Leaf Springs

1

ABSTRACT

The automobile industry has shown increased interest in the

replacement of steel spring with fibre glass composite leaf spring due to

high strength to weight ratio. Therefore, the aim of this paper is to present

a low cost fabrication of complete mono composite leaf spring and mono

composite leaf spring with bonded end joints. Also, General study on the

analysis and design. A single leaf with variable thickness and width for

constant cross sectional area of unidirectional glass fibre reinforced

plastic (GFRP) with similar mechanical and geometrical properties to the

multi leaf spring, is to be designed. The results is to show that unsprung

width decreases hyperbolically and thickness increases linearly from the

spring eyes towards the axle seat. The finite element results using

ANSYS software showing stresses and deflections were to be verified

with analytical. The design constraints were stresses and displacement.

2

CONTENTS

CHAPTER TITLE PAGE

NO

ABSTRACT iii

LIST OF THE TABLES v

LIST OF CHARTS vi

LIST OF FIGURES vii

1. FEATURES OF LEAF SPRING 1

2. MATERIALS USED FOR MONO

COMPOSITE LEAF SPRING 13

3. DESIGN OF MONO COMPOSITE

LEAF SPRING 20

4. DESIGN OF LEAF SPRING 24

USING PRO-E

5. ANALYSIS OF STRESS AND

DISPLACEMENT USING ANSYS 32

6. GRAPH FOR STRESS AND

DEFLECTION 50

7. RESULTS 53

8. ADVANTAGES OF MONO

COMPOSITE LEAF SPRING 56

9. CONCLUSION 58

10. BIBLIOGRAPHY 60

3

LIST OF THE TABLES

TAB.NO. CONTENT PAGENO

1. Properties of steel leaf

45

2. Properties of A-Glass Fiber, Generic.

46

3. Properties of C-Glass Fiber, Generic.

47

4. Properties of D-Glass Fiber, Generic 48

5. Properties of E-Glass Fiber, Generic

49

6. Comparison results of stresses

51

7. Comparison results of deflection

52

8. Comparison results of load, deflection and

stresses

55

4

LIST OF THE CHARTS

CH.NO. CONTENT PAGENO

1. Comparison chart for stress & materials

51

2. Comparison chart for deflection & materials

52

5

LIST OF THE FIGURES

FIG.NO. CONTENT PAGENO

1. Leaf spring 2

2. Molecular Structure of Glass

16

3. Sketch of leaf. 30

4. Part of leaf 30

5. Sketch of steel leaf 31

6. Part of steel leaf 31

7. Pro E Model 35

8. FEA Model 36

9. FEA load set 40

6

10. FEA Mesh 42

11. Stress distribution for steel leaf 45

12. Stress distribution for A-Glass Fiber leaf

spring

46

13. Stress distribution for C-Glass Fiber leaf

spring

47

14. Stress distribution for D-Glass Fiber leaf

spring

48

15. Stress distribution for E-Glass Fiber leaf spring 49

7

CHAPTER-1

FEATURES OF LEAF SPRING

8

LEAF SPRING

INTRODUCTION:

Material becomes a major factor in designing the springs. In order

to conserve natural resources and economize energy, weight reduction

has been the main focus of automobile manufacturer in the present

scenario. Weight reduction can be achieved primarily by the introduction

of better material, design optimization and better manufacturing

processes. The suspension leaf spring is one of the potential items for

weight reduction in automobile as it accounts for ten to twenty percent of

the un sprung weight. This helps in achieving the vehicle with improved

riding qualities. It is well known that springs, are designed to absorb and

store energy and then release it. Hence, the strain energy of the

relationship of the specific strain energy can be expressed as

^2

U= --------

E

Where is the strength, the density and E the Youngs

modulus of the spring material. It can be easily observed that material

having lower modulus and density will have a greater specific strain

energy capacity. The introduction of composite materials was made it

possible to reduce the weight of the leaf spring with out any reduction on

load carrying capacity and stiffness. Since; the composite materials have

more elastic strain energy storage capacity and high strength-to-weight

ratio as compared to those of steel.

Several papers were devoted to the application of composite

materials for automobiles. It studied the application of composite

structures for automobiles and design optimization of a composite leaf

9

spring. Great effort has been made by the automotive industries in the

application of leaf springs made from composite materials. It showed the

introduction of fiber reinforced plastics (FRP) made it possible to reduce

the weight of a machine element with out any reduction of the load

carrying capacity. Because of FRP materials high elastic strain energy

storage capacity and high strength-to-weight ratio compared with those of

steel, multi-leaf steel springs are being replaced by mono leaf FRP

springs. In every automobile, i.e. four wheelers and railways, the leaf

spring is one of the main components and it provides a good suspension

and it plays a vital role in automobile application. It carries lateral loads,

brake torque, driving torque in addition to shock absorbing. The

advantage of leaf spring over helical spring is that the ends of the spring

may be guided along a definite path as it deflects to act as a structural

member in addition to energy absorbing device.

The geometry of the Steel leaf spring is shown in Fig.1.

10

DEFINITION

Leaf springs are also called laminated, semi-elliptical, carriage

springs, cart spring, or helper spring. These are the simplest form of

spring, commonly used for the suspension in vehicles.

These are an example of one of the oldest forms of spring making,

dating back to medieval times. This type of spring is made from flat

spring steel of rectangular cross-section. The steel is formed into an arc.

