35331802-introduction-and-classification-of-composites.ppt

ME 1014 Composite Materials

Prof.V.Alfred Franklin., St.Xavier’s Catholic College of Engineering Nagercoil, India.

Composite Material ? Two inherently different materials that when combined together produce a material with properties that exceed the constituent materials. Any combination of two or more different materials at the macroscopic level..

The constituents retain their identities, i.e.., they do not dissolve or merge into each other, although they act in concert. Composites: Artificially produced multiphase materials.

Composite Material ? 

Composites: A judicious combination of two or more materials that produces a synergistic effect. A material system composed of two or more physically distinct phases whose combination produces aggregate properties that are different from those of its constituents.

Phases of Composites Matrix Phase: continuous phase, surrounds other phase (e.g.: metal (Cu, Al, Ti, Ni…); , ceramic (SiC…), or polymer (Thermosets, thermoplastics, Elastomers) Reinforcement Phase: dispersed phase, discontinuous phase (e.g.: Fibers, Particles, or Flakes) 􀂃

→ Interface between matrix and reinforcement

Interfacial properties - the interface may be regarded as a third phase.

Examples: – Straw in mud – Wood (cellulose fibers in hemicellulose and lignin) – Bones (soft protein collagen and hard apatite minerals) – Pearlite (ferrite and cementite)

Micro mechanics/ Macro mechanics?

Major Constituents Fiber Matrix Fillers Coupling agents Colorants

FIBERS Principle Load carrying member Main constituent and they occupy largest volume fraction Diameter of a single fiber is about 10 microns They may be continuous or discontinuous in length.

TYPES OF GLASS FIBER  

E-Glass – E stands for electrical S-Glass – S stands for high silica content  

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C-Glass – C stands for Corrosion  

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Low dielectric constants

A-Glass – A Stands for appearance 

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Structural applications

D-Glass – D stands for Dielectric 

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Used in Chemical applications Storage tanks

R-Glass – R stands for Rigid 

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High thermal expansion coefficient High fatigue strength

To improve surface appearance For ornamental works

E-CR Glass – E-CR stands for Electrical and corrosion resistance AR Glass – AR stands for Alkali resistance

• Critical fiber length for effective stiffening & strengthening:

fiber strength in tension

f d fiber length  15 c

fiber diameter

shear strength of fiber-matrix interface

Efficiency : fiber length Shorter, thicker fiber:

 d fiber length  15 f c

Poorer fiber efficiency

Longer, thinner fiber:

 d fiber length  15 f c

Better fiber efficiency

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Why are Fibers of a Thin Diameter? 1. Thinner fiber has higher ultimate strength because less chance for inherent flaws. Similar phenomenon in metals and alloys (Strength of a thin wire can be higher than its bulk material). 2. For the same volume of fibers, thinner fibers has larger surface area thus has stronger bond with matrix. (The total surface area of fibers is inversely proportional to the diameter of fibers) 3. Thinner fiber has larger flexibility ( 1/(EI)) and therefore is able to be bent without breaking (Woven fabric performs can be made before impregnated with polymer matrix).

Composite Strength: Longitudinal Loading Continuous fibers - Estimate fiber-reinforced composite strength for long continuous fibers in a matrix

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Longitudinal deformation

c = mVm + fVf volume fraction

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Ec = Em Vm + EfVf

Ff E f Vf  Fm E mVm

but

c = m = f isostrain

longitudinal (extensional) modulus f = fiber m = matrix C-composite

Remembering: E = / and note, this model corresponds to the “upper bound” for particulate composites

Matrix / Resins -

The resin or polymer is the “glue” that holds

the composite together -The primary functions of the resin are to transfer stress between the reinforcing fibers. Examples: Polyester, Epoxy, Vinyl Ester, Polyurethane

Role of Matrices in Composites   

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Transfer stresses between the fibers. Provide a barrier against an adverse environment. Protect the surface of the fibers from mechanical abrasion. Determine inter-laminar shear strength. Determine damage tolerance of composites. Determine in-plane shear strength. Determine the processibility of composites. Determine heat resistance of composites.

Role of Matrix The primary roles of the matrix alloy then are to provide efficient transfer of load to the fibers and to blunt cracks in the event that fiber failure occurs and so the matrix alloy for continuously reinforced composites may be chosen more for toughness than for strength. 

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On this basis, lower strength, more ductile, and tougher matrix alloys may be utilized in continuously reinforced composites. For discontinuously reinforced composites, the matrix may govern composite strength. -Then, the choice of matrix will be influenced by consideration of the required composite strength and higher strength matrix alloys may be required.

Functions of Matrix  

Holds the fibres together. Protects the fibres from environment.

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Distributes the loads evenly between fibres so that all fibres are subjected to the same amount of strain.

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Enhances transverse properties of a laminate. Improves impact and fracture resistance of a component.

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Helps to avoid propagation of crack growth through the fibres by providing alternate failure path along the interface between the fibres and the matrix.

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Carry inter-laminar shear.

Desired Properties of a Matrix 

Reduced moisture absorption.

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Low shrinkage.

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Low coefficient of thermal expansion.

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Good flow characteristics so that it penetrates the fibre bundles completely and eliminates voids during the compacting/curing process. Must be elastic to transfer load to fibres.

Desired Properties of a Matrix 

Reasonable strength, modulus and elongation (elongationshould be greater than fibre).

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Strength at elevated temperature (depending on application).

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Low temperature capability (depending on application).

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Excellent chemical resistance (depending on application).

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Should be easily processable into the final composite shape.

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Dimensional stability (maintains its shape).

