Composites- Introduction to Matrices

Question 1

Functions of the matrix

Answer 1

Bind reinforcements together
Maintains shape
Transfers stress onto reinforcement
Protects reinforcement: chemical and moisture attack, mechanical abrasion.
Adds properties: toughness, shear (support against bending and torsional loading, compressive (support against buckling)

Question 2

What is the manufacturing of composites controlled by?

Answer 2

Processing of the matrix phase.
Viscosity, cure temperature, safety

Question 3

Typical order of considerations when choosing a matrix

Answer 3

1. Cost 2. Mechanical properties.
2. Service temperatures, compatibility with reinforcement, environmental resistance (chemical, moisture, UV), abrasion resistance, heat and electrical conductivity, appearance, processing

Question 4

What is the most common type of matrix and why?

Answer 4

Polymer matrices
Relatively easy fabrication
Low capital investment
Low tooling cost

Question 5

What are thermosets?

Answer 5

Thermosetting polymers. Ones that can’t be melted

Question 6

How to process thermosets how how to make thermosetting polymer composite parts

Answer 6

Polymerise them in-situ. Start with the monomers, combine them, combine with reinforcements, shape and cure (react monomers together) to solidify. Forms an amorphous, crisslinked or highly crosslinked polymeric structure.

Question 7

What is the resin?

Answer 7

Generally is the mixture of monomers before curing which becomes a polymer after the resin is cured although the terms are often used interchangeably

Question 8

What are the chemicals used to cure a resin called?

Answer 8

Curing agents or hardeners

Question 9

Why are thermosets the most common polymer type used in composites?

Answer 9

Primarily due to their low viscosity (before curing) which allows for excellent fibre impregnation and setting and high processing speeds

Question 10

Types of thermosets used as matrices

Answer 10

Unsaturated polyesters
Vinyl esters
Epoxies
Polyamides
Bismaleimides
Cyanate esters
Phenolics

Question 11

What is a thermoplastic polymer?

Answer 11

One that can be melted

Question 12

How to make thermoplastic polymer composite parts

Answer 12

Melt the polymer, combine it with the reinforcements, shape and solidify

Question 13

Why are only higher value thermoplastic materials typically used for composites?

Answer 13

Due to the cost of the reinforcements

Question 14

Types of thermoplastics used in composites

Answer 14

Polypropylene and polyamides (commodity thermoplastics)
Polysulfones
Polyimides
Polyketones
In order of lowest to highest tensile modulus and Tg (and generally cost)

Question 15

Advantages of thermosets over thermoplastics

Answer 15

Low viscosity reactants
Good adhesion with reinforcements
Thermal stability
Chemical resistance
Low creep

Question 16

Disadvantages of thermosets over thermoplastics

Answer 16

Limited shelf life
Long cure time
Low strain to failure

Question 17

Advantages of thermoplastics over thermosets

Answer 17

High impact strength
High fracture toughness
High strain to failure
Good shelf life
Short cure time

Question 18

Disadvantages of thermoplastics over thermosets

Answer 18

High melt viscosity
Low creep resistance
Low thermal stability

Question 19

What aspects of thermoplastics’ chemical and physical structure influences their performance?

Answer 19

Structure of the repeating unit (steric and electronic influences).
Higher molecular weight gives improved properties.
Entangled chains in amorphous thermoplastics give improved properties.
Aligned chains in semi-crystalline thermoplastics give improved properties

Question 20

Price to pay for improving properties of thermoplastic matrices

Answer 20

Processing is more difficult for ones with better properties