The center of the arc provides the location for the axle, while tie

holes are provided at either end for attaching to the vehicle body. For

very heavy vehicles it is normal for several leaves to be stacked on top of

each other in several layers, often with systematically shorter leaves.

These springs were very common on automobiles up the mid

1970's. Now most designs of automobile manufacturers use coil springs,

gas springs, or air suspension instead.

They are still used in heavy commercial vehicles such as vans and

trucks, and rail cars. For heavy vehicles, they have the advantage of

spreading the load more widely over the vehicle's chassis, whereas coil

springs transfer it to a single point.

Unlike coil springs, these springs also locate the rear axle,

eliminating the need for trailing arms and a Pan hard rod, thereby saving

cost and weight in a simple live axle rear suspension.

Elliptical or full elliptical springs refer to two circular arcs linked

at their tips. These are joined to the frame at the top center of the upper

arc. The bottom center is joined to the suspension components, such as a

11

solid front axle. Additional suspension components, such as trailing arms,

are needed for this design.

Semi-elliptical springs use a lower arc. Therefore, they don't need

the additional suspension components.

Quarter-elliptical springs have the thickest part of the stack of

leaves stuck into the rear end of the side pieces of a ladder type frame.

The free end is attached to the differential.

An example of non-elliptical springs of this type is the Ford Model

T. It had multiple springs over its differential that were curved in the

shape of a yoke. As a substitute for dampers (shock absorbers), some

manufacturers laid wood sheets in between the metal leaves.

A newer design is the parabolic leaf spring. This design uses

fewer leaves. The thickness of the leaves vary from center to end

following a parabolic curve. Friction between the leaves is not wanted. So

there is only contact between the springs at the ends and at the center

where the axle is connected. Spacers prevent contact at other points.

The advantages of this type design are weight saving and greater

flexibility. They can come very close to the same performance of coil

springs.

12

Motion of a transverse leaf spring

The following images show the movements of an independent

suspension using a transverse leaf spring. For all images:

The suspension arms are green

The chassis is blue

The uprights are gray

Leaf springs are dark gray

Pivot links connecting the ends of the springs to the suspension

arms are red

1 - A transverse leaf spring

suspension at rest, with separate

right and left springs.

2 - The same split-spring

configuration with the left wheel in

compression.

Illustrations #1 and #2 show independent left and right leaf springs

mounted rigidly to a chassis. In the first illustration, the suspension is at

rest. As a left wheel moves up in the second illustration, the left spring

flexes upward, but the right spring remains unaffected. Because the two

springs are not connected, the movement of one wheel has no effect on

the spring rate of the opposite wheel. While the C2, C3 andC4 Corvettes

used a continuous spring instead of the split spring of the illustration, left

and right spring rates remained independent because the spring was

rigidly mounted at its center to the chassis.

13

3 - A single transverse leaf spring

suspension similar to that used on the

C5 and C6 Corvette.

4 - The same single-leaf

suspension with both wheels

compressed upward.

Illustrations #3 and #4 show an independent suspension with a

single transverse leaf spring, an arrangement similar to that used on the

C5 and C6 Corvettes and the front of the C4 Corvette. While at rest in

illustration #3, the leaf forms a symmetric arc between the left and right

sides of the suspension with equal force applied to each. Under the

compression of both wheels in illustration #4, the widely-spaced chassis

mounts allow the spring to pivot; the ends of the spring flex upward and

the center moves down. Spring force remains even between both sides.

At static ride height the leaf spring

applies the same 300lb to each side

of the suspension.

In compression the spring force has

increased to 500lb but is still even

between both sides

The leaf spring as an anti-roll bar

The extent to which a leaf spring acts as an anti-roll bar is

determined by the way it is mounted. A single, loose center mount would

cause the spring to pivot about the center axis, pushing one wheel down

as the other was compressed upward. This is exactly opposite of an anti-

roll bar and has not been used on any generation of the Corvette.

A single, perfectly rigid center mount that held a small center

section of the spring flat against the frame would isolate one side of the

spring from the other. No roll or anti-roll effect would appear. The rear

14

spring of the C2, C3, and C4 has this type of mount, which effectively

divides the spring in two. It becomes a quarter-elliptic spring.

A single transverse

spring with a

flexible center

mount. When one

side is pushed up the

other side moves

down.

A transverse leaf

spring with a semi-

rigid mount. When

one side is pushed

up the other side

moves down

significantly less

than in the flexible

mount case.

A transverse leaf

spring with a central

rigid mount. The two

spring halves are

effectively isolated.

Movements of one half

of the spring do not

affect the other half.

Beginning with the C4 model, the Corvette has had widely-spaced

double mounts on the front. The rear spring has had double mounts since

the C5. The spring is allowed to pivot about these two points. When only

one wheel is compressed as in illustration #5, the portion of the spring

between the mounts assumes a horizontal "S" shape. An impact that

compresses the left wheel will tighten the bend radius of the right half of

the spring, thereby lowering the spring rate for the right wheel like an

anti-roll bar. The caster, camber, toe-in, and general orientation of the left

wheel remain unchanged.

5 - The single-leaf suspension with the

left side in compression.

5a - The same suspension

in rear profile.

15

With the Corvette's suspension configuration, the effects of the

anti-roll bar and leaf spring add together at the wheels. This additive

property allows Corvette engineers to use a smaller, lighter anti-roll bar

than the car would otherwise require if it used conventional coil springs.

