ENGI1002 - Topic 6

What is a composite?

A composite is a multiphase material with significant presence of each phase.

What is the matrix?

Matrix is the continuous phase. It transfers stress to the dispersed matrix and protects it.

What does the dispersed phase do?

Dispersed phase raises E, yield, tensile strength, creep resistance.

What are the composite classifications?

• MMC - metal

• CMC - ceramic

• PMC - polymer

What are the types of composites?

• Particle reinforced composites

• Fibre reinforced composites

• Structured composites

What are the two types of particle reinforced composites?

• Large-particle

• Dispersion strengthened

What are the two types of fibre reinforced composites?

• Continuous (long) fibres

• Discontinuous (short/random) fibres

Continuous fibres advantage?

Continuous fibres give maximum strength in one specific direction.

Discontinuous fibres advantage?

Discontinuous fibres give weaker but even strength all the way around.

What is isostrain?

Isostrain is load transferred from matrix to fibre.

What is isostress?

Isostress is same stress to composite and both phases.

Property of aligned fibre composites?

Aligned fibre composites are anisotropic.

What are the loading conditions in fibre composites?

• Longitudinal loading: Isostrain

• Transverse loading: Isostress

Why is composite failure not catastrophic?

Composite failure is not catastrophic because fibres do not break all at once.

What are laminar composites?

Laminar composites are stacked and bonded fibre-reinforced sheets.

Benefits of laminar composites?

• Balanced

• In-plane stiffness

Sandwich panels advantages?

Sandwich panels give low weight and large bending stiffness.

What is the most common composite?

Particle reinforced composites are the most common form of metal matrix composites.

Carbon fibre composite properties?

• Highest specific modulus and specific strength of all reinforcing fibre materials.

• Half the density of aluminium.

What is a carbon fibre matrix?

A carbon fibre matrix is an amorphous thermoset polymer.

How to minimise anisotropy in carbon fibre composites?

To minimise anisotropy, CFC are woven into fabrics with the right alignment.

What is timber?

Timber is composed of cellulose tracheids in an amorphous lignin matrix.

Timber properties?

• 50x stiffer along the grain than across it.

• Strength depends on moisture content.

• Timber stores carbon.