Uci Engr 54 Final Exam Gust Polymers And Composites

Front 1

What are crystalline polymers?

Back 1

These polymers are usually stronger and more resistant to dissolution and heat (compared to amorphous polymers,) have atomic arrangements more complex than in metals and ceramics because it involves molecules rather than atoms or ions.

Front 2

What is a character of simple and linear polymers?

Back 2

This characteristic is ease of crystallization?

Front 3

What are mechanical properties of polymers?

Back 3

These properties are in general (as compared to metals and ceramics) low tensile strenghth, low E, low hardness and high ductility (1000% elongation for some elastomers.)

Front 4

What is a polymer?

Back 4

This chemical is bonded by covalent interatomic bonds and van der Waals and/or hydrogen intermolecular bonds, and its class has a wide range of mechanical properties because there is a wide range of materials in this class.

Front 5

What are methods of increasing polymer strength?

Back 5

These methods are increasing crosslinking (crosslinks inhibit relative chain motion,) increasing cystallinity (more intermolecular secondary bonds are formed,) increasing molecular weight (longer chains have more strong chain bonds) and predeformation by drawing (permanent deformation in tension and analogous to strain hardening in metals.)

Front 6

What is a fiber reinforced composite?

Back 6

Its dispersed phase is in the form of a fiber. It is usually designed for specific strength or specific modulus (strength or modulus on weight basis.)

Front 7

It has a strengthening effect.

Back 7

What is an effect of increasing the fiber length?

Front 8

What is longitudinal loading?

Back 8

This process can have a maximum strengthening effect on composites.

Front 9

What is transverse loading?

Back 9

This isostress process

Front 10

What is a similarity between dispersion strengthening and precipitation hardening?

Back 10

These two processes both pin dislocations to make materials stronger.

Front 11

Precipitation hardening loses its effectiveness at high temperatures.

Back 11

What is a difference between dispersion strengthening and precipitation hardening?

Front 12

It fills in the smaller spaces.

Back 12

Why is sand used with gravel in concrete?

Front 13

What are strengthening methods in particle reinforced composites?

Back 13

Impeding dislocation motion (metal matrix composities) and stopping cracks are methods used methods used in composites.

Front 14

What are laminar composites?

Back 14

These materials contain series of sheets or panes, each with a preferred high strength direction. Its sheets are cemented together in such a way that the high strength direction varies from layer to layer. It is constructed in order to have a relatively high strength in virtually all direction within the laminate plane. Plywood is an example of this material.

Front 15

What are elastomers (rubbers?)

Back 15

These industrially important materials stretch under a low stress to at least twice their length and then quickly return to almost their original length upon removal of the stress.

Front 16

What is a plastic?

Back 16

This industrially important group of synthetic materials is processed my molding or forming into shape.

Front 17

What are thermoplastics?

Back 17

These materials require heat to make them formable, retain shape after cooling, can be reheated and reformed, have low density, are easy to process, have good resistance to corrosion and chemical attack and include nylons, polycarbonates, polyethylene, polypropylene, polystyrene and acrylic.

Front 18

What are thermosetting plastics (thermosets?)

Back 18

These materials require heat to be permanently 'set' palctic, can't be recycled (properties degrade when materials reheated,) have high elasticity and dimensional stability, are denser, more brittle, stronger and harder than thermoplastics and include phenolics and epoxy resins.

Front 19

What are branched polymers?

Back 19

These chemicals have side branch chains that are connected to main chains and have reduced chain packing efficiency (lower density.)

Front 20

What are crosslinked polymers?

Back 20

These chemicals have adjacent linear chains that are joined at various places by covalent bonds.

Front 21

What are network polymers?

Back 21

These chemicals are made of highly crosslinked, three dimensional networks.

Front 22

What are copolymers?

Back 22

These chemicals are made of two or more different repeating units.

Front 23

What is a random copolymer?

Back 23

This chemical is made different sets of repeating units randomly arranged within its chain.

Front 24

What is an alternating copolymer?

Back 24

This chemical is made of different sets of repeating units that alternate along its chain.

Front 25

What is a black copolymer?

Back 25

This chemical is made of different sets of repeating units in a chain that are made of relatively longs blocks of each type.

Front 26

What is a graft polymer?

Back 26

This chemical has appendages of one set of repeating units that a grafted to a long chain of another set of repeating units.

Front 27

What is the degree of polymerization?

Back 27

This variable is used to express the average chain size of polymer.

Front 28

What is crystallinity?

Back 28

This characteristic is influenced by chain configuration and molecular chemistry.

Front 29

What are polymers that are difficult to crystalize

Back 29

These polymers have complex mer structures and fall in the branched or crosslinked class or the alternating or block copolymer class.

Front 30

What are polymers that are USUALLY amorphous?

Back 30

These polymers fall in the network polymer class or the random or graft copolymer class.

Front 31

that of Hooke's law

Back 31

What behavior do the mechanical properties of polymers follow at low temperatures?

Front 32

viscous flow (liquid like)

Back 32

What behavior do the mechanical properties of polymers follow at high temperatures?

Front 33

viscoelastic

Back 33

What behavior do the mechanical properties of polymers follow at intermediate temperatures?

Front 34

What is visoelasticity?

Back 34

This variable has instantaneous elastic strain and viscous flow, is dependent on time and temperature and quantified using stress relaxation measurements.

Front 35

What is stress relaxation?

Back 35

This property occurs when a material held at a constant temperature is rapidly pulled to a certain strain level and the stress necessary to maintain that strain and the material's energy state decrease with time. It is a result of polymer chains sliding by each other by breaking and reforming secondary bonds between chains and by mechanical untangling and recoiling of chains.

Front 36

changes in chemistry and processing techniques

Back 36

How can methods of increasing polymer strength be achieved?

Front 37

What is kevlar?

Back 37

This material made of synthetic aramid fibers is part of the nylon family and was discovered by Stephanie Kwolek and Herbert Blades at Dupont in 1965. Its fibers consist of long molecular chains produced from poly-paraphenylene terephthalamide (highly oriented.) In its manufacturing its polymer is dissolved in solution and spun into fiber using a spineret.

Front 38

What are prop

Back 38

These properties are high tensile strength relative to its weight, a stiffness (high elastic modulus,) high chemical resistance, low thermal shrinkage, high toughness, excellent dimensional stability, high cut resistance and flame resistance (self-exstinguishing.)

Front 39

What are applications of Kevlar?

Back 39

These applications are bullet proof vests, cut resistant gloves, anti-mine boots, helmets, motorcycle apparel, kayaks (better impact resistance with no extra weight,) automotive hose, airplane cabin panels, run-flat tires, fishing lines and brake pads