From Dave McClellan, chief engineer on the C4 Corvette program:

We planned to use a massive front [roll] bar to achieve the roll

stiffness we were after. We found, however, that by spreading the body

attachment of the front suspension fiberglass spring into two separate

attachments 18 inches apart, we could achieve a major portion of the roll

stiffness contribution of the front roll bar for free. We still used a massive

front bar, but it would have been even bigger and heavier if it had not

been supplemented by the leaf spring.

This multi exposure

image shows an

exaggerated view

of the leaf spring

flex when the

wheels are

compressed, in

droop and in roll.

The S-bent spring

is shown in blue.

Left side shown in

compression, right

side shown at static

height. The left side

spring force has

increased from

500lbs to 600lbs

while the right side

has decreased from

300lb to 200lb.

Approximate FEA

model of a leaf spring

under load. The

initial, unbent shape

of the spring is shown

as a silhouette box.

An upward deflection

on the right side of

the spring results in a

smaller upward

movement on the left

side.

16

Advantages:

Less unsprung weight. Coil springs contribute to unsprung weight;

the less there is, the more quickly the wheel can respond at a given

spring rate.

Less weight. The C4 Corvette's composite front leaf weighed 1/3 as

much as the pair of conventional coil springs it would replace.

Volvo reported that the single composite leaf spring used in the

rear suspension of the 960 Wagon had the same mass as just one of

the two springs it replaced.

Weight is positioned lower. Coil springs and the associated chassis

hard mounts raise the centre of gravity of the car.

Superior wear characteristics. The Corvette's composite leaf

springs last longer than coils, though in a car as light as the

Corvette, the difference is not especially significant. No composite

Corvette leaf has ever been replaced due to fatigue failure, though

steel leafs from 1963 to 1983 have been. As of 1980, the composite

spring was an option on the C3.

As used on the Corvette, ride height can be adjusted by changing

the length of the end links connecting the leaf to the suspension

arms. This allows small changes in ride height with minimal effects

on the spring rate.

17

Also as used on the C4 front suspension, C5, and C6 Corvettes, the

leaf spring acts as an anti-roll bar, allowing for smaller and lighter

bars than if the car were equipped with coil springs. As

implemented on the C3 and C4 rear suspensions with a rigid

central mount, the anti-roll effect does not occur.

Packaging. As used on the C5 and later Corvettes the use of OEM

coil over damper springs would have forced the chassis engineers

to either vertically raise the shock towers or move them inward. In

the rear this would have reduced trunk space. In the front this

would have interfered with engine packaging. The use of the leaf

spring allowed the spring to be placed out of the way under the

chassis and while keeping the diameter of the shock absorber

assembly to that of just the damper rather than damper and spring.

18

Disadvantages:

Packaging can be problematic; the leaf must span from one side of

the car to the other. This can limit applications where the drive

train, or another part, is in the way.

Materials expense. Steel coils are commodity items; a single

composite leaf spring costs more than two of them.

Design complexity. Composite monoleafs allow for considerable

variety in shape, thickness, and materials. They are inherently more

expensive to design, particularly in performance applications.

Cost of modification. As a result of specialized design and

packaging, changing spring rates often requires a custom unit. Coil

springs in various sizes and rates are available inexpensively.

Susceptibility to damage. Engine fluids and exhaust modifications

like cat-back removal might weaken or destroy composite springs

over time. The leaf spring is more susceptible to heat related

damage than conventional steel springs.

Perception. Due to its association with spring-located solid axles,

the leaf spring has a stigma unrelated to the spring itself.

19

CHAPTER-2

MATERIALS USED FOR MONO

COMPOSITE LEAF SPRING

20

MATERIALS USED FOR MONO COMPOSITE LEAF

SPRING

Fiberglass

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. Glassmakers throughout

history have experimented with glass fibers, but mass manufacture of

fiberglass was only made possible with the invention 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. This was first worn by the popular

stage actress of the time Georgia Cayvan.

What is commonly known as "fiberglass" today, however, was

invented in 1938 by Russell Games Slayers of Owens-Corning as a

material to be used as insulation. It is marketed under the trade name

Fiberglas, which has become a generic zed trademark. A somewhat

similar, but more expensive technology used for applications requiring

very high strength and low weight is the use of carbon fiber.

Fiber formation

Glass fiber is formed when thin strands of silica-based or other

formulation glass is extruded into many fibers with small diameters

suitable for textile processing. The technique of heating and drawing

glass into fine fibers has been known for millennia; however, the use of

21

these fibers for textile applications is more recent. Until this time all

fiberglass had been manufactured as staple (a term used to describe

naturally formed clusters or locks of wool fibers). The first commercial

production of fiberglass was in 1936. In 1938 Owens-Illinois Glass

Company and Corning Glass Works joined to form the Owens-Corning

Fiberglas Corporation. When the two companies joined to produce and

promote fiberglass, they introduced continuous filament glass fibers.

Owens-Corning is still the major fiberglass producer in the market today.

The types of fiberglass most commonly used are mainly E-glass

(alumino-borosilicate glass with less than 1 wt% alkali oxides, mainly

used for glass-reinforced plastics), but also A-glass (alkali-lime glass with

little or no boron oxide), E-CR-glass (alumino-lime silicate with less than

1 wt% alkali oxides, has high acid resistance), C-glass (alkali-lime glass

with high boron oxide content, used for example for glass staple fibers),

D-glass (borosilicate glass with high dielectric constant), R-glass

(alumino silicate glass without MgO and CaO with high mechanical

requirements), and S-glass (alumino silicate glass without CaO but with

high MgO content with high tensile strength).

