexural strength of the

composite increased.

Valente et al (2011) studied the mechanical properties of

recycled glass fiber wood flour reinforced composites. The

properties studied included flexural modulus and strength,

hardness (which was studied as a function of temperature),

screw withdrawal resistance and water absorption behavior. It

was fond that the flexural modulus and hardness increased as a29

function of increasing wood flour and glass fiber content. In

contrast, the flexural strength and screw withdrawal

resistance decreased as a function of increasing wood flour

content, although the resistance was unaffected by wood flour

content up to 35 wt%. Although it was found that the addition

of glass fibers has a positive effect.

Thwe et al compared the fatigue behavior under cyclic

tensile load and the hygrothermal ageing of Bamboo fiber

reinforced polypropylene (BFRP) and bamboo Glass fiber

reinforced polypropylene (BGRP). The results showed that with

respect to stiffness and retention of tensile strength, the

BGRP samples have better resistance to environmental ageing as

compared to BFRP composites. It also showed that the BGRP has

better fatigue resistance than the BFRP composites at all load

levels. Thus it shows the improvement in the mechanical

properties due to hybridization.

Nayak et al studied the effect of addition of bamboo-

glass fiber reinforcements to the polypropylene matrix (BGRP).

Comparisons were made between the BGRP and the virgin

polypropylene. Fiber loading was taken as a parameter. Results

showed that the composites prepared at 30% fiber loading with

2% MAPP concentration showed optimum mechanical performance.

As compared to the virgin polypropylene, at a glass fiber:

bamboo concentration of 15:15, the tensile strength, flexural

strength and the impact strength increased by around 69%, 86%

30

and 83% respectively. Also, in the case of BGRP, less fiber

pullout was noticed in case of hybrid composites.

Rao et al studied the effect of bamboo/glass fibers

reinforcement in the epoxy matrix on the flexural and

compressive properties. These hybrid composites were found to

exhibit good flexural and compressive properties. The effect

of alkali treatment on these fibers was also studied.

Motahhari and Cameron reported that fiber prestressing

increased the impact strength of composites up to an optimum

prestress level of 60 MPa prestress and above this level, it

decreased. The authors’ explanation was that as the fiber

prestress increased the debonding fracture overcame the

transverse fracture, resulting in the formation of new large

surface areas, which absorbed more energy. Above a critical

limit of prestress (60 MPa), the impact properties declined as

the ability of the interface to resist shear debonding

decreased. The author’s suggested that the increase in the

resistance to transverse fracture of the matrix could be due

to the reduction in matrix residual stresses. As a result, the

fracture mode changes from transverse to interfacial

debonding, leading to more energy absorption. Fancey studied

the effect of viscoelastically-induced prestress on impact

properties of composites. In his work, Nylon fibers were

stretched under a load, which was released prior to matrix

impregnation. On solidification of the matrix, the

viscoelastically-strained fibers impart compressive stresses.31

From their results of charpy impact test they have shown that

prestressed composites absorb 25% more impact energy than non-

prestressed composites.

3. METHODOLOGY AND MODELLING

3.1 Experimental Analysis

In this project, the composite material is subjected to

fatigue and fracture analysis using Peripheral interface

Control (PIC) with embedded advanced C++ program. The material

property of the glass fiber composite material is found out

using compression load test.

The glass fiber composite material of dimensions 30 x 30 cm

with six layers is manufactured by hand layup method. Epoxy

32

resin is used to create bond between the layers. The figure.1

shows the model of the glass fiber composite.

Figure.1 – Glass fiber reinforced composite laminate

Now the glass fiber material is tested for its compression

mechanical properties using compression load test under ASTM

guidelines. Under ASTM guidelines the composite material test

size for compression load test is 7.5 x 6 cm, so the test

material is cut down to the specified dimensions above.

Then the compression test is carried out by placing the

layers of glass fiber composites on the test bed of the

compression load testing machine. Load is gradually applied

through the test material and the fracture point of the

material is found out until the material fractures. The table

33

below shows the load at which the fracture for the glass

composite materials.

Table .1 Dimensions of Glass Fiber Reinforced Composite

Laminate

S. No. Material Type Size(cm) Fracture Point

Load(kN)

1 Glass Fiber

composite

30 x 30 2880

The figure.2 shows the fracture in glass fiber reinforced

composite laminate that starts from the edges and then run

inwards.

34

Figure.2 – Fracture in glass fiber reinforced composite

laminate

The above results are compared with the numerical

analysis using ANSYS 14.0 Mechanical APDL.

