Definitions Flashcards
(29 cards)
Define gelation:
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.
Define vitrification:
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.
Define glass transition temperature:
Temperature over which a polymer switches from a glassy to a rubbery state.
Define contiguity factor:
Value that relates the arrangement and aspect ratio of inclusions to the overall material response.
Define thermoset:
A polymer made up from cross-linked long chains to form a 3D network of permanent bonds, that is obtained by irreversible hardening.
Define thermoplastic:
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.
Compare thermosets and thermoplastics chemical makeup:
Thermosets - strong crosslinks between chains
Thermoplastics - weak intermolecular forces between chains
Define toughness:
Ability of a material to absorb energy and plastically deform without fracturing.
A measure of resistance to crack formation and growth.
Define tow:
An untwisted bundle of continuous fibres.
Define woven fabric:
Woven fibres in different directions that cross over and under each other, like fabric, with hundreds of variations.
Define non-crimp fabric (NCF):
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.
Define pre-preg:
A partially cured thermoset matrix, stored at low temperature for subsequent use (to slow down curing process).
Define a representative volume element (RVE):
The smallest possible portion that contains all constituents of a material.
Define the Voigt-Reuss-Hill average:
A simplistic approach to estimating the effective moduli by taking the average of the Voigt and Reuss bounds.
Define Voigt bound:
A theoretical upper- bound of properties for axial loading.
RoM.
Define Reuss bound:
A theoretical lower- bound of properties for transverse loading.
IRoM.
Define Hashin-Shtrikman bounds:
Tighter limits of the elastic moduli and tensors of composites.
What does the Composite Cylinder Assemblage Model (CCA) consist of?
An infinite number of concentric cylinders of different diameters, packed together to fill the volume of composite material.
Define critical length:
Fibre length such that pull-out and fracture failure occur simultaneously.
What is the purpose of the Eshelby Equivalent Inclusion:
Can calculate either the strain or stress concentration tensors for more complex composite models between the Voigt (upper) and Reuss (lower) bounds.
What does the Mori-Tanaka model predict?
Behaviour of non-dilute (highly filled) composites.
What does Self Consistent model predict?
Behaviour when volume fraction is extremely high.
Define self-healing composites:
Automatically healing response following damage, inspired by biological systems.
Define capsule-based self-healing:
Microcapsules of resin and hardener are embedded in a composite.
Once a crack propagates through the capsules, they flow out, mix and harden.