Chemistry

The basis of textile-grade glass fibers is silica, SiO2. In its pure

form it exists as a polymer, (SiO2)n. It has no true melting point but

softens at 2,000 C (3,630 F), where it starts to degrade. At 1,713 C

(3,115 F), most of the molecules can move about freely. If the glass is

then cooled quickly, they will be unable to form an ordered structure. In

the polymer, it forms SiO4 groups which are configured as a tetrahedron

with the silicon atom at the center and four oxygen atoms at the corners.

22

These atoms then form a network bonded at the corners by sharing the

oxygen atoms.

The vitreous and crystalline states of silica (glass and quartz) have

similar energy levels on a molecular basis, also implying that the glassy

form is extremely stable. In order to induce crystallization, it must be

heated to temperatures above 1,200 C (2,190 F) for long periods of time

fig.2: Molecular Structure of Glass

Although pure silica is a perfectly viable glass and glass fiber, it

must be worked with at very high temperatures, which is a drawback

unless its specific chemical properties are needed. It is usual to introduce

impurities into the glass in the form of other materials to lower its

working temperature. These materials also impart various other properties

to the glass which may be beneficial in different applications. The first

type of glass used for fiber was soda lime glass or A-glass. It was not

very resistant to alkali. A new type, E-glass, was formed; this is an

alumino-borosilicate glass that is alkali free (

23

strength is the most important property. C-glass was developed to resist

attack from chemicals, mostly acids which destroy E-glass. T-glass is a

North American variant of C-glass. A-glass is an industry term for cullet

glass, often bottles, made into fiber. AR-glass is alkali-resistant glass.

Most glass fibers have limited solubility in water but are very dependent

on pH. Chloride ions will also attack and dissolve E-glass surfaces.

Since E-glass does not really melt, but soften, the softening point is

defined as "the temperature at which a 0.550.77 mm diameter fiber 235

mm long, elongates under its own weight at 1 mm/min when suspended

vertically and heated at the rate of 5C per minute". The strain point is

reached when the glass has a viscosity of 1014.5 poise. The annealing

point, which is the temperature where the internal stresses are reduced to

an acceptable commercial limit in 15 minutes, is marked by a viscosity of

1013 poise.

Properties:

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

the order of 0.05 W/(mK).

The strength of glass is usually tested and reported for "virgin" or

pristine fibersthose 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

24

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. There is a correlation between bending diameter of the

filament and the filament diameter. 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.

Glass-reinforced plastic:

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

reinforced plastic made of a plastic reinforced by fine glass fibers. Like

graphite-reinforced plastic, the composite material is commonly referred

to by the name of its reinforcing fibers (fiberglass). Thermosetting

plastics are normally used for GRP productionmost often unsaturated

polyester (using 2-butanone peroxide aka MEK peroxide as a catalyst),

but vinyl ester or epoxy are also used. Traditionally, styrene monomer

was used as reactive diluents in the resin formulation giving the resin a

characteristic odor. More recently alternatives have been developed. The

glass can be in the form of a chopped strand mat (CSM) or a woven

fabric.

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

25

materials, GRP becomes a material that resists both compressive and

tensile forces well. 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.

Uses:

Uses for regular fiberglass include mats, thermal insulation,

electrical insulation, reinforcement of various materials, tent poles, sound

absorption, heat- and corrosion-resistant fabrics, high-strength fabrics,

pole vault poles, arrows, bows and crossbows, translucent roofing panels,

automobile bodies, hockey sticks, surfboards, boat hulls, and paper

honeycomb. It has been used for medical purposes in casts. Fiberglass is

extensively used for making FRP tanks and vessels. Fiberglass is also

used in the design of Irish step dance shoes.

In the 1986 - 1987 America's Cup, New Zealand, with the help of

Rene Felcher, Bruce Farr, and Michael Fay, entered a boat whose hull

was made of the lighter fiberglass, nicknamed the Plastic Fantastic ",

and given the call sign KZ7. This caused a similar controversy and

protests as those generated four years earlier by Australia's used of

winged keels as designed by the now late Ben Lexcen. United States

sailor Dennis Conner was particularly critical of both new innovations in

their time. The boats proved fast on occasion, being much lighter than the

standard models, even those with winged keels, but the experience of

Conner allowed him to return the World's oldest sporting trophy to the

United States.

26

CHAPTER-3

DESIGN OF MONO COMPOSITE LEAF

SPRING

27

DESIGN OF LEAF SPRING

DESIGNS OF COMPOSITE MONO LEAF SPRING:

Considering several types of vehicles that have leaf springs and

different loading on them, various kinds of composite leaf spring have

been developed. In multi-leaf composite leaf spring, the interleaf spring

friction plays a spoil spot in damage tolerance. It has to be studied

carefully.

The following cross-sections of mono-leaf composite leaf spring

for manufacturing easiness are considered.

1. Constant thickness, constant width design.

2. Constant thickness, varying width design.

3. Varying width, varying thickness design.

PROCEDURE:

Width of the leaf spring, b

Thickness of the leaf, t

Length of the cantilever beam (spring), L

No. of leaves in the spring, n

Bending stress, b = 6PL nbt3

Deflection of spring, y = 6PL3

E nbt3

28

Load of the spring, P in N.