3.2 Numerical Analysis

Various phenomena treated in science and engineering are

often described in terms of differential equations formulated

by using their continuum mechanics models. Solving

differential equations under various conditions such as

boundary or initial conditions leads to the understanding of

the phenomena and can predict the future of the phenomena

(determinism). Exact solutions for differential equations,

however, are generally dif cult to obtain. Numerical methodsfi

are adopted to obtain approximate solutions for differential

equations.

ANSYS is a general-purpose nite-element modeling packagefi

for numerically solving a wide variety of mechanical problems.

These problems include static/ dynamic, structural analysis

(both linear and nonlinear), heat transfer, and uid problems,fl

as well as acoustic and electromagnetic problems.

35

The numerical analysis in ANSYS Mechanical APDL involves

the following steps.

Modelling

Preprocessing

Setup

Postprocessing

3.3 Modelling

Modelling of the glass fiber composite laminate is done

using ANSYS and the model is shown below in the figure.3. The

glass fiber composite laminate is modelled after the specimen

which is used for the experimental calculation.

Table.2 – Dimensions of Modelled Glass fiber composite

laminate

Parameter Dimension

Length 30 cm

Width 30 cm

Thickness 0.5 mm per lamina

36

Figure.3 – Isometric view of glass fiber composite layers

Figure.4 – Side view of glass fiber composite layers

37

Figure.5 – Front view of glass fiber composite layers

Figure.6 – close up view of glass fiber composite layers

3.4 Preprocessing

Preprocessing involves setting up the model to structural

analysis and here h-model is used. Material properties are

38

required for most element types. Depending on the application,

material properties may be linear or nonlinear, isotropic,

orthotropic or anisotropic, constant temperature or

temperature dependent. As with element types and real

constants, each set of material properties has a material

reference number. The table of material reference numbers

versus material property sets is called the material table. In

one analysis there may be multiple material property sets

corresponding with multiple materials used in the model. Each

set is identi ed with a unique reference number. Althoughfi

material properties can be de ned separately for each nite-fi fi

element analysis, the ANSYS program enables storing a material

property set in an archival material library le, thenfi

retrieving the set and reusing it in multiple analyses. Each

material property set has its own library le. The materialfi

library les also make it possible for several users to sharefi

commonly used material property data. The mechanical

properties like young’s modulus and Poisson ratio are given as

input to define the mechanical behavior of the glass fiber

composites.

Table.3 – Mechanical Properties of Glass Fiber composite

laminates

Young’s Modulus 9.38 x 10^6

Poisson Ratio 0.23

39

Figure.7 – Mechanical properties of glass fiber composites

Then the model is meshed using the meshing command from

the preprocessor.

A mesh is a manifold if

(1) Each edge closed fan is incident to only one or two faces

and

(2) The faces incident to a vertex form a closed or an open

fan.

Since meshes are usually large and complex and since many

operations are performed on meshes, compact data structures

that support efficient algorithms are provided.

The meshed model is shown in the figure below.

40

Figure.8 – Meshed model of glass fiber composites

Figure. 9 – Close up view of mesh of glass fiber composite

3.4 Setup

41

It is necessary to de ne the analysis type and analysisfi

options, apply loads, specify load step options, and initiate

the nite-element solution. The analysis type to be used isfi

based on the loading conditions and the response which is

wished to calculate.

The desired load of 2880 kN is applied as uniformly

distributed load over the top surface of the glass fiber

composite to simulate the compression test. The lower surface

of the glass fiber composite is fixed and the degrees of

freedom for the lower surface is considered to be zero.

Figure.10 –

Fixed lower

surface of

the glass

fiber

composites

Figure.11 –

Application

of Load on

the upper surface of glass fiber composites

The setup is now solved using current load setup and the

results are calculated.

42

3.5 Postprocessing

The results are calculated and plotted for the fracture

point load.

Figure.12 – Distribution of Fracture point load on glass fiber

composites

The above figure.12 shows the distribution of load on the

glass fiber composite laminates. From the figure it can be

found out that the maximum load is acting on the corner of the

laminates and thus the fracture starts only at the corners of

the laminates and then propagates to the inner part of the

glass fiber laminates.43

Figure.13 – Deformation of glass fiber composites with

undeformed structure

The above figure.13 shows and compares the deformation of

glass fiber composite laminate with undeformed structure.

Since the lower fixed and the load is applied from the upper

surface, it is clear that the deformation of glass fiber

composite laminate is maximum only at the upper surface.

