HW Questions for Exam 1

In the history of humankind, why did humans work with bronze (the Bronze Age) prior to working with iron (the Iron Age)?

Bronze's lower melting temperature makes it easier to process than iron.

Which of the following is/are example(s) of optical properties of materials?

Refractive Index Reflectivity

The area under the linear portion of stress-strain curve represents

The modulus of resilience

A thin, translucent plastic sheet appears blue in color. Based on this description, which of the following explanations may explain its appearance?

The plastic reflects blue light. The plastic transmits blue light.

A material will thermalize (i.e. reach thermal equilibrium) most quickly when :

thermal conductivity is high and heat capacity is low

How could you improve a plastic's resistance to UV degradation?

- Adding a UV absorbing coating to the plastic's surface. - Including additives to the plastic's composition that help prevent UV degradation.

What contributes to the activation energy (EA) of the mass diffusion coefficient (D)?

- Bond breakage to move the atom from one position to the next. - Bond strains associated with "pushing" atoms out of the way as an atom diffuses from one site to the next.

The elastic modulus of a material...

- is the proportionality constant in Hooke's Law - is the slope of the linear portion of a stress-strain curve

Machining a plastic plate to make it thinner would potentially...

...change its performance parameter(s) for some applications but not alter its material properties.

If a material is crystalline,...

...it has atoms in an ordered arrangement.

Erbium is relatively expensive because...

...it is rarely found in concentrated mineral deposits and must be collected as an impurity from other mining processes.

Polishing the surface of a material so that it becomes really reflective (i.e., a "mirror-like" finish) is an example of...

...modifying the shape of a material in a way that may change its performance for a given application.

A 1 cm thick piece of stainless steel metal is measured to reflect 98% of visible light at a wavelength of 500 nm. How much light is absorbed by the metal at a wavelength of 500 nm?

2%

If diffusivity of carbon into steel at the carburization temperature of 900 °C is 1 x 10-10 m2/s and carburization is undertaken for 400 s, what is a good estimate for the average distance the carbon has diffused into the steel?

200 microns

Consider a copper rod that is 3.14 meters long, 2 cm in diameter, and has an electrical resistivity of 5x10-6 ohm-cm. What is the electrical resistance of the rod?

5x10-4 ohm

A ceramic rod that is 10 cm long has a thermal expansion coefficient of 8 x 10-5 (m m-1 °C-1). What percent strain elongation does the rod undergo when it undergoes a temperature increase of 1000°C? (Remember to multiply strain by 100% to get PERCENT strain.)

8% strain

Using a UV/Vis spectrometer, it is found that a 0.5 cm thick piece of window glass reflects 12% of visible light (at 500 nm wavelength) and absorbs 4% of visible light (at 500 nm wavelength). How much light is transmitted through this glass at 500 nm wavelength?

84%

Thermogravimetric analysis (TGA) is an analytical technique that tracks the mass change of a material as it is heated from room temperature to some higher temperature. TGA can be performed in a variety of atmospheres including air, vacuum, or pure nitrogen. TGA could be used to assess the service temperature of a material for which of the following cases: A. The temperature at which oxidative corrosion occurs for a metal alloy. B. The melting temperature of the material. C. The temperature at which a polymer "softens" and loses its ability to mechanically sustain a load.

A

If a material is deformed plastically, which of the following must be true?

A permanent deformation occurs.

You are hired by a composites manufacturer to help improve the mechanical properties of their fiberglass product. What strategies could be used to alter the mechanical properties of the composite?

A. Apply different chemical treatments to the glass fibers' surfaces prior to embedding them in the polymer matrix. B. Exploring new geometrical arrangements of the glass fibers in the composite. C. Varying the length of the glass fibers used in the composite. D. Varying the composition of the polymer matrix material.

Anodization of aluminum can be used to:

A. Make the surface of the aluminum harder. B. Change the color of aluminum. C. Protect the aluminum against corrosion.

Which of the following factors can contribute to the price of a material?

A. Terrestrial abundance of the elements in that material. B. Whether or not the elements of the material are found in concentrated quantities in ores or only as impurities in ores. C. Commerical/Industrial demand for the elements in that material. D. Speculation by investors in raw elements used to make a given material.

Which of these elements is/are known to form self-limiting oxide surface layers that are protective against further corrosion:

Aluminum Chromium

Why did tellurium prices begin to decrease sharply around 2012?

Because China opened up new, large tellurium mining facilities, flooding the market with more tellurium.

When an object is intended to be deployed deep into the ocean's depths, which of the following materials constants would you use to help determine the amount of elastic compression it will experience?

Bulk Modulus

The dissolution of a polymer into a solvent (solubility) is considered what type of material property?