Youngs Modulus, E in N/mm2.

CALCULATION:

Width of the leaf spring, b = 50mm

Thickness of the leaf, t = 20mm

Length of the cantilever beam (spring), L = 520mm

No. of leaves in the spring, n = 1

Let us consider a load, P = 4000N

b = (6*4000*520) / (1*50*203)

= 624 MPa

YA-Glass= (6*4000*5203) / (68.9*103*1*50*203)

= 122.4 N/mm2

YC-Glass= (6*4000*5203) / (68.9*103*1*50*203)

= 122.4 N/mm2

YD-Glass= (6*4000*5203) / (51.7*103*1*50*203)

= 163.18 N/mm2

29

YE-Glass= (6*4000*5203) / (72.4*103*1*50*203)

= 116.5 N/mm2

SPECIFICATION OF THE PROBLEM:

The objectives of the present work is to design, analyze,

fabricate and testing of Unidirectional Glass Fiber/Epoxy complete mono

composite leaf spring without end joints and composite leaf spring using

bonded end joints using hand-lay up technique. This is an alternative,

efficient and economical method over wet filament-winding techniques.

Varying width, varying thickness design:

Parameters (mm) At centre At end

Breadth 45 69

Thickness 15 21

30

CHAPTER-4

DESIGN OF LEAF SPRING USING

PRO-E

31

DESIGN OF LEAF SPRING USING PRO-E:-

INTRODUCTION TO PRO-E:

Pro-ENGINEER is the worlds leading 3D product development

solution, which is developed by PTC-Parametric Technology

Corporation- a US based company. This software enables designers and

engineers to bring better product market faster. It takes care of enter

product development process, from creative concept through detailed

product definition to serviceability. Pro-EINGINEER delivers measurable

value to manufacturing companies of all sizes and in all industries.

Pro/ENGINEER is used in a vast range of industries, from

manufacturing of rockets to computer peripherals. With more than

100,000 seats install worldwide, many CAD users are exposed to

Pro/ENGINEER and enjoy using Pro/ENGINEER for its power and

capability.

The major elements involved in the design of leaf spring are the

laboring we have designed using pro-e wildfire4.0. The size and

dimensions of the leaf spring may be designed from the above table.

MODELING:

Modeling is a art of abstracting or representing phenomenon and

geometric modeling is no exception. A geometric model is defined as the

graphical information. Objects can be classified into three types from a

geometric construction point of view. These are two and half

dimensional, three dimensional or a combination of both. In this project,

the parts designed in the design module were transformed into solid

32

models through the principles of geometric modeling, by taking as a

reference using the software Pro/ENGINEER.

Why Pro/ENGINEER

Pro/ENGINEER is a powerful application. It is ideal for capturing

the design intent of our models because at its foundation is a practical

philosophy. Pro is a solid modeler. It develops models as solids allowing

to work in 3D environment.

In Pro-E

1. The solid models have volumes and surface areas.

2. We can calculate mass properties directly from the geometry we

create.

While we can manipulate a solid models display on the screen, the

model itself remains a solid.

GETTING STARTED:

The chapter introduces the various function of Pro/ENGINEER

user interface. In addition model, tree, viewing commands and file

management of Pro-E are discussed.

The Pro-E setup utility will automatically create a program group

with an icon. So accessing Pro-E becomes very easily.

33

COMMANDS FOR DESIGNING:-

Sketcher basic:

1.Line:

Line command allows to draw a line by specifying the

end points. We can right click on the sketcher window

to invoke line command.

Once the command is invoked, we can click at the

location, at which we want to start the line.

After clicking the start point a rubber band line

appears attached to the cursor. Now we can click at the

location where we want the line to end.

Parallel

Draws a line parallel to a selected linear entity. In this

option you have to select an existing entity for the

direction of the line and then pick the start points and

end points.

Perpendicular

Draws a line perpendicular to a selected linear entity.

Select an existing entity for the direction

(perpendicular) of the line and then pick the start points

and end points.

34

Tangent

This option facilitates to draw a line tangent from an

entity to the next point. The selected entity should be

an arc, ellipse, conic, and spline. It prompts for end

point, and then the line will be generated tangential to

those entities.

Horizontal

Using this option we can generate horizontal lines. The

end point of the line is taken as the start point of the

chained vertical line.

Vertical

Using this option we can generate vertical lines. The

end point of the line is taken as the start point of the

chained vertical line.

2.Arc-3- point / Tangent End:

3 point

Creates a 3-point arc by picking its end points and a points

on the circumference of the arc.

Tangent end

To create a tangent arc, pick an endpoint of an existing entity

to determine tangency, and then pick a location for the other

end point of the arc.

35

3.Arc concentric:

Creates a concentric arc. Select an arc to use its centre,

rubber band to the desired radius and sketch the arc.

4.Arc center/ Ends:

Creates an arc by picking its end points and a point on the

circumference of the arc.

Tangent

Creates an arc tangent to be selected three reference

entities.

Fillet

Creates an arc tangent to be selected two reference entities.

5. Trim-Delete segment:

When we use this command, we click and drag the cursor.

As we drag, sketcher creates a spline attached to the cursor.

Sketcher deletes any portion of any entity that intersects the

spline.

6.Trim-corner:

We can click any two entities on the portion of the entity that

we want to keep. Pro-E trims the two entities together.