44

4. Setup for Predetermination of Fatigue And Fracture In Glass

Fiber Composite Laminate

45

4.1 Block Diagram

Power cell

LCD DISPLAY

LOAD CELL

PIC BUZZER

16F877A

MICRO

CON

TROLLER GREEN LED

RED LED

(ABNORMAL)

Figure.14 – Schematic Diagram of Setup for Predetermination of

Fatigue and Fracture in Glass Fiber Composite Laminate

46

4.2 Load Cell Working

Load cell is a passive transducer or sensor which

converts applied force into electrical signals. The resistance

of strain gauge changes when its length changes. This change

in resistance can be measured in terms of change in output

voltage and amplify using differential amplifier. If the

voltage comes to be negative, the inverter makes it positive.

Thus, a load cell gives us a voltage level equivalent to the

weight applied.

Here The Controlling device of the whole system is a

Microcontroller. The data from the load cell sensor are

processed and displayed on to a LCD. Also, the Microcontroller

continuously monitors the load cell output value and judges

whether the product weight normal means it alerts through LED

indicators otherwise abnormal means the buzzer will be on.

4.3 Softwares Used

1. PIC-C compiler for Embedded C programming.

2. MPLAB IDE v8.56

3. PIC kit 3 Programmer for dumping code into Micro

controller.

4.4 Hardware Description

1) LOAD CELL

2) PIC MICROCONTROLLER 16F877A

3) POWER SUPLY

4) LCD DISPLAY

5) BUZZER AND LED INDICATORS

4.5 Load cell 47

A load cell is a sensor or a transducer that

converts a load or force acting on it into an electronic

signal. This electronic signal can be a voltage change,

current change or frequency change depending on the type of

load cell and circuitry used.

Load cells or Load sensors as they are commonly

called - can be made using resistive, capacitive, inductive or

other techniques. Most commonly available load cells are based

on the principle of change of resistance in response to an

applied load. This is termed piezo-resistive i.e. something

that changes in response to an applied pressure (or squeezed).

Loadstar Sensors has pioneered the use of capacitive

techniques to build rugged, small digital load cells with high

level USB, WiFi, XBee Wireless and Bluetooth outputs. We have

over a dozen patents covering various aspects of capacitive

and digital load cells. We have also developed a variety of

convenient low cost easy to use, digital and analog interfaces

that enable incorporation of load cells and other sensors into

a variety of applications.

Commonly available load cells include:

- S-Beam Load Cell - Single Point Load Cells - Shear Beam Load

Cells - Pancake Load Cells - Button Load Cells - Through hole

Load cells and - Miniature and Sub-Miniature load cells

4.6 Characteristics of Load Cell

1. Highly precise and linear measurements

2. Little influence due to temperature changes.

48

Figure.14 - PIC 16F877

3. Long operating life due to lack of moving parts or any

parts that generate friction.

4. Ease in production due to small number of components.

5. Excellent fatigue characteristics

Available load cells are 6 Kg., 10 Kg., 20 Kg., 40 Kg.,

80 Kg and others. Out of these available load cells we will

choose 6 Kg. load cell as it satisfies all the requirements.

4.7 Pic Micro Controller

PIC 16F877 is one of the most advanced microcontroller

from Microchip. This controller is widely used for

experimental and modern applications because of its low price,

wide range of applications, high quality, and ease of

availability. It is ideal for applications such as machine

control applications, measurement devices, study

Purpose, and so on. The PIC 16F877 features all the

components which modern microcontrollers normally have. The

figure of a PIC16F877 chip is shown below.

4.8 Features of PIC16f877

The PIC16FXX series has more advanced and developed features

when compared to its previous series. The important features

of PIC16F877 series is given below.

4.9 General Features

High performance RISC CPU.

ONLY 35 simple word instructions.

49

All single cycle instructions except for program branches

which are two cycles.

Operating speed: clock input (200MHz), instruction cycle

(200nS).

Up to 368×8bit of RAM (data memory), 256×8 of EEPROM (data

memory), 8k×14 of flash memory.

Pin out compatible to PIC 16C74B, PIC 16C76, PIC 16C77.

Eight level deep hardware stack.

Interrupt capability (up to 14 sources).

Different types of addressing modes (direct, Indirect,

relative addressing modes).

Power on Reset (POR).

Power-Up Timer (PWRT) and oscillator start-up timer.

Low power- high speed CMOS flash/EEPROM.

Fully static design.

Wide operating voltage range (2.0 – 5.56) volts.

High sink/source current (25mA).

Commercial, industrial and extended temperature ranges.

