Midterm Flashcards
(22 cards)
3 types of epoxy curing agents
- Amines (90% of hardners)
- Anhydrite-slow cure, good electrical and heat properties
- Lewis Acid
Amine hardeners (2 types and functions)
- Aliphatic- room temp cure
- Aromatic- High performance hardner, thermal cure, slightly better mechanical properties
Calculating epoxy stoichiometry with amine curing agents
First figure out epoxide equivalent weight (EEW also called WPE):
EEW= molecular weight of epoxy / # of epoxide groups
Next find the amines hydrogen equivalent weight (HEW):
HEW=molecular weight of amine / # of amino hydrogens (an amino hydrogen is a hydrogen attatched to a nitrogen)
Then calculate stoichiometry:
Parts per hundred of amine (PHR)= (HEW / EEW) *100
(the result is how many parts amine hardner per hundre parts of epoxy)
Vitrification
Vitrification is when curing slows/stops because of impeded molecular mobility, which prohibits the hardner from reacting with the resin.
- Achieved Tg is going to be the max Tg of the resin or dependant on what temp the resin is cured at, whichever is less.
- This is why most high performance epoxies have an elevated temperature cure.
High performance epoxies (Types and characteristic)
- TGDDM and DGEBA
- high crosslink desnity= high Tg and thermal properties
- more epoxide rings= more bonding sites= higher crosslink density
Rubber Toughening- process and type of rubber used
- Adding rubber particles to resin
- rubber particles increase size of crack tip, reducing crack propegation
- carboxy terminated butadine nitrile rubber (CBTN) is the most common type of rubber hardner for epoxies, its soluable in the resin
Vinylester structure and uses
- starts as epoxy, epoxide groups are reacted away allowing for crosslinking with catalyst.
- slightly better mech/thermal props than polyetser
- good chemical resistance
Cyanate esters- properties/uses
- simlar mechanical properties to epoxy
- much better than epoxies in hot/wet conditions
Polyimids- uses/properties
- Very high service temps
- bismaleimides-addition reaction= no condesnate= no voids
Phenolics- uses/properties
- flame retardant
- condensation reaction- lots of h20 created
Aramid Properties
- Impact resistance
- very high specific strength (500 ksi @ 1.44 g/cm3)
- absorbs lots of water from the enviroment
- poor compressive strength- fibrillar failure
- hard to cut
carbon fiber properties
- High specific stiffness (1.8g/cm3)
- classifications of carbon fibers (tensile strength)
- standard modulus= 30-35 msi
- intermediat modulus= 40-45 msi
- high modulus= 50-70 msi
- ultra high modulus= 70+ msi
- higher modulus fibers have more ideal circular carbon structure
Boron properties
- 58 msi @ 2.57 g/cm3
- very high compressive strength = 1000ksi (2x tensiles)
- will splinter and impale you
6 things you want to happen in an autoclave
- consolidation
- void removal
- removal of volatiles (H20, solvents and gasses)
- cure the resin
- fiber wetout
- removal of excess resin
3 autoclave variables
- pressure- autoclave and vacuum pressure
- temperature- ramp rates, soak temp, headspace and part temp
- Time- soak and pressure time
3 most common autoclave gasses
- Nitrogen- most commmon, not flamable, will suffocate you becuase its not air
- Air- free but supports combustion- max temp= 250F
- C02- uncommon, safer than nitrogen because body can sense it
3 common types of process controllers
- proportional controller
- derivative control
- integral control
PID controller
proportional, integral, derivative controller
- uses a combination of each control method, will cometimes overshoot temp slightly then bring it down
Resin cure cycle
- start as viscous liquid
- as resin is heated viscosity decreases
- as time progresses temp increases and viscosity goes down but molecular weight increases
- resin viscosity can is thermally dominated at begining of cycle then cure dominated later
the 4 tropics
- isotropic- props the same in all directions
- anisotropic- props not the same in all directions
- quasiisotrpic- props the same in all directions in the x-y plane
- orthotropic- one set of mutually perpendicular planes of symmetry
3 types of coupling and how to avoid them
- Tensile-shear
- tensile load results in a shear deformation
- a shear load results in a tensile deformation
- avoid by balancing laminate
- tensile bending
- a tensile load results in a bending deformation
- a bending load results in a tensile deformation
- to avoid use symmetric laminates
- bending - twisting
- a bending load results in a twisting deformation
- a twisting load results in a bending deformation
- to avoid- for every ply in the positive direct there must be an equivalent negative ply equidistand from the midplane
edge effects
- difereing poisons ratio’s between layers can cause stresses and interlamniar shear, which is concentrated near holes or at the edge of the laminate. Edge effects can cause cracking or delamination.