Length

Using this option we can trim the entity to the specific

length. When we invoke this option Pro-E prompts for the

length value. After giving the length value it prompts to

36

select the entity to trim. Now the entity will be trimmed to

the specific length.

Fig.3:Sketchofleaf

37

Fig.4: Part of leaf

Fig5: Sketch of steel leaf

38

Fig6: Part of steel leaf

39

CHAPTER-5

ANALYSIS OF STRESS AND

DISPLACEMENT USING ANSYS

40

ANALYSIS OF STRESS AND DEFLECTION USING

ANSYS

Introduction

ANSYS is a general purpose finite element modeling package for

numerically solving a wide variety of mechanical problems. These

problems include: static/dynamic structural analysis (both linear and non-

linear), heat transfer and fluid problems, as well as acoustic and electro-

magnetic problems.

In general, a finite element solution may be broken into the

following three stages. This is a general guideline that can be used for

setting up any finite element analysis.

Preprocessing: defining the problem; the major steps in

preprocessing are given below:

Define key points/lines/areas/volumes

Define element type and material/geometric properties

Mesh lines/areas/volumes as required

The amount of detail required will depend on the dimensionality of

the analysis (i.e. 1D, 2D, axi-symmetric, 3D).

Solution: assigning loads, constraints and solving; here we specify

the loads (point or pressure), constraints (translational and rotational) and

finally solve the resulting set of equations.

41

Post processing: further processing and viewing of the results; in

this stage one may wish to see:

Lists of nodal displacements

Element forces and moments

Deflection plots

Stress contour diagrams

Finite Element Method using Pro/ENGINEER and ANSYS:

The transfer of a model from Pro/ENGINEER to ANSYS will be

demonstrated here for a simple solid model. Model idealizations such as

shells and beams will not be treated. Also, many modeling options for

constraints, loads, mesh control, analysis types will not be covered. These

are fairly easy to figure out once you know the general procedures

presented here.

Step 1. Make the part

Use Pro/E to make the part. Things to note are: be aware of your

model units note the orientation of the model (default coordinate system

in ANSYS will be the same as in Pro/E)

IMPORTANT: remove all unnecessary and/or cosmetic features like

rounds, chamfers, holes, etc., by suppressing them in Pro/E. Too much

small geometry will cause the mesh generator to create a very fine mesh

with many elements which will greatly increase your solver time. Of

course, if the feature is critical to your design, you will want to leave it.

You must compromise between accuracy and available CPU resources.

42

Fig7: ProE Model

The figure above shows the original model for this demonstration.

This is a model of a short cantilevered bracket that bolts to the wall via

the thick plate on the left end. Model units are inches. A load is applied at

the hole in the right end. Some cosmetic features are located on the top

surface and the two sides. Several edges are rounded. For this model, the

interest is in the stress distribution around the vertical slot. So, the plate

and the loading hole are removed, as are the cosmetic features and rounds

resulting in the "de-featured" geometry shown below. The model will be

constrained on the left face and a uniform load will be applied to the right

face.

43

Fig.8: FEA Model

Step 2. Create the FEA model

In the pull-down menu at the top of the Pro/E window, select

Applications > Mechanica

An information window opens up to remind you about the units

you are using. Press Continue

In the MECHANICA menu at the right, check the box beside FEM

Mode and select the command Structure.

A new toolbar appears on the right of the screen that contains icons

for creating all the common modeling entities (constraints, loads,

idealizations). All these commands are also available using the command

44

windows that will open on the right side of the screen or in dialog

windows that will open when appropriate.

Notice that a small green coordinate system WCS has appeared.

This is how you will specify the directions of constraints and forces.

Other coordinate systems (e.g. cylindrical) can be created as required and

used for the same purpose.

The MEC STRUCT menu appears on the right. Basically, to define

the model we proceed down this menu in a top-down manner. Model is

already selected for you which opens the STRC MODEL menu. This is

where we specify modeling information. We proceed in a top-down

manner. The Features command allows you to create additional

simulation features like datum points, curves, surface regions, and so on.

Idealizations let you create special modeling entities like shells and

beams. The Current CSYS command lets you create or select an alternate

coordinate system for specifying directions of constraints and loads.

Defining Constraints

For our simple model, all we need are constraints, loads, and a

specified material. Select Constraints > New

We can specify constraints on four entity types (basically points,

edges, and surfaces). Constraints are organized into constraint sets. Each

constraint set has a unique name (default of the first one is

ConstraintSet1) and can contain any number of individual constraints of

different types. Each individual constraint also has a unique name

(default of the first one is Constraint1). In the final computed model, only

one set can be included, but this can contain numerous individual

constraints.

45

Select Surface. We are going to fully constrain the left face of the

cantilever. A dialog window opens as shown above. Here you can give a

name to the constraint and identify which constraint set it belongs to.

Since we elected to create a surface constraint, we now select the surface

we want constrained (push the Surface selection button in the window

and then click on the desired surface of the model). The constraints to be

applied are selected using the buttons at the bottom of the window. In

general we specify constraints on translation and rotation for any mesh

node that will appear on the selected entity. For each direction X, Y, and

Z, we can select one of the four buttons (Free, Fixed, Prescribed, and

Function of Coordinates). For our solid model, the rotation constraints are

irrelevant (since nodes of solid elements do not have this degree of

freedom anyway). For beams and shells, rotational constraints are active

if specified.

46

For our model, leave all the translation constraints as FIXED, and

select the OK button. You should now see some orange symbols on the

left face of the model, along with some text labels that summarize the

constraint settings.