Low power consumption (<0.6mA typical @3v-4MHz, 20µA typical

@3v32MHz and <1 A typical standby).

4.10 Key Features

Maximum operating frequency is 20MHz.

Flash program memory (14 bit words), 8KB.

Data memory (bytes) is 368.

EEPROM data memory (bytes) is 256.

5 input/output ports.

3 timers. 50

2 CCP modules.

2 serial communication ports (MSSP, USART).

PSP parallel communication port

10bit A/D module (8 channels)

4.11 Analog Features

10bit, up to 8 channel A/D converter.

Brown out Reset function.

Analog comparator module.

4.12 Special Features

100000 times erase/write cycle enhanced memory.

1000000 times erase/write cycle data EEPROM memory.

Self programmable under software control.

In-circuit serial programming and in-circuit debugging

capability.

Single 5V, DC supply for circuit serial programming

WDT with its own RC oscillator for reliable operation.

Programmable code protection.

Power saving sleep modes.

Selectable oscillator options.

51

Figure.15 - PIN Diagram

4.13 PIN Diagram

4.14 Input/output Ports

52

PIC16F877 has 5 basic input/output ports. They are

usually denoted by PORT A (R A), PORT B (RB), PORT C (RC),

PORT D (RD), and PORT E (RE). These ports are used for input/

output interfacing. In this controller, “PORT A” is only 6

bits wide (RA-0 to RA-7), ”PORT B” , “PORT C”,”PORT D” are

only 8 bits wide (RB-0 to RB-7,RC-0 to RC-7,RD-0 to RD-7),

”PORT E” has only 3 bit wide (RE-0 to RE-7).

All these ports are bi-directional. The direction of

the port is controlled by using TRIS(X) registers (TRIS A used

to set the direction of PORT-A, TRIS B used to set the

direction for PORT-B, etc.). Setting a TRIS(X) bit „1‟ will

set the corresponding PORT(X) bit as input. Clearing a TRIS(X)

bit „0‟ will set the corresponding PORT(X) bit as output.

(If we want to set PORT A as an input, just set TRIS (A) bit

to logical „1‟ and want to set PORT B as an output, just set

the PORT B bits to logical „0‟.)

Analog input port (AN0 TO AN7): these ports are used for

interfacing analog inputs. TX and RX: These are the USART

transmission and reception ports.

SCK: these pins are used for giving synchronous serial clock

input.

SCL: these pins act as an output for both SPI and I2C modes.

DT: these are synchronous data terminals.

CK: synchronous clock input.

SD0: SPI data output (SPI Mode).

SD1: SPI Data input (SPI mode).

SDA: data input/output in I2C Mode. 53

CCP1 and CCP2: these are capture/compare/PWM modules.

OSC1: oscillator input/external clock.

OSC2: oscillator output/clock out.

MCLR: master clear pin (Active low reset).

Vpp: programming voltage input.

THV: High voltage test mode controlling.

Vref (+/-): reference voltage.

SS: Slave select for the synchronous serial port.

T0CK1: clock input to TIMER 0.

T1OSO: Timer 1 oscillator output.

T1OS1: Timer 1 oscillator input.

T1CK1: clock input to Timer 1.

PGD: Serial programming data.

PGC: serial programming clock.

PGM: Low Voltage Programming input.

INT: external interrupt.

RD: Read control for parallel slave port.

CS: Select control for parallel slave.

PSP0 to PSP7: Parallel slave port.

VDD: positive supply for logic and input pins.

VSS: Ground reference for logic and input/output pins.

4.15 LCD Display

Liquid crystal display i.e. LCD is used for display

purpose. A 16 x 2 LCD is used to display results in 4 bit

mode.

The output voltage is converted into digital form and

displayed on LCD. 54

Figure.16 - LCD Display

Figure 17 – Power Supply Circuit Diagram

POWER SUPPLY BLOCK DIAGRAM

The input to the circuit is applied from the regulated

power supply. The a.c. input i.e., 230V from the mains supply

is step down by the transformer to 12V and is fed to a

rectifier. The output obtained from the rectifier is a

pulsating d.c voltage. So in order to get a pure d.c voltage,

the output voltage from the rectifier is fed to a filter to

remove any a.c components present even after rectification.

Now, this voltage is given to a voltage regulator to obtain a

pure constant DC voltage.

4.16 Power Supply Circuit Diagram

55

56

This is a simple approach to obtain a 12V and 5V DC

power supply using a single circuit. The circuit uses two ICs

7812(IC1) and 7805 (IC2) for obtaining the required voltages.

