T5 Flashcards
What is a ceramic?
A class of material which have low toughness, high hardness, resistance to corrosion/high temps, and are thermal/electrical insulators.
Why is it important to grind cement into a thin powder?
It increases SA. The hydration reactions between water/cement happen at surface of cement particles so it allows more bonding to occur.
What is glass crystallisation?
Where glass transforms into a crystalline solid, usually by heat treatment. This improves the strength of the glass and causes a lower coefficient of thermal expansion.
Why are borosilicate glasses and fused silica resistant to thermal shock?
They have relatively low coefficients of thermal expansion so upon heating or cooling, the difference in expansion or contraction is low.
What’s the difference in strengthening mechanism between large particle and dispersion strengthened larger particle reinforced composites?
Large particle: the particle matrix interactions aren’t treated on a molecular level. Matrix transfers load to particle which is stiffer
Dispersion strengthening: interactions on molecular level. Strengthened by preventing dislocation movements
Why below a certain length of fibre in a polymer reinforced composite are the improvements in strength reduced?
Force transmittance from the matrix to the fibre is too low due to end effects.
How are precipitation hardening and dispersion strengthening similar?
They both hinder dislocation motion
How are precipitation hardening and dispersion strengthening different?
The strengthening effect isn’t maintained at high temps for precipitation.
The strength is developed by a heat treatment for precipitation hardening
3 functions of a matrix phase for a polymer matrix fibre reinforced composite
1) bind fibres together so applied stress is evenly distributed among fibres
2) protect the surface from being damaged
3) to separate the fibres and inhibit crack propagation
What are the desired characteristics of the matrix and fibre phase of a polymer matrix fibre reinforced composite?
Matrix phase must be ductile and soft
Fibre phase must be stiff and strong
Why must there be a strong bond between fibre and matrix at their interface?
To maximise stress transmittance between matrix and fibre phases
To minimise fibre pull-out and the chance of failure
Why are fibre glass reinforced composites used extensively?
Glass fibres are cheap to produce
Composites can have high specific strengths
They are chemically inert
What are the limitations of fibre glass reinforced composites?
Care taken to handle fibres as they may get surface damage
They lack in stiffness compared to other fibrous composites
Limited by high temps
Three kinds of composites
Particle reinforced
Fibre reinforced
Structural
Types of particle reinforced composites
Large particle
Dispersion strengthened