Defining Loads

In the STRC MODEL menu select Loads > New > Surface. The

FORCE/MOMENT window opens as shown above. Loads are also

organized into named load sets. A load set can contain any number of

individual loads of different types. A FEM model can contain any number

of different load sets. For example, in the analysis of a pressurized tank

on a support system with a number of nozzle connections to other pipes,

one load set might contain only the internal pressure, another might

contain the support forces, another a temperature load, and more might

contain the forces applied at each nozzle location. These can be solved at

the same time, and the principle of superposition used to combine them in

numerous ways. Create a load called "end load" in the default load set

(LoadSet1)

Click on the Surfaces button, and then select the right face of the

model and middle click to return to this dialog. Leave the defaults for the

load distribution. Enter the force components at the bottom. Note these

are relative to the WCS. Then select OK. The load should be displayed

symbolically as shown in the figure below.

47

Fig.9: FEA load set

Note that constraint and load sets appear in the model tree. You can

select and edit these in the usual way using the right mouse button.

Assigning Materials

Our last job to define the model is to specify the part material. In

the STRC MODEL menu, select Materials > Whole Part

In the library dialog window, select a material and move it to the

right pane using the triple arrow button in the center of the window. In an

assembly, you could now assign this material to individual parts. If you

select the Edit button, you will see the properties of the chosen material.

At this point, our model has the necessary information for solution

(constraints, loads, material).

48

Step 3. Define the analysis

Select Analyses > New

Specify a name for the analysis, like "ansys test". Select the type

(Structural or Modal). Enter a short description. Now select the Add

buttons beside the Constraints and Loads panes to add ConstraintSet1 and

LoadSet1 to the analysis. Now select OK.

Step 4. Creating the mesh

We are going to use defaults for all operations here. The MEC

STRUCT window, select Mesh > Create > Solid > Start

Accept the default for the global minimum. The mesh is created

and another dialog window opens (Element Quality Checks).This

indicates some aspects of mesh quality that may be specified and then, by

selecting the Check button at the bottom, evaluated for the model. The

results are indicated in columns on the right. If the mesh does not pass

these quality checks, you may want to go back to specify mesh controls

(discussed below). Select Close. Here is an image of the default mesh,

shown in wire frame.

49

Fig.10: FEA Mesh

Improving the Mesh

In the mesh command, you can select the Controls option. This will

allow you to select points, edges, and surfaces where you want to specify

mesh geometry such as hard points, maximum mesh size, and so on.

Beware that excessively tight mesh controls can result in meshes with

many elements.

For example, setting a maximum mesh size along the curved ends

of the slot results in the following mesh. Notice the better representation

of the curved edges than in the previous figure. This is at the expense of

more than double the number of elements. Note that mesh controls are

also added to the model tree.

50

Step 5. Creating the Output file

All necessary aspects of the model are now created (constraints,

loads, materials, mesh). In the MEC STRUCT menu, select Run

This opens the Run FEM Analysis dialog window shown here. In

the Solver pull-down list at the top, select ANSYS. In the Analysis list,

select Structural. You pick either Linear or Parabolic elements. The

analysis we defined (containing constraints, loads, mesh, and material) is

listed. Select the Output to File radio button at the bottom and specify the

output file name (default is the analysis name with extension .ans). Select

OK and read the message window. We are now finished with Pro/E. Go

to the top pull-down menus and select Applications > Standard Save the

model file and leave the program. Copy the .ans file from your Pro/E

working directory to the directory you will use for running ANSYS.

51

Step 6. Importing into ANSYS

Launch ANSYS Interactive and select File > Read Input From...

Select the .ans file you created previously. This will read in the entire

model. You can display the model using (in the pull down menus) Plot >

Elements.

Step 7. Running the ANSYS solver

In the ANSYS Main Menu on the left, select Solution > Solve >

Current LS > OK. After a few seconds, you will be informed that the

solution is complete.

Step 8. Viewing the results

There are myriad possibilities for viewing FEM results. A common

one is the following:

General Postprocessor > Plot Results > Contour Plot > Nodal Solution.

Pick the Von Mises stress values, and select Apply. You should

now have a color fringe plot of the Von Mises stress displayed on the

model.

52

Fig11: Stress distribution for steel leaf

Properties of steel leaf:

Properties Value

Tensile Strength 1962 N/mm2

Modulus of Elasticity 2.1*105 N/mm2

Poissons Ratio 0.2

53

Fig.12: Stress distribution for A-Glass Fiber leaf spring

Tab.1: Properties of A-Glass Fiber, Generic

Properties Value

Density 2.44 g/cc

Tensile Strength 3310 MPa

Modulus of Elasticity 68.9 GPa

Poissons Ratio 0.183

Shear Modulus 29.1 GPa

Specific Heat Capacity 0.796 J/g-C

54

Fig.13: Stress distribution for C-Glass Fiber leaf spring

Tab.2: Properties of C-Glass Fiber, Generic

Properties Value

Density 2.52 - 2.56 g/cc



Poissons Ratio 0.276


55

Fig.14: Stress distribution for D-Glass Fiber leaf spring

Tab.3: Properties of D-Glass Fiber, Generic

Properties Value

Density 2.11 g/cc



Poissons Ratio 0.2


56

Fig.15: Stress distribution for E-Glass Fiber leaf spring

Tab.4: Properties of E-Glass Fiber, Generic

Properties Value

Density 2.54 - 2.60 g/cc



Poissons Ratio 0.2


57

CHAPTER-6

GRAPH FOR STRESS AND

DEFLECTION

58

Tab.5: Comparison results of stresses

MATERIAL OF MONO COMPOSITE MAXIMUM STRESS

(MPa)