The AC mains voltage will be stepped down by the transformer

T1, rectified by bridge B1 and filtered by capacitor C1 to

obtain a steady DC level .The IC1 regulates this voltage to

obtain a steady 12V DC. The output of the IC1 will be

regulated by the IC2 to obtain a steady 5V DC at its output.

In this way both 12V and 5V DC are obtained.

Such a circuit is very useful in cases when we need two

DC voltages for the operation of a circuit. By varying the

type number of the IC1 and IC2, various combinations of output

voltages can be obtained. If 7805 is used for IC2, we will get

6V instead of 5V.Same way if 7809 is used for IC1 we get 9V

instead of 12V.

4.17 Buzzer and Led Indicators

Buzzer and led indicators are used to indicate the status

(normal, abnormal values) of the load cell.

In this project, we developed PIC microcontroller based

Electronic Weighing Machine. We have used load cell for

measurement of weight. We have used load cell for measurement

of weight. The transducer used is a foil strain gauge based

load cell mounted to operate by the bending principle. This

system is more accurate than analog scale weighing machine.

57

We can measure the weight of ingedients. Weight

measurement is used in shops, vegetable shop, jewelry shop,

hotels. Electronic weighing technology presents management

with rapid, timely and accurate information that provides

quick turnaround times for customers.

The developed microcontroller based electronic weighing

balance has following advantages:

1. Low-cost, flexible and portable. This system is able to

measure mass in the range of 0 to 6kg

2. As Pic Microcontroller has inbuilt ADC, size is compact.

3. Accuracy is more.

This can be used for

1. Load checking

2. Weight

3. Strain Gauge

4.18 Setup for Predetermination of Fatigue And Fracture In

Glass Fiber Reinforced Composite Laminate

A setup for predetermination of fatigue and fracture in glassfiber reinforced laminate is shown below in the figure.18 .Thedisplay will indicate the load applied to the composite materiallaminates and the red light indicator acts as the indicatormaximum load which is coded with PIC controllers.

58

Figure.18 - Setup for Predetermination of Fatigue andFracture in Glass Fiber Reinforced Composite Laminate

A load cell is attached to the composite laminates that

will transfer the amount of applied load on the composite

laminate to the controllers.

59

Figure.19 – Glass fiber reinforced composite laminate attached

to a load cell

To test the setup an optimal load of 4 kgs is set to thecontrollers. When the load is gradually applied on the glassfiber reinforced composite laminates from the outer surface.

As the load is applied gradually the green lightindicator will glow as show in the figure.20.

Figure.20 – Green light indicates the applied load is below 4kgs.

When the applied load reaches 4 kgs or exceeds theoptimal load conditions the red light indicator will glow asshown in the figure. - .

60

Figure.21 – As the load reaches 4kgs. Red light indicator

glows

Thus a successful attempt is made that clearly show the

capability of the setup to predetermine the fracture load that

could occur in real flight conditions.

61

5. RESULT AND DISCUSSION

The results from the experimental and numerical analysis

of glass fiber reinforced composite subjected to fracture load

are compared and discussed. A setup for the predetermination

of the fracture and fatigue loads is done using load cell

based weighing scale that uses PIC controller. This type of

predetermination will be useful for the pilot to prevent

structural damages that could occur on flight to the aircraft

structural components due to some sudden load conditions like

gust or due to over air speed.

62

6. REFERENCES

[1]. “PIC Microcontroller and Embedded Systems”, By Mazidi,

Mckinlay and

Causey.

[2]. “Mechanical and Industrial Measurements”, By R. K. Jain,

Khanna Publishers.

[3]. Belove, C. (1986), Handbook of Modern

Electronics and Electrical Engineering, John Wiley

and Sons Inc. U.S.A.

[4].www.fairchildsemi.com

[5].www.microchip.com

[6]. Belove, C. (1986), Handbook of Modern

Electronics and Electrical Engineering, John Wiley

and Sons Inc. U.S.A., pp 2-19.

63

[7]. Bentley, J. P., Measurement Systems, Addison Wesley

Longman Ltd., UK, 2000.

[8]. Borer, J. (1991), Microprocessor in Process Control,

University Press Great Britain, pp 21-30.

[9]. Braby, P. W., Electronics: A Practical Introduction,

John Wiley & Sons, Canada Limited, 1983.

[10]. Brophy, J.J. (1990) Basic Electronics for

Scientists, McGraw-Hill International Editions,

fifth Edition, pp 462.

64