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40 Cards in this Set
- Front
- Back
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What is stress?
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Applied force / area
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What is strength?
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The max stress before fracture, opposite to strong is weak
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What is strain?
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Change in dimension due to stress
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On stress strain graph, what bit is toughness?
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Area under whole curve
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On stress strain graph, what bit is resilience?
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Area under curve before yield stress, the area absorbed by a material undergoing plastic deformation up to the elastic limit
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On stress strain graph, what bit is Young's Modulus?
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Gradient of bit before yield stress
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What is yield stress?
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Value after which permanent deformation occurs
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Difference between proof stress and proportional limit, what are they values of?
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Proof stress is an actual measured value of yield stress to cause x% of permanent deformation, for example 0.1% proof stress.
Proportional limit is an approximation worked out from graphs |
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What is Young's modulus?
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Also known as the modulus of elasticity, the gradient of the graph before yield stress is reached.
High = Rigid Shallow = flexible |
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On stress strain graph, what bit shows malleability/ductility?
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The value of strain between permanent deformation beginning and the fracture stress
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What is toughness?
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The total amount of energy a material can absorb up to the point of fracture
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What is the opposite to brittle?
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Tough
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What is fatigue limit
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Stress value below which a material survives cycles of stress indefinitely
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What is fatigue life
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Number of cycles survived by a material at a given value of stress
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What is hardness and how is it tested?
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Resistance to indentation under load. Diamond into a material at known force and measure the void left behind
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How do you calculate viscosity?
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Shear stress (pressure required to depress syringe barrel) / shear rate (flow rate out of syringe)
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What is a dilatant material?
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A material which as shear stress increases, viscosity also increases. Cornflour and water. Goes up on the graph.
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What is a newtonian material?
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A material which shear stress has no affect on viscosity
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What is a pseudoplastic material?
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As shear rate increases, viscosity decreases. Tomato ketchup
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What is thermal conductivity?
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Rate of heat flow per unit temperature gradient
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What is thermal diffusivity?
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How long it takes material to change to temp around it
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What is coefficient of thermal expansion?
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The fractional change in length per unit change in temp
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What stage of polymerisation does this describe:
'Decomposition of the initiation by thermal/chemical or radioactive means' |
Activation
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What stage of polymerisation does this describe:
'Radical formed on activation reacts with monomer' |
Initiation
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What stage of polymerisation does this describe: 'Reaction with further monomers'
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Propagation
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What stage of polymerisation does this describe: '2 active monomers come together, killing them'
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Termination
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3 ways which you can get x linking
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Chain transfer
Use cross linking agents Use a di or tri functional monomer |
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What is chain transfer
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the activity of a growing polymer chain is transferred to another molecule, if this other molecule is a polymer then this new chain might start halfway along the chain, making it branched
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How many functional groups are required to make a branched condensation polymer
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>2
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How can you reduce shrinkage in polymerisation
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Use fillers
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What sort of temperature change accompanies polymerisation reactions?
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Exothermic
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What is the glass transition temperature?
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Temperature at which the material goes from a hard and brittle state into a rubber like state
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What affect does adding phenol groups have on glass transition temp?
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Increases it
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What affect does adding si and o groups have on glass transition temp?
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Reduces it
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What is the relationship between molecular weight and Tg?
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Increased molecular weight = increased Tg
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What is the relationship between molecular weight and modulus of elasticity?
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Increased molecular weight = increased modulus of elasticity
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What is the relationship between branching and Tg?
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As branching increases, Tg decreases as the polymer chains can't get close together
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What has the higher Tg, polymethymethacrylate or polybutylmethacrylate?
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Polymethylmethacrylate
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What is the relationship between plasticisers and Tg?
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Lubricate movement of polymer chains and decrease Tg
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What is the relationship between plasticisers and youngs modulus?
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Reduce youngs modulus
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