CHAPTER 1:

INTRODUCTION Instructor: Phan Thi Thu Ha, MSc.

Thai Nguyen University of Technology

Overview

• Definition

• Characteristics

• Classification

- Particle-reinforced composites

- Fiber-reinforced composites

+ Matrix

+ Fibers

- Structural composites

• Some common types of composites:

- Polymer matrix composites

- Metal matrix composites

- Ceramic matrix composites

- Carbon-carbon composites

• Manufacturing techniques

• Applications

Definition

What is a composite?

• A composite material is made by combining 2 or more

distinct materials to give an unique and better

combination of properties.

• Distinct materials:

- Different at the molecular level (chemically

dissimilar) and mechanically separable.

- In bulk form, the constituent materials work

together but remain in their original forms (separated by a

distinct interface)

• Constituents: Matrix and reinforcing phase

Composite Characteristics

Advantages:

• Low density

• High specific stiffness (stiffness-to-density ratio)

• Very high specific strength (strength-to-density ratio).

• Much higher fatigue strength

• High corrosion resistance

• Design flexibility

• Good impact properties

• Noise, vibration, and harshness characteristics are better for

CM than metals

• Data adapted from Marllick

Disadvantages:

• Materials cost

• Manufacturing suitable for high production rates

• Lack of database

• Low temperature resistance

• Low resistance to solvents, environmental stress cracking

• Absorb moisture

Classification of composite types

Large-

particle

Dispersion-

strengthened

Particle-reinforced

Continuous

(aligned)

Aligned Randomly

oriented

Discontinuous

(short)

Fiber-reinforced

Laminates Sandwich

panels

Structural

Composites

Particle-reinforced composites

• Large-particle composites

- Concrete

• Dispersion-strengthened composites

Fiber-reinforced composites

• Are the most important composites

• Design goals:

- Low density;

- High specific strength;

- High specific modulus.

• Constituents: - Fibers and matrix

- Agents, coatings.

Fibers • Characteristics:

- Principal constituents;

- Occupy the largest volume fraction;

- Share the major portion of the load acting.

• Design considerations:

- fiber type, fiber volume fraction, fiber length, fiber

orientation.

• Some common fiber types:

- Glass fiber, carbon fiber, aramid fiber, boron fiber,

ceramic fiber, etc.

• Tensile stress-strain for reinforcing fibers:

Matrix

• Roles:

- Keep fibers in place;

- Transfer stress between fibers;

- Provide a barrier against an adverse environment

(chemicals, moisture)

- Protect the surface of fibers (by abrasion)

- Minor role in the tensile load-carrying capacity, but major

influence on the compressive, inter-laminar shear, in-

plane shear, buckling, etc.

• Types of matrix:

- Polymer matrix, metal matrix, ceramic matrix

Polymer matrix • Thermoset vs Thermoplastic

• Thermoset (resins):

- Examples: epoxy, polyester, and vinyl ester

- Used as matrix in continuous or long fiber-reinforced

composites

- Molecules are joined by cross-links rigid, 3-D network

structure. Once cross-links are formed, it cannot be melted

by heat.

- Long fabrication time.

(curing)

• Thermal plastics:

- Examples: PVC, PS, PP

- Individual molecules are not chemically joined together;

- Held in place by Van der Waals bonds and hydrogen bonds

that can be broken by heat;

- Heat-softened, melted, and reshaped as many times as

desired.

Polymer-matrix Composites (PMC)

Matrix: Polymer resin

Reinforcement: Fibers

• Glass fiber-reinforced polymer composites

• Carbon fiber-reinforced polymer composites

• Aramid fiber-reinforced polymer composites

Glass fiber-reinforced polymer composites

• Glass is popular as a fiber reinforcement because:

- Easily drawn into high-strength fibers;

- Relatively strong very high specific strength composites

- Inertness with various plastics

- E-glass, C-glass, S-glass

• High strength but not very stiff and rigid enough for some applications such as: structure members for airplanes and bridges

• Limited to services temperatures, below 200C ( t polyimide resins)

• Applications: automotive and marine bodies, storage containers, industrial flooring, etc.

Carbon fiber-reinforced polymer composites

• Carbon characteristics:

- Very high specific moduli and specific strengths (207-

1035 Gpa);

- Retain characteristics at elevated temperatures, high-

temperature oxidation;

- Not affected by moisture, inert with variety of solvents

Metal-matrix composites

• Matrix:

- Ductile material (alloys of Al, Ti, Mg, Cu, etc.)

• Reinforcement:

- Continuous fiber: carbon, silicon carbide (SiC), boron,

Al2O3

- Discontinuous reinforcement: SiC whiskers, chopped fibers

of Al2O3

- Particulates: SiC, Al2O3

• Advantages:

- Higher operating temperatures;

- No flammability;

- Greater resistance

Disadvantages:

- Much more expensive than PMC

- Reactions between matrix and reinforcement at elevated

temperatures composite degradation surface coating

or modifying the matrix alloy composition.

• Applications:

- Aerospace industry: Aluminum-alloy metal matrix

composites

Ceramic-matrix composites Particulates, fibers or whiskers of one ceramic are

embedded into a matrix of another ceramic.

Improve significantly fracture toughness

Fracture toughness is the ability of a material

containing a crack to resist fracture.

• Applications:

- In high-temperature and severe-stress applications :

Components in automobile and aircraft gas turbine engine

Carbon-Carbon composites

• Carbon fiber-reinforced carbon-matrix composites

• Advantages:

- High tensile moduli and tensile strength;

- Retained to temperatures in excess of 2000C;

- Resistance to creep;

- Relatively large fracture toughness;

- Low coefficient of thermal expansion; and high thermal

conductivity

Drawbacks:

- High-temperature oxidation

- Expensive

Manufacturing Techniques

- The hand layup technique

- The industrial manufacturing technique:

+ Compression molding, pultrusion, filament winding,

Resin transfer molding, etc.

+ Curing

+ Prepreg

Applications

• The US composite materials market forecast

The Aerospace Industry

• Automotive industry

- Glass fiber

• Sporting goods industry

• Marine Applications

• Consumer goods

- Short fiber composites

• Construction and civil structures

Quiz 1

1/ What is a composite material? Give 3 examples of

composite materials, show the matrix and reinforcing phase

in these examples.

2/ What are the functions of: Matrix, Fibers, Agents and

coatings in composites

3/ List 5 general characteristics of composite materials?

4/ What are 2 main and important differences between

polymer-matrix composites and metal-matrix composite.