MECH 3503 - Composites

• 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

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 
• mixing
• shaping
• vulcanizing - treatment

prior to molding and curing, carcass is assembled on a building drum that rotates

uncured 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

• - 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

• 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

• 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

matrix shares load with the secondary phase and hides da fiber bois

fibres, particles, flakes

• - typically circular in cross section
• - greatest opportunity for strength
• - diameter ~0.0025 mm to 0.13 mm

as diameter is reduced, the material becomes oriented in fibre axis direction; probability of defects in structure decreases significantly

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 >:)

• glass - most widely used
• carbon - high elastic modulus
• boron - VERY high elastic modulus
• kevlar (a polymer babe)

• particles are 3d smol boys
• flakes are 2d particles /: 2 faced

distribution is RANDON XD

• 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

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)

Wcriti

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)

fibre 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

matrix material made of thermosetting polymers or thermoplastic molding compounds.

all are reinforced with carbon black and mainly fibres

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

starts with matrix and reinforcement 

resin matrix with random dispersed fibres which can then flow 

like a bath of these bois

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

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

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!

• 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

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

machines that dispense prepreg tape on open mold following a programmed path

curing cross links the polymer transforming it from liquid or highly plastic state in solid product 

mostly done in room temperature in an autoclave 

• time 
• temprature
• pressure

• 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

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 
• 

workpiece is PULLED through the die (rather than pushed - extrude)

• pultrusion - pull
• pulform - for curvy parts with varying cross sections

continuous fibres dipped in resin bath & pulled thru shaping die 

pultrusion with an additional step to make curvy using a die shoe

resins: epoxies, unsat. polyesters, silicones, all TS polymers 

reinforcing: e-glass