FILLERS      

Control Composites’ Cost Improved Mechanical Properties Improved Chemical Properties Reduced Creep & Shrinkage Low Tensile Strength Fire Retardant & Chemical Resistant

TYPES OF FILLER      

Calcium Carbonate Kaolin Alumina Trihydrate Mica Feldspar Wollastonite Silica, Talc, Glass

ADDITIVES    

Improved Material Properties Aesthetics Enhanced Workability Improved Performance

ADDITIVE TYPES       

Catalysts Promoters Inhibitors Coloring Dyes Releasing Agents Antistatic Agents Foaming Agents

Composites Offer High

Strength to weight ratio High Stiffness to weight ratio High Modulus to weight ratio Light Weight Directional strength Corrosion resistance Weather resistance Dimensional stability -low thermal conductivity -low coefficient of thermal expansion Radar transparency Non-magnetic High impact strength High dielectric strength (insulator) Low maintenance Long term durability Part consolidation Small to large part geometry possible Tailored surface finish Design Flexibility

Property comparison Material

Tensile modulus (E) ( GN / m 2 )

Tensile strength(  u ) ( GN / m 2 )

E-Glass

72.4

3.5

Graphite

390.0

Boron

Density ( ) ( g / cm 3 )

Specific modulus (E/ )

Specific strength ( u /  )

2.54

28.5

1.38

2.1

1.90

205.0

1.1

385.0

2.8

2.63

146.0

1.1

Kevlar – 49

130

2.8

1.50

87

Steel

210

0.34 – 2.1

7.8

26.9

1.87 0.043 – 0.27

Aluminum alloys

70

0.14 – 0.62

2.7

25.9

0.052 – 0.23

Composite strength depends on the following factors: 

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Inherent fiber strength, Fiber length, Number of flaws Fiber shape The bonding of the fiber (equally stress distribution) Voids Moisture (coupling agents)

Classification of Composite Materials 1.

Traditional composites – composite materials that

occur in nature or have been produced by civilizations for many years  Examples: wood (cellulose fibers in lignin matrix), concrete, asphalt 2.

Synthetic composites - modern material systems normally associated with the manufacturing industries, in which the components are first produced separately and then combined in a controlled way to achieve the desired structure, properties, and part geometry

Classification of Synthetic Composites: Based on Matrix Metal

Ceramic

Polymer

Metal

Powder metallurgy parts – combining immiscible metals

Cermets (ceramic-metal composite)

Brake pads

Ceramic

Cermets, TiC, TiCN Cemented carbides – used in tools Fiber-reinforced metals

SiC reinforced Al2O3 Tool materials

Fiberglass

Matrix Reinforcement

Kevlar fibers in an epoxy matrix

Polymer Elemental (Carbon, Boron, etc.)

Fiber reinforced metals Auto parts aerospace

Rubber with carbon (tires) Boron, Carbon reinforced plastics

MMC’s

CMC’s

PMC’s

Metal Matrix Composites

Ceramic Matrix Comp’s.

Polymer Matrix Comp’s

Classification of Synthetic Composites : Based on reinforcements There are five basic types of composite materials: Fiber, particle, flake, laminar or layered and filled composites.

1. 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. 

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1-D gives maximum strength in one direction. 2-D gives strength in two directions.

Isotropic gives strength equally in all directions.

2. 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.  Cermets (1) Oxide–Based cermets (e.g. Combination of Al2O3 with Cr) (2) Carbide–Based Cermets (e.g. Tungsten–carbide, titanium–carbide)  Metal–plastic particle composites (e.g. Aluminum, iron & steel, copper particles)  Metal–in–metal Particle Composites and Dispersion Hardened Alloys (e.g. Ceramic–oxide particles) 

3. 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)

Flake Composites

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1. 2. 3.

A flake composite consists of thin, flat flakes held together by a binder or placed in a matrix. Almost all flake composite matrixes are plastic resins. The most important flake materials are: Aluminum Mica Glass

Flake Composites

Basically, flakes will provide:  Uniform mechanical properties in the plane of the flakes  Higher strength  Higher flexural modulus  Higher dielectric strength and heat resistance  Better resistance to penetration by liquids and vapor  Lower cost

4. Laminar Composites 

Laminar Composites are composed of layers of materials held together by matrix.

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.

Laminar Composites

We can divide laminar composites into three basic types:  Unreinforced–layer composites (1) All–Metal (a) Plated and coated metals (electrogalvanized steel – steel plated with zinc) (b) Clad metals (aluminum–clad, copper–clad) (c) Multilayer metal laminates (tungsten, beryllium) (2) Metal–Nonmetal (metal with plastic, rubber, etc.) (3) Nonmetal (glass–plastic laminates, etc.) 

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Reinforced–layer composites (laminae and laminates) Combined composites (reinforced–plastic laminates well bonded with steel, aluminum, copper, rubber, gold, etc.)

Laminar Composites

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Like all composites laminar composites aim at combining constituents to produce properties that neither constituent alone would have. In laminar composites (Un reinforced) 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.

Laminar Composites

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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 different directions.

Laminate Sequence

5. 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.

Sandwich Structure – Foam Core Consists of a relatively thick core of low density foam bonded on both faces to thin sheets of a different material

Figure 9.7 - Laminar composite structures: (b) sandwich structure using foam core

Sandwich Structure – Honeycomb Core  An alternative to foam core  Either foam or honeycomb achieves high strength-to-weight and stiffness-to-weight ratios

Figure 9.7 - Laminar composite structures: (c) sandwich structure using honeycomb core

6.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)