Examen Final

Question 1

Thermoset polymers result from a “phase transformation” reaction which generates only a low degree of spatial crosslinking.

Answer 1

FALSE

Question 2

Undercooling is defined as the difference of Treal minus Tequilbrium

Answer 2

FALSE

Question 3

Bainite is a coarser microstructure than pearlite, and thus harder and tougher.

Answer 3

FALSE

Question 4

Malleable cast iron is the result of heat-treating a white cast iron which typically has a carbon equivalent of 3 to 3.4%

Answer 4

TRUE

Question 5

The Avrami equation (K-J-M-A) is a mathematical model of the effect of time on a phase transformation process at a given temperature.

Answer 5

TRUE

Question 6

When adding lateral groups to a polymer, as the case of PVC instead simple polyethylene, the transition temperature increases and as well as its ability to crystallize.

Answer 6

TRUE

Question 7

The Weibull distribution is a statistical function that is used, amongst many other applications, to predict the hardness of ceramic of Volumen V0 whose material has a characteristic stress S0 and a sensitivity exponent m.

Answer 7

FALSE

Question 8

For recrystallization to occur on annealing of a metallic alloy, a minimum amount of temperature is required, otherwise grain growth will set in.

Answer 8

FALSE

Question 9

In XYZZ designation of steels (AISI-SAE) X is the type of the steel, Y the modification and ZZ the carbon content in hundredths of a per-cent

Answer 9

TRUE

Question 10

In a two-phase material consisting of a matrix and secondary particles that exist in thermodynamic equilibrium the larger particles tend to integrate smaller once (large particles
“eat” little once). Why is this tendency?

Answer 10

R=Because the surface energy increases with D 2 and internal energy decreases with D 3

Question 11

The dihedral angle between two phases is what controls the rate of transformation of
the new phase.

Answer 11

FALSE

Question 12

The speed at which the martensitic transformation occurs is controlled by diffusion in the solid alloy.

Answer 12

FALSE

Question 13

Sinterization is a solid state process which densifies a particulate material. The processis self-diffusion driven, diffusion which arises because of a:

Answer 13

R= surface energy reduction.

Question 14

Atactic polymers tend to be less crystalline than the isotactic or syndotactic once.

Answer 14

TRUE

Question 15

Titanium has a higher specific stiffness than steels.

Answer 15

FALSE

Question 16

Copper alloys can be strengthened by deformation, solid solution, grain size reduction,
and / or precipitation of secondary phase particles.

Answer 16

TRUE

Question 17

Homogenization is a product of the redistribution of solute in the solid material as it is
cooled during certain periods of time.

Answer 17

FALSE

Question 18

The PVC and polystyrene are more resistant than polyethylene because links within their chains are stronger.

Answer 18

FALSE

Question 19

The dihedral angle formed between two adjacent phases is a function of their melting
temperatures.

Answer 19

FALSE

Question 20

A simple, binary, eutectic phase diagram presents only one solid phase.

Answer 20

FALSE

Question 21

Get high hardness and

toughness simultaneously in martensite.

Answer 21

TEMPERING

Question 22

Reach maximum hardness in steels.

Answer 22

QUENCHING

Question 23

Soften metals which produce precipitates on slow cooling.

Answer 23

HOMOGENIZIRING

Question 24

Relieve residual stresses.

Answer 24

PRONCESS ANNEALING

Question 25

Hardening solid solutions by precipitation.

Answer 25

AGEING

Question 26

Improve machinability of steels with medium and high carbon.

Answer 26

SPHEROIDIZING.

Question 27

Recrystallize cold worked | microstructures.

Answer 27

ANNEALING

Question 28

Refine grain size.

Answer 28

NORMALIZING

Question 29

Maximize strength and | toughness in medium carbon steels.

Answer 29

AUSTEMPERING

Question 30

Harden only the surface of a low carbon steel.

Answer 30

CARBURIZING AND QUENCHING

Question 31

Keeping in mind the state of strain and stress, and the cost of the component; what kind of composite material would you use to manufacture a control surface (aileron) for airplanes?

Answer 31

Long unidirectional fiber laminates stacked in different orientations.

Question 32

the firewall of a motorcar | (wall separating the enginecompartment from thepassengers compartment)?

Answer 32

Short random | orientation fiber.

Question 33

a horizontal panel for a home cabinet or wardrobe close

Answer 33

Honeycomb sandwich.

Question 34

0a storage tank for high | pressure air?

Answer 34

Long wound fiber | filament winding

Question 35

A simply supported beam | under flexion?

Answer 35

Long unidirectional fiber.

Question 36

the engine hood of a tractor trailer?

Answer 36

Short random orientation fiber.

Question 37

the washing sink in a hairdressers shop?

