design of leaf spring using composite material and its fabrication method

1. Fabrication of Composite Leaf Spring
-By
Pratik Shriraj Gandhi
T.Y.B.Tech
Production (Sandwich)
111213021

2. 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

3. • 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

4. 2. Conventional Leaf Springs
• Absorbs sudden load and
fluctuations
• Accumulates elastic energy
• Provide suspension for
chassis of vehicle

5. 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

6. 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

7. 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

8. 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

9. 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

10. 5.1. Classification
Composites
Matrix Based
Polymer
Matrix
Metal
Matrix
Ceramic
Matrix
Reinforcement
Based
Fiber
Reinforced
Whisker
Reinforced
Particle
Reinforced

11. 6. Fabrication Techniques
• Different loading, various materials &
Application feasibility
Constant thickness, constant width design
Constant thickness, varying width design
Varying width, varying thickness design
• Constant cross section design, hand lay-up
process is used to study
• Unidirectional GFRP material

12. 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

13. 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

14. 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

15. 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

16. 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

17.  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