Definitions

Question 1

Define gelation:

Answer 1

The point that polymer chains start to crosslink and form a 3D network.
Resin is in rubbery state and viscous flow is no longer possible.

Question 2

Define vitrification:

Answer 2

Glass formation due to Tg increasing from below to above Tcure as a result of reaction. Resin is in glassy state with high mechanical properties.

Question 3

Define glass transition temperature:

Answer 3

Temperature over which a polymer switches from a glassy to a rubbery state.

Question 4

Define contiguity factor:

Answer 4

Value that relates the arrangement and aspect ratio of inclusions to the overall material response.

Question 5

Define thermoset:

Answer 5

A polymer made up from cross-linked long chains to form a 3D network of permanent bonds, that is obtained by irreversible hardening.

Question 6

Define thermoplastic:

Answer 6

A polymer made by joining many monomers together to form long chains using a process called polymerisation, that can be softened and processed through heating.

Question 7

Compare thermosets and thermoplastics chemical makeup:

Answer 7

Thermosets - strong crosslinks between chains
Thermoplastics - weak intermolecular forces between chains

Question 8

Define toughness:

Answer 8

Ability of a material to absorb energy and plastically deform without fracturing.

A measure of resistance to crack formation and growth.

Question 9

Define tow:

Answer 9

An untwisted bundle of continuous fibres.

Question 10

Define woven fabric:

Answer 10

Woven fibres in different directions that cross over and under each other, like fabric, with hundreds of variations.

Question 11

Define non-crimp fabric (NCF):

Answer 11

In these fabrics each laminae are arranged with mats of straight fibres.
Alternate laminae in different directions are connected to each other via intermittent
stitching.

Question 12

Define pre-preg:

Answer 12

A partially cured thermoset matrix, stored at low temperature for subsequent use (to slow down curing process).

Question 13

Define a representative volume element (RVE):

Answer 13

The smallest possible portion that contains all constituents of a material.

Question 14

Define the Voigt-Reuss-Hill average:

Answer 14

A simplistic approach to estimating the effective moduli by taking the average of the Voigt and Reuss bounds.

Question 15

Define Voigt bound:

Answer 15

A theoretical upper- bound of properties for axial loading.

RoM.

Question 16

Define Reuss bound:

Answer 16

A theoretical lower- bound of properties for transverse loading.

IRoM.

Question 17

Define Hashin-Shtrikman bounds:

Answer 17

Tighter limits of the elastic moduli and tensors of composites.

Question 18

What does the Composite Cylinder Assemblage Model (CCA) consist of?

Answer 18

An infinite number of concentric cylinders of different diameters, packed together to fill the volume of composite material.

Question 19

Define critical length:

Answer 19

Fibre length such that pull-out and fracture failure occur simultaneously.

Question 20

What is the purpose of the Eshelby Equivalent Inclusion:

Answer 20

Can calculate either the strain or stress concentration tensors for more complex composite models between the Voigt (upper) and Reuss (lower) bounds.

Question 21

What does the Mori-Tanaka model predict?

Answer 21

Behaviour of non-dilute (highly filled) composites.

Question 22

What does Self Consistent model predict?

Answer 22

Behaviour when volume fraction is extremely high.

Question 23

Define self-healing composites:

Answer 23

Automatically healing response following damage, inspired by biological systems.

Question 24

Define capsule-based self-healing:

Answer 24

Microcapsules of resin and hardener are embedded in a composite.
Once a crack propagates through the capsules, they flow out, mix and harden.

Question 25

Define vascular-based self-healing:

Answer 25

A network of hollow fibre containing either resin or hardener intertwine through a composite, created using sacrificial scaffolds or via 3D printing.
Once a crack propagates the capsules are opened so the liquid resin and
hardener/catalyst flows out, mixes and hardens.

Question 26

Define intrinsically self-healing:

Answer 26

Thermoplastics with a low-melting point just above service temperature are added to a thermoset, and can flow to fill cracks when slightly heated.

Question 27

Define the percolation theory:

Answer 27

Explanation for the electrically conducting behaviour of composites consisting of conducting fillers and insulating matrices under the correct dispersion and volume fraction conditions.

Question 28

Define debulking:

Answer 28

Process to remove air and increase volume fraction after laying prepreg or fabric over a tool.

Question 29

Define an autoclave:

Answer 29

A pressure vessel used to pressurize and cure a composite part and increase it’s volume fraction.