What is rubber boi
- Natural rubber is an agricultural crop
- Synthetic rubber is based on petroleum
Why is rubber
a composite? idk
but there's a rubber matrix and then fibres
so polymer bitch!!! wait
isn't it all rubber. idk
what is vulcanization. why is it important.
the treatment that accomplishes cross linking of elastomer molecules
this process makes the rubber stiffer and stronger but retain extensibility - CROSS LINKING BOI!!!!! because when it's cross linked it reduced its ability to flow
- compounding - adding additives such as sulfur and fillers
- vulcanizing - treatment
whats a building drum (rubber)
prior to molding and curing, carcass is assembled on a building drum that rotates
how do you mold and cure tire
tire is placed over expandable
diaphragm, then split
mold is closed and the diaphragm inside expands to go against the mold. then the mold and diaphragm are heated to cure rubber
properties of composites
- - strong and stiff but light in weight
- - fatigue properties are generally better than for common engineering metals
- - toughness is greater
- - but expensive :(
- - manufacturing methods for shaping composite materials are slow and costly
how to make composite materials? general (primary phase and secondary phase)
- 1. Primary phase forms the MATRIX where the secondary phase is embedded
- 2. Secondary phase adds the REINFORCING AGENT because it strengthens the composite material
what types of composite materials are there
- 1. Metal Matrix Composites (MMCs) - mixtures of
- ceramics and metals, such as cemented carbides
- and other cermets
- reinforced by - particles of ceramic or fibres of other metals, ceramics
- 2. Ceramic Matrix Composites (CMCs) - Al2O3 and SiC
- imbedded with fibers to improve properties
- they high stiff, hard, and good compressive strength
- weaknesses: low toughness and bulk tensile strength, susceptible to thermal crackig
- 3. Polymer Matrix Composites (PMCs) - polymer resins
- imbedded with filler or reinforcing agent
- embedded as fibres, particles or flakes
- most important
- most common example is fibre reinforced polymers
what does the matrix material do
matrix shares load with the secondary phase and hides da fiber bois
in what forms does the reinforcing phase take on?
fibres, particles, flakes
what are fibres for reinforcing materials?
- - typically circular in cross section
- - greatest opportunity for strength
- - diameter ~0.0025 mm to 0.13 mm
fiberes - as diameter of fibre reduces...?
as diameter is reduced, the material becomes oriented in fibre axis direction; probability of defects in structure decreases significantly
difference between continuous fibres and whisker
continuous fibres are very long and can carry the load
discontinuous fibres (L/D = roughly 100)
whiskers - discontinuous of single crystals - 0.001 mm. v strong >:)
materials for fibres! x3
- glass - most widely used
- carbon - high elastic modulus
- boron - VERY high elastic modulus
- kevlar (a polymer babe)
what are particles and flakes /:
- particles are 3d smol boys
- flakes are 2d particles /: 2 faced
distribution is RANDON XD
what are CERMETS!
- MMC (not MCM)
- metal matrix composites with ceramic in a metallic matrix
ceramic is 96% in volume
can be divided in:
cemented carbides or oxide based cermets
what are CEMENTED CARBIDES
a type of cermets! most common one.
there are more than one carbide compounds bonded in a metallic matrix
- commonly based in
- - tungsten (W)
- - titanium (Ti)
- - chromium (Cr)
what are fibre reinforced polymers?
PMC consisting of polymer matrix embedded with high strength fibres.
Matrix: thermosetting plastic such as unsaturated polyester or epoxy, or thermoplastic such as nylons, polycarbonate
the fibres are discontinuous or continues and are often stacked in a laminar structure (stacking and bonding thin layers of fibre and polymer until desired thickness is obtained)
what are shaping processes of FRP?
reinforced polymers are shaped by...
- - open mold processes - similar to layup methods
- - closed mold processes - similar to plastic molding
- - filament winding - filaments dipped in liquid resin and wrapped around a rotating mandrel to produce a rigid, hollow cylindrical shape
- - pultrusion - similar to extrusion
how to make a PMC
matrix material made of thermosetting polymers or thermoplastic molding compounds.
all are reinforced with carbon black and mainly fibres
how can you combine matrix and reinforcement? (2 ways)
1. the starting materials arrive at fabrication separately; during shaping, they're combined
2. the two components are combined into some starting form can that then be used during shaping, such as molding compounds or prepregs
what are molding compounds
starts with matrix and reinforcement
resin matrix with random dispersed fibres which can then flow
like a bath of these bois
how to process molding compounds?
(hint: sheet molding compounds)
you make them into sheets using sheet molding compounds! the resin paste goes thru a series of rollers where choppers cut sum fibres in. this layuer is covered in another layer of resin.
all rolled up in a take up spool
what are prepregs
the second way to have matrix and reinforcement together!
these are fibers impregnated with partially cured TS resines to facilitate shape processing. refrigerated to inhibit curing
- prepregs are fabricated with continuous
- filaments rather than chopped random fibers, thus
- increasing strength and modulus
first shaping process: open mold processing
what are the three different lays to have open mold processes. what kind of composites are they used for
open lay up used a positive or negative mold surface. starting materials applied to mold in layers to desired thickness and then cured
- 1. hand lay up
- 2. spray up
- 3. automated tape-laying machines
used for fibre reinforced polymers, a type of polymer matrix composites!
what is the hand lay up method
- its a type of open mold shaping
- many layers manually applied to open mold
v labour intensive and finished mold must be trimmed w power saw
boat hulls and swimming pools are made of it
what is the spray up method
type of open mold shaping
liquid resin and chopped fibres are sprayed onto an mold mold to make layers. randomly oriented short fibres used
boat hulls, bathtubs
what is automated tape laying machines
machines that dispense prepreg tape on open mold following a programmed path
what are the three parameters for curing? what is curing?
curing cross links the polymer transforming it from liquid or highly plastic state in solid product
mostly done in room temperature in an autoclave
what are three classifications of closed mold processes?
- compression mold - mold sections brought together under pressure, forcing charge to take shape of cavity. mold halves heated to cure polymer
- transfer mold - charge of thermosetting resin w short fibres placed in pot or chamber which is then squeezed by ram action into mold cavities
- injection mold - thermoplastics, broken into two:
conventional injection molding: TP and TS, chopped fibres must be used
reinforced reaction injection molding: broken into: conventional reaction and reinforced reaction
conventional reaction - two reactive ingredients are mixed and injected into a mold cavity
reinforced reaction - same but has reinforcing fibres
what is filament winding
a type of shaping process
resin impregnated continuous fibers are wrapped around a rotating mandrel that has the internal shape of the desired product
resin cured and thn mandrel removed
- pulled from a resin bath
what are pultrusion processes? name two!
workpiece is PULLED through the die (rather than pushed - extrude)
- pultrusion - pull
- pulform - for curvy parts with varying cross sections
how does pultrusion work
continuous fibres dipped in resin bath & pulled thru shaping die
how does pulforming work?
pultrusion with an additional step to make curvy using a die shoe
what materials are used in pultrusion?
resins: epoxies, unsat. polyesters, silicones, all TS polymers