Fabrication of Composite Leaf Spring

-By

Pratik Shriraj Gandhi

T.Y.B.Tech

Production (Sandwich)

111213021

1. Introduction

• Suspension

• Conservation of natural resources and economize

energy, weight reduction

• Load carrying capacity

• Steel springs makes vehicles heavy

• Key factors in selecting material- shock absorbing &

load

• Functions - locating points of stress,

damping vibrations and springing

• Absorb & store energy

• Specific strain energy -

• Weight reduction with equal stability, high specific

strength & high specific Modulus

• Alternative - Glass Fiber Reinforced Plastic (GFRP)

• Problems faced - weight increase, low performance,

excess wear

• Composites - lightweight, strong, high strength to

weight ratio

2. Conventional Leaf Springs

• Absorbs sudden load and

fluctuations

• Accumulates elastic energy

• Provide suspension for

chassis of vehicle

2.1. Working of Leaf Springs

• Semi-elliptic leaf springs

• Blades vary in length, given initial curvature or

cambered tend to straighten under load

• Lengthiest blade - Master leaf

• Other blades - Graduated leaves

• Front end connected with pin

joint, rear end with shackle

• Vehicle across projection on

road, wheel moves up,

deflecting the spring which

changes the length between

the spring eyes

2.2. Types

Leaf springs

Multi-Leaf Spring

Mono Leaf Spring Parabolic Single

Leaf Spring

Fiberglass Leaf Spring

•more than 1

leaf

•assembled

using center

bolt and clips

•only 1 leaf

•constant width

and thickness

•lighter spring

rate

•one main leaf

with tapered

thickness

•lighter than multi-

leaf springs

•made of a

mixture of plastic

fibers and resin

•sensitive to heat

•lighter than all

other springs but

cost is three times

greater

3.Design Parameters

• Material selected

• Tensile strength

• Yield strength

• Young’s modulus E

• Design stress (σb)

• Total length

• Spring weight

• Arc length between

axle seat and Front eye

• Arc height at axle seat

• Spring rate

• Normal static loading

• Available space for

spring width

4. Problems with Conventional Leaf

Springs

• Research about wt. reduction with

stable design of vehicle

• Steel leaf springs make it heavy and

affects performance

• Vertical forces on spring eye causes

early failure

• Depletion of natural resources from

mines

• Development in composites give

properties needed for suspension

5.Composite Materials

• Definition - Structural material with two or more

combined constituents at macroscopic level & not

soluble in each other

Reinforcing Phase forms-

Fibers , particles , flakes

Matrix Phase- Continuous Materials

E.g.-

concrete reinforced with steel

epoxy reinforced with Graphite fibers

reinforced phase

Matrix phase

Composite

5.1. Classification

Composites

Matrix Based

Polymer Matrix

Metal Matrix

Ceramic Matrix

Reinforcement Based

Fiber Reinforced

Whisker Reinforced

Particle Reinforced

6. Fabrication Techniques

• Different loading, various materials &

Application feasibility

• Constant cross section design, hand lay-up

process is used to study

• Unidirectional GFRP material

Constant thickness, constant width design

Constant thickness, varying width design

Varying width, varying thickness design

7. Hand Lay-Up Process

• Reinforcement & painting

with matrix resin layer by

layer

• Template(Mould die)

• Releasing agent(gel/wax) for

surface finish

• Uniform application, roller to

remove trapped air

• Duration-30 mins

• Mould allowed to cure for 4-5

days at room temperature

7.1. Sheet Preparation

• Template - Aluminium Frame

• Wt of glass-fiber sheet 150 gms

• Epoxy resin with Hardener(9:1)

• Releasing agent - Silicon gel

• Repeat process till desired

thickness is obtained

• After curing, sheet pulled out

Cut in design dimensions

• Sometimes Heat is used for

proper setting of fiber layers

8. Experimental Tests• 1.Flexural Test

Rectangular cross section bar

deflected at constant rate

3 point bending, load at center

Universal Testing Machine-

3 point Flexural fixture

• 2. Tensile Test

Force needed by composite till

breaking point

Extensometer or Strain Gauge

Elongation , Tensile Modulus &

Stress-Strain Diagram

• 3. Impact Test

Force for breaking under

high speed tensile load

Pendulum strike on anvil

at specimen

Impact energy using TMI

Impact Tester

9. Advantages & Disadvantages

Advantages

• Lightweight, extremely

strong

• Weigh ¼ th for same

strength

• Corrosion & chemical

Resistance

• Excellent elastic properties

• Regains shape after

bending till certain limit ,

useful for spring

applications

Disadvantages

• High cost of fabrication ,

complicated time

consuming process

• Repair procedure is

complex

• Unpredictable mechanical

characterization

• Not isotropic , need more

parameters for evaluation

• Compressive strength not

dependable

10. Discussion & Conclusion Stress developed found well within limits with

good factor of safety

Longitudinal orientation of fibers in laminate offers strength

Deflection is less compared to steel for same loading

condition

Bending stress lowered

Conventional leaf springs 3.5 times heavier than Composite

springs

Material saving achieved

Lighter and economical for use but sensitive to heat

cycles

Sometimes heat treated for more stiffness

High strength retention at severe environments

Good alternative for steel in suspension applications

In future, experimental verification for Bending, Torsion

and Hardness to be done

Cost reduction and optimum fabrication process

development for mass production