Composites Flashcards
what are the two types of composites?
particulate and fiber reinforced (FR)
what are the primary components of FRC?
matrix - bulk material surrounding the fibres
fibres - reinforcement for the matrix (tension)
interface - contact between matrix and fibres
additives - anything added in order to produce a desired effect
name three example of matrix materials
polymers
HCP
metals
ceramics
name 3 examples of fiber materials
glass
polyethylene
steel
carbon (graphite)
what are the characteristics of unidirectional fibre configurations?
Most common for structural
Highly unidirectional
Anisotropic!!
Like wood
Fibres run in one direction
what are the characteristics of two-directional fibre configurations?
more isotropic
discontinuity is weaker in longitude but stronger everywhere else. lose strength in one direction but grain strength in other.
what is the purpose of a matrix?
maintains shape
helps in compression
conduct or resist electricity
tensile stress transfer
protect reinforcement from environment
what is the purpose of the fibers?
provide strength
increase stiffness
improve energy absorption
damage/ crack takes away the energy from the body
explain how kevlar works
by energy absorption
bulletproof vests slow down the bullet until it stops moving
damage is not reparable (gotta throw it out after one use)
also how helmets work
what is the purpose of the interface?
stress transfer between matrix and fibre
interphase is when interfacial contact region is a distinctly separate phase
what are the purposes of additives?
ffpls
fire retardant (inhibit toxic burning)
filler (improve mechanical properties and reduce cost)
plasticizer (lower glass transition temp)
lubricant (improve mixing and lower friction)
stabilizer (improve resistance to heat, UV, and oxidation)
what are the three important characteristics for high performance fiber?
small diameter (diameter ↓ tensile strength ↑)
high aspect ratio (surface area to volume changes with aspect ratio PLATELET AND FIBRE)
high flexibility (high E and small diameter)
why is it useful to fibre reinforce polymers?3
- reduce creep
- thermosets: give warning before failure rather than failing brittley
- carry loads that thermosets can’t
when cracking begins, material becomes porous and can’t transmit fluids withot leaking
what is the advantage of FRPs in terms of tailoring properties?
Properties tend to be anisotropic
You can tailor which direction is strongest and tailor how you attach it to the structure to benefit from the strength
Only needs to be strong in directions you need it to be strong
what are some advantages of FRPs? 6
high specific strength
high specific stiffness
low density (good for dead load)
made into complex shapes
insulate (except for carbon fibre)
not reactive (prosthetics)