Answer 37

Short random orientation fiber.

Question 38

the lid of a domestic water | tank?

Answer 38

Short random orientation fiber.

Question 39

``` front fender (panel that extend from the front bumper to the car's doors) a compact car? ```

Answer 39

Short random orientation fiber.

Question 40

a suspension arm for an | off-road vehicle?

Answer 40

Long unidirectional fiber.

Question 41

The elastomers typically acquire mechanical properties by crosslinking through sulfur atoms.

Answer 41

TRUE

Question 42

The more severe the quench media, the larger the critical diameter of a given steel.

Answer 42

TRUE

Question 43

The critical diameter of a steel is the one that produces 50% ferrite at the center of a properly quenched cylindrical rod.

Answer 43

FALSE

Question 44

The Arrhenius equation relates the fraction transformed with time and temperature at which this transformation occurs.

Answer 44

TRUE

Question 45

The density of Ti-based superalloys is greter than that of low alloy steels.

Answer 45

FALSE

Question 46

``` The amount of- and rate of nucleation of a new phase within an existing phase is function of the undercooling present. ```

Answer 46

TRUE

Question 47

During solidification, the position of the liquidus line will be depressed with increasing undercooling, and this is because the diffusion in the liquid is slower that in the solid.

Answer 47

FALSE

Question 48

Crystallization of plastic is easier if the degree of polymerization is high

Answer 48

TRUE

Question 49

A copolymer is an alloy of two or more types of polymers.

Answer 49

FALSE

Question 50

Ceramic glasses can suffer dynamic as well as static fatigue.

Answer 50

TRUE

Question 51

Crystallization of plastic is easier if the degree of polymerization is high.

Answer 51

TRUE

Question 52

Thermodynamics tells us what phases are to be formed and kinetics provides information on the morphology of the new phases.

Answer 52

FALSE

Question 53

Obtuse precipitates are better reinforcers than acute ones.

Answer 53

TRUE

Question 54

Thermal shock resistance is measured as the maximum temperature a material can resist without cracking.

Answer 54

FALSE

Question 55

Hardenability of steels can be measured with a Vickers quench test.

Answer 55

FALSE

Question 56

Solid solution strengthening is because the deformations of the lattice introduced by the foreign atom reduce the mobility of vacancies.

Answer 56

FALSE

Question 57

In low alloy steels, the modulus of elasticity is a function of carbon content.

Answer 57

FALSE

Question 58

The eutectoid pearlite structure is formed faster than the eutectic ledeburite structures.

Answer 58

FALSE

Question 59

For an alloy to be adequately strengthened by precipitation of a secondary phase, it must have an appreciable maximum solubility of the solute at high temperature and much lower maximum solubility at room temperature.

Answer 59

TRUE

Question 60

The phase rule of Gibbs states: C=F + P + 2

Answer 60

FALSE F=C-P+2

Question 61

How much eutectic is present in a A-30% B alloy which solidified in equilibrium and is held at 180⁰C?

Answer 61

R = 1/4 ó 25%

Question 62

The thermoset polymers exhibit a steeper softening behavior than thermoplastic polymers.

Answer 62

FALSE

Question 63

The apparent porosity of ceramic material is usually smaller than the true porosity.

Answer 63

TRUE

Question 64

Copolymers are "alloys" of momomers which generally have better mechanical properties than their individual components.

Answer 64

TRUE

Question 65

Nickel base super-alloys have a similar specific strength than low alloy steels.

Answer 65

TRUE

Question 66

The toughness of polymers is the same as that of metals.

Answer 66

FALSE

Question 67

Martensite of steels is a metastable solid solution with a body-centered cubic structure.

Answer 67

FALSE

Question 68

A phase is material which has a specific structure and atomic arrangement, is homogeneous in composition and properties, and exhibits a defined interfaces with other phases.

Answer 68

TRUE

Question 69

The M s and M f temperatures of carbon steels depend on the C content, and tend to increase with increasing C content.

Answer 69

FALSE

Question 70

The peritectic reaction involves a liquid that becomes a new liquid plus a new solid.

Answer 70

TRUE

Question 71

Ceramic materials have difficulty to deform elastically because their Burgers Vector is usually large.

Answer 71

FALSE

Question 72

Of the 4 Hume-Rothery rules for infinite solubility the most important factor is the valence rule.

Answer 72

FALSE

Question 73

The electrical conductivity of polymers is similar to that of metals.

Answer 73

FALSE

Question 74

1. Ceramic powder mining or synthesis 2. Grinding to a specific granulometry 3. Mixing with plasticizer and additives 4. Forming of the product 5. Binder removal 6. Densification by sintering 7. Post-processing

Answer 74

ORDEN 1 A 7