Chemical Property

A metal rod with a square cross-section has a resistance of 10 ohms. If the square edge has a width of 1 cm and the rod has a length of 10 cm, what is the resistivity of the metal?

Correct answer: 1 ohm-cm

The window panes found in a typical U.S. residential home are a good example of what class of material?

Correct answer: A ceramic-based glass

If you were asked to design a new rubber band that could stretch farther without breaking, which of these material properties would you try to maximize?

Ductility (Strain at Break)

What is the inverse of electrical resistivity?

Electrical conductivity

describe "anodization" of an aluminum part:

Electrochemically oxidizing the aluminum in a controlled manner.

A material with high yield strength and low ductility would be considered "tough"

False

If a material is plastically deformed, this deformation is reversible by removing the load.

False

Most of the materials we use in engineering applications today were developed before the year 1900.

False

T/F: No more indium is available in the earth's crust and so can no longer be mined terrestrially; the only source for indium is through reclamation from old components (e.g., indium solders and flat panel displays).

False

True / False: Paramagnetic materials make good permanent magnets because they can achieve high magnetizations when placed in a magnetic field.

False

True or False: As long as a component's operation temperature remains below the melting temperature for ALL materials in that component, it will not fail.

False

If you wanted to MAXIMIZE the deflection of a bimetallic strip undergoing a temperature swing of 10 °C what type of materials would you choose?

Greatest difference in thermal expansion coefficient (CTE)

If you were asked to design a windshield that would resist being scratched by debris while driving, which material property would you try to maximize?

Hardness

A good dielectric material designed for use in a capacitor should:

Have a high dielectric constant and be a good electrical insulator

Which of the following properties is an example of a THERMAL property

Heat Capacity

You are asked to design a skillet (pan) for cooking. The key requirement is that the skillet reaches the same temperature as the heat source (oven burner) as quickly as possible. Based on this requirement, which of the following materials would you select?

High thermal conductivity, Low heat capacity

Which of the following is an example of a III-V semiconductor?

Indium phosphide

You work for a manufacturing facility that produces electrical resistors. Currently you sell a resistor that has a length of 9 cm, a cross-sectional area of 3 cm2 and uses Metal A with an electrical resistivity of 2 ohm-cm. Unfortunately the melting point of the resistive metal is too low and these resistors keep failing due to melting in operation. You are asked to design a new resistor with the same resistance using Metal B which has a higher melting temperature. Metal B has an electrical resistivity of 6 ohm-cm. What would you recommend for its design?

Length = 1 cm; Cross-sectional Area = 1 cm2

Which of the following best describes the main theme of the materials science and engineering discipline?

MSE seeks to understand and apply the inter-relationships between how materials are processed, their structure, and their resultant properties.

What is mass diffusion

Mass diffusion involves locally random motion of atoms that leads to global mass transport from areas of high concentration to areas of low concentration.

Which of the materials listed below would you select for the submarine's sonar detection panel and why?

Material B because it has the smallest acoustic impedance mismatch with water and will transmit the most sound.

You are designing a system based on piezoelectric actuation to precisely move objects at the nanometer scale. Your system is limited to an operating voltage of 500 V. The system must be able to move objects AT LEAST 150 nm. You are allowed to select amongst the following piezoelectric materials in the table below to accomplish this mechanical motion. Which of these materials would you recommend for this mechanical manipulation system? Material I: d33 = 800 pm/V Material II: d33 = 300 pm/V Material III: d33 = 200 pm/V Material IV: d33 = 100 pm/V

Materials I and II

You work at a cardboard box making company, and the formulation chemist has created a new pulp for making the cardboard used in the boxes. The pulp is cheaper, but when it is made into a standard cardboard box, the box permanently bends under much less weight than the prior pulp formulation. Assuming your boxes still needs to meet the same weight specifications as the previous pulp formulation, what would you do to determine if you could still save money?

Measure the yield strength of the new cardboard, and then using the appropriate deformable bodies formulas, determine how much thicker the cardboard must be made. If the cost for using more of this cheaper pulp in the thicker boxes is still lower than the cost of using less of the more expensive pulp in the thinner boxes, then money can be saved.

Is Dielectric Strength a mechanical property of a material?

No

The Kerr effect is a phenomenon in which the refractive index of a material changes with the application of an electric field. Thus, the Kerr constant (which is the materials property that determines how much refractive index changes with applied electric field) is an example of a material constant that crosses which two classes of properties?

Optical and Electrical

Because it is winter time, the temperature indoors is about 28 °C while the temperature outdoors is about -5 °C. What would you do to improve chances for the helium balloons to still be floating at the party tomorrow afternoon?

Place the balloons outside because diffusivity varies exponentially with temperