Properties of Materials

An element has a density of 9.8Mg/m^3, an atomic radius of 0.143nm, and an atomic weight of 209g/mole. In its solid crystalline form, what is the packing factor for this element? Avogadros number is 6.022 x 10^23

0.35

The carbon content of pearlite is

0.76% wt. % Carbon

Which of the following steels has the highest austenization temperature

1020 (lowest carbon content)

The qe of a Jominy bar of which of the following steels should be the hardest?

1055 (highest carbon content)

At equilibrium, which of the following materials consists of a single solid phase?

1080 steel at 728 degrees celcius

Thin wires of the four carbon steels shown in #8 are austenitized and water quenched. Whihc steels would have the highest as quenched hardness?

1080 steel because it has the highest carbon content

The compound A2X3 contains 50 weight % of element A and 50 weight % element X. Element A has a mass of 25 g/mol. What is the atomic mass of element X?

16.7 g/mol

Find the ratio of weight to number average molecular weight of four polymer molecules with the following molecular weights: 1000, 1000, 1000, and 10000 g/mol

2.4

Element X crystallizes in an orthorhombic arrangement, which is a "box" with all internal angles equal to 90 degrees, but with the dimensions of the box being a not equal to b not equal to c (so not a cube). If element X weighs m grams per mole, its atomic radius is rx, and there are 2 atoms per unit cell, what is the theoretical density of X? Na is avogadro's number.

2m/(abcNa)

A 60Cu-40Ni plate is rolled at room temperature, from an original thickness of 20mm to a final thickness of 12 mm. The plate has undergone

40% cold work.

CuAl2 is an important compound in certain certain aluminum alloys. what is the weight % of Al in CuAl2? The atomic weight of Cu is 63.5 g/mol, and the atomic weight of Al is 27.0

46

A TDM metal with sigma yield = 1000MPa is stressed in tension to 400 Mpa. The corresponding strain is 0.008. What is the elastic modulus of this metal?

50 GPa

"There is no free lunch." When you make a metal much stronger, its ductility usually goes way down. Which of the following is an exception? In other words, for which of the following is the first material not much less ductile than the second?

60Cu-40Ni is stronger than 100 Cu

An unknown polymer in the form of a thin flat circular disk, is put through the "cooking" test from our polymers lab. At room temperature, the disk is relatively transparent. As the disk is heated, the sharp-eye (and sharp-tweezered) students observe the following behavior.

80 degrees C the disk changes shape, becoming somewhat football shaped and curving up off the heating plate. The glass transition temperature

According the Fe-Fe3C phase diagram which of the following temperatures is closest to but above the austenization temperature of 1050 steel?

800 degrees C

An element has an atomic radius r and atomic weight A. Na is avogadro's number. the ratio A/Na/(4/3)pir^3 represents

A number greater than the theoretical density of the element

Which of the following sets of properties are most closely related to the atomic bond strength of an element? (note: E=elastic modulus, alpha= coefficient of thermal expansion, Tm=melting temperature, sigma y=yield strength, and sigma u=ultimate strength)

E, alpha, and Tm

A tensile test is performed on a TDM dogbone specimen. Unfortunately, the extensometer malfunctioned, and no strain data was recorded. The test was otherwise normal, and the load cell functioned fine. Which of the following properties could still be accurately obtained from this specimen?

EI (% in 2 inches), sigma ultimate, and hardness

Hooke's law of atoms best explains which of the following properties?

Modulus of elasticity. Hooke's law tells us that the elastic modulus fo steel is really just a measure of the atomic bond strength between two iron atoms (steel is mostly iron, as we will study in part 3). when we heat treat a steel we must be changing the steel's internal structure, otherwise properties like strength and ductility wouldn't change. but we can't change the basic fact that a steel is mostly just abunch of iron atoms stuck to one another, and the strength of the bond between those atoms is not something we can change.

all of the following are "vinyl" polymers except

PET

A rubber band is trained 100% in tension. Over time, the load to maintain that strain decreases.

Stress relaxation

The sad ball at room temperature

Tan delta is at its maximum

A student needs is trying to bend steel tubes for a project. She obtains tubes of four different kinds of steel. Each tube has identical dimensions (radius and wall thickness). She bends all four tubes exactly the same way, but the first three tubes all snap (fracture) during the bending process. She is, however, able to successfully bend the fourth tube. The steel in the fourth tube thus clearly has a larger value of which of these material properties?

Tensile Elongation

Doubling the scratch depth on a fracture of glass fracture toughness specimen would be expected to cause which of the following changes in fracture strength? (Assume Y is constant)

The fracture stress will be about 71% of the previous value

Tensile specimens of Steel X are tested, and the average yield strength of the steel is obtained. other specimens of the same steel are then heat treated, and the yield strength is measured again. All of the following would be necessary in order to determine if the heat treatment significantly strengthened the steel except:

The maximum and minimum tested values of yield strength for the two conditions

The pearlite equation allows the estimation of the carbon content of a slow cooled plain carbon steel with <+ w/o C. Knowledge of the following would allow you to correctly apply the equation?

The total amount of austenite present just above the eutectoid T.

245 degrees C the sample begins to turn clear again, becoming quite transparent by about 260 degrees c

Thermodynamic melting

a translucent sample turns clear on the "cooking" plate

Thermodynamic melting

The AR condition was not significantly different in fracture strength from COM.

This shows that loading in compression is not as affected by defects on the surface.

Annealing the AR glass resulted in a significant increase in fracture strength.

Thus the AR glass was probably NOT tempered. It would have had bad residual stresses that then got "cooked" out in the annealing process.

a dogbone of a typical ductile metal is stressed in tension to a stress of 50 ksi. The corresponding strain is 0.5%. The elastic modulus of the material is 10 Msi. If the specimen is unloaded from 50 ksi stress to zero, what is the strain?

Zero

The elastomer used to make rubber bands features

a relatively low density of cross-links

All of the following demonstrate essentially the same phenomenon excpet:

a round ball of silly putty gradually flowing out into a puddle on the table (frequency dependent)

The DTUL for a polymer is 125 degrees C, while its Tg is 82 degrees C. The polymer is most likely

a semicrystalline thermoplastic

An unknown polymer burns freely when ignited, has a Tg of 80 degrees C and cannot be reshaped upon heating. This polymer is

a thermoset

Injection molded components are known for all the following except:

ability to mold parts with thickness of 1/2" or more

Brittle materials, such as glass, tend to fracture at stresses well below their theoretical maximum strengths because they

are very sensitive to the presence of the microscopic defects

Metals, Polymers, and ceramics are classified that way because of differences in their

atomic bonding

155 degrees C the sample turns white and becomes quite hard to the touch of tweezers

crystallization

Compared to polymers and ceramics, metals typically are

dense and good conductors

All steels have approximately the same

density and density

All steels have approximately the same

density and elastic modulus

All of the following are reasons for the success of components made from polymers (as compared to similar parts made from metals) except:

dimensional stability at elevated temperatures

Pearlite is mostly

ferrite

The average fracture strength of the COM glass specimens(scratch in compression) was not significantly different from that of the AR glass. This is because

flaws in compression have little effect on the strength of a brittle material like glass

Which of the following best explains the large amount of scatter found for the ACID slides in the fracture of glass lab?

for extremely shallow flaws, very small changes in flaw depth result in huge changes in fracture stress, as predicted by fracture mechanics

A ball of silly putty bounces normally, but flows into a puddle when set on the table

frequency dependence of the elastic modulus

A steel with a high carbon equivalent will have a

high max hardness and or a high hardenability

A steel with a high carbon equivalent will have

high potential to form martensite in the HAZ

X- ray diffraction identifies crystalline materials by measuring their

interplanar spacings

Which of the graphs below shows the most likely relationship between the strength and ductility of a typical cold-worked alloy

inverse relationship as the ductility increases the strength decreases

275 degrees C long fibers are drawn from the sample

melt state

a rubber band is stretched and chilled in liquid nitrogen. It then shrinks as it warms up

molecular relaxation at Tg

the sad ball becomes "happy" when warmed in boiling water

rubbery behavior

A 65Cu-35Ni alloy is or can be strengthened by all of the following except:

second phase strengthening

Which of the following classes of polymers generally have "useful mechanical properties" above the glass transition temperature?

semicrystalline thermoplastics and elastomers

Which of the following usually increases with a decrease in average grain size?

sigma ultimate

Which of the following usually increases with increasing cold work?

sigma ultimate (ultimate strength)

Nails are sometimes made from 1010 steel. The primary strengthening mechanism in such a nail is

strain hardening (cold worked)

Steel sheet is to be used in a metal stamping process to produce a car fender. Which one property would be most useful in determining if a given type of steel could be used to successfully produce the part?

tensile elongation

Which of the following is not a good example of anisotropy in material properties

the density of a carbon fiber composite

Polymer fibers usually have elastic modulus values many times as high as the samme polymer in say, an injection modled part. This is because

the molecules in the fibers tend to be aligned along the length of the fiber

The onset (beginning) of dislocation motion in a typical ductile metal is best predicted by

the offset yield strength

The glass transition temperature in an amorphous thermoplastic is the temperature at which

the ratio of loss modulus to storage modulus is a maximum

A new type of glass is being considered for use in the fracture of glass lab next year. the Kic of the new glass is twice as large as that of the old glass. For the scratch in tension condition, we would thus expect the average fracture of stress to be about_____, asssuming the same scratch depth.

twice as large