A-Glass Fiber, Generic 462.002

C-Glass Fiber, Generic 341.474

D-Glass Fiber, Generic 433.089

E-Glass Fiber, Generic 217.217

0

50

100

150

200

250

300

350

400

450

500

A-Glass C-Glass D-Glass E-Glass

STRESS Vs MATERIAL

stress in MPa

59

Tab.6: Comparison results of deflection

MATERIAL OF MONO COMPOSITE MAXIMUM

DEFLECTION (mm)

A-Glass Fiber, Generic 173.3

C-Glass Fiber, Generic 129.7

D-Glass Fiber, Generic 161.7

E-Glass Fiber, Generic 82.2

0

20

40

60

80

100

120

140

160

180

C-Glass D-Glass E-Glass

DEFLECTION Vs MATERIAL

173.3

60

CHAPTER-7

RESULTS

61

RESULTS:

Experimental results from testing the leaf springs under static

loading containing the stresses and deflection are listed in the Table.

These results are also compared with FEA in Table. Testing has been

done for unidirectional mono composite leaf spring only. Since the

composite leaf spring is able to withstand the static load, it is concluded

that there is no objection from strength point of view also, in the process

of replacing the conventional leaf spring by composite leaf spring. The

major disadvantages of composite leaf spring are chipping resistance. The

matrix material is likely to chip off when it is subjected to a poor road

environments (that is, if some stone hit the composite leaf spring then it

may produce chipping) which may break some fibers in the lower portion

of the spring. This may result in a loss of capability to share flexural

stiffness. But this depends on the condition of the road. In normal road

condition, this type of problem will not be there. Composite leaf springs

made of polymer matrix composites have high strength retention on

ageing at severe environments. The steel leaf spring was replaced with an

composite one. The objective was to obtain a spring with minimum

weight which is capable of carrying given static external forces by

constraints limiting stresses and displacements. The weight of the leaf

spring is reduced. Thus, the objective of the unsprung mass is achieved to

a larger extent. The stresses in the composite leaf spring are much lower

than that of the steel spring.

62

Tab.7: Comparison results of load, deflection and stresses:

Material

Static load

(N)

Maximum

deflection

(mm)

Maximum

stress (MPa)

Steel 4000 210.2 534.02

Fiber Generic

A-Glass

4000 173.3 462.002

Fiber Generic

C-Glass

4000 129.7 341.474

Fiber Generic

D-Glass

4000 161.7 433.089

Fiber Generic

E-Glass

4000 82.2 217.217

63

CHAPTER-8

ADVANTAGES OF MONO COMPOSITE

LEAF SPRING

64

ADVANTAGES:

1. To prevent the road shocks from being transmitted to the

vehicles components.

2. To preserve the stability of the vehicles in pitching or

rolling, while in motion.

3. The weight of the mono composite leaf spring is low.

4. The mono composite leaf spring deflection and stress is

high.

5. The noise will be reduced in this leaf spring.

6. No corrosive resistance of this leaf spring.

7. The mono composite leaf spring flexibility is higher than

the steel.

8. The life of the material is more than the steel.

9. The high efficiency of the leaf spring.

65

CHAPTER-9

CONCLUSION

66

CONCLUDING REMARKS:

The development of a composite mono leaf spring having constant

cross sectional area, where the stress level at any station in the leaf

spring is considered constant due to the parabolic type of the

thickness of the spring, has proved to be very effective.

The study demonstrated that composites can be used for leaf

springs for light weight vehicles and meet the requirements,

together with substantial weight savings.

The 3-D modeling of both steel and composite leaf spring is done

and analyzed using ANSYS.

A comparative study has been made between composite and steel

leaf spring with respect to weight, cost and strength.

The analytical results were compared with FEA and the results

show good agreement with test results.

From the results, it is observed that the composite leaf spring is

lighter and more economical than the conventional steel spring

with similar design specifications.

Adhesively bonded end joints enhance the performance of

composite leaf spring for delamination and stress concentration at

the end in compare with bolted joints.

67

.

CHAPTER-10

BIBLIOGRAPHY

68

REFERENCES:

1. Rajendran, I., Vijayarangan, S. Design and Analysis of a

Composite Leaf Spring Journal of Institute of Engineers India 82

2002: pp. 180 187..

2. Dharam, C. K. Composite Materials Design and Processes for

Automotive Applications. The ASME Winter Annual Meeting, San

Francisco, December 10-15, 1978.

3. Vijayarangan, S., Ganesan, N. Static Stress Analysis of a

Composite Bevel Gear using a Three-dimensional Finite Element

Method Computer Structures 51 (6) 1994.

4. Tanabe, K., Seino, T., Kajio, Y. Characteristics of Carbon/Glass

Fiber Reinforced Plastic Leaf Spring,.

5. Jones, R. M. Mechanics of Composite Materials. 2e, Mc Graw-

Hill Book Company, 1990.

6. ANSYS Inc: ANSYS Users Manual, Rev. 1995, 5.2-Vol. I

Houston, PA.

WEB ADDRESS:

www.matweb.com.

www.wikipedia.org.

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