Presented By
MANISH AGRWAL

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COMPOSITES & MECHANISM
Introduction
 Composite materials have been used throughout history
– ancient building material
– straw/mud huts still used today
 The human body relies on a natural composite
– bone
– hard brittle hydroxyapatite and soft protein collagen
 Wood is also a natural composite
– strong and flexible cellulose fibres are surrounded by lignin matrix
 The use of modern composites allows us toproduce materials with unusual combinations of properties that cannot be met by conventional materials
Composite materials have been especially useful in aerospace, underwater and transport applications
This is because composite structural materials have
– low densities
– high stiffness
– can be abrasion and impact resistant
– and are not easily corroded
What Is A Composite?
In general it is a structural material made of two or more different materials.
Definition:
Any combination of two or more different materials at the macroscopic level.
OR
Two inherently different materials that when combined together produce a material with properties that exceed the constituent materials.
Classification
Types of Composite Materials
There are five basic types of composite materials: Fiber, particle, flake, laminar or layered and filled composites.
Fiber Composites
 In fiber composites, the fibers reinforce along the line of their length. Reinforcement may be mainly 1-D, 2-D or 3-D. Figure shows the three basic types of fiber orientation.
Particle Composites
 Particles usually reinforce a composite equally in all directions (called isotropic). Plastics, cermets and metals are examples of particles.
 Particles used to strengthen a matrix do not do so in the same way as fibers. For one thing, particles are not directional like fibers. Spread at random through out a matrix, particles tend to reinforce in all directions equally.
Flake Composites
Flakes, because of their shape, usually reinforce in 2-D. Two common flake materials are glass and mica. (Also aluminum is used as metal flakes)
Laminar Composites
 Laminar composites involve two or more layers of the same or different materials. The layers can be arranged in different directions to give strength where needed. Speedboat hulls are among the very many products of this kind.
 In laminar composites outer metal is not called a matrix but a face. The inner metal, even if stronger, is not called a reinforcement. It is called a base.
 We can divide laminar composites into three basic types
Unreinforced–layer composites
1. All–Metal
2. Metal–Nonmetal
3. Nonmetal
Reinforced–layer composites
Combined composites
 A lamina (laminae) is any arrangement of unidirectional or woven fibers in a matrix. Usually this arrangement is flat, although it may be curved, as in a shell.
 A laminate is a stack of lamina arranged with their main reinforcement in at least two different directions.
Filled Composites
There are two types of filled composites.
 In one, filler materials are added to a normal composite result in strengthening the composite and reducing weight.
 The second type of filled composite consists of a skeletal 3-D matrix holding a second material. The most widely used composites of this kind are sandwich structures and honeycombs.
Combined Composites
It is possible to combine several different materials into a single composite. It is also possible to combine several different composites into a single product. A good example is a modern ski. (combination of wood as natural fiber, and layers as laminar composites)
Benefits of Composites
 Cost:
Prototypes
Mass production
Part consolidation
Maintenance
Long term durability
Production time
Maturity of technology
 Weight:
Light weight
Weight distribution
 Strength and Stiffness:
High strength-to-weight ratio
Directional strength and/or stiffness
 Dimension:
Large parts
Special geometry
 Surface Properties:
Corrosion resistance
Weather resistance
Tailored surface finish
 Thermal Properties:
Low thermal conductivity
Low coefficient of thermal expansion
 Electric Property:
High dielectric strength
Non-magnetic
Radar transparency
 The Structure of Composites
Consist of two distinct phases
– matrix and a reinforcing phase
Matrices can be
– metals (Al, Ti)
– ceramics (Al2O3, ZrO2)
– polymers (epoxy, polyester, phenolic)
Reinforcing phases can have different shapes
– fibres, whiskers, particulates
Technologically, fibre composites most important
– glass, carbon, Spectra (PE), Kevlar (aramid)
Fibre composites
 Usually combinations of ceramic, polymer or glass fibres in a polymer matrix
 Typically 40-60 % fibre by volume
 Utilize the very good properties of the fibres
 Fibre composites have a good combination of stiffness, density and fracture toughness
 However they are often expensive
 They may be difficult to process
 Often difficult to detect damage (cracks)
Properties of Fibres
 High strength of materials can be achieved due to low probability of flaws in individual fibres
 Polymers may be oriented into fibres (Spectra or Kevlar) to utilize the strong C – C bonds of polymer backbone
 For carbon fibres, graphite plate structure can be oriented to take advantage of strong bonding
Properties of Matrix
 The matrix binds the fibres together and protects them from external damage
 It transmits external loads to the fibres
– the matrix itself usually carries only a small fraction of the load
 It separates the fibres and stops cracks from propagating directly from fibre to fibre
 It supports the fibres laterally under compression loading
 It is usually has a low density to produce a composite with a low density
 It is advantageous if the matrix has some ductility
– reinforcing phase often very stiff
 Deformation of Aligned Long Fibre Composites
 Long fibre composite materials are highly anisotropic
 Let’s look at two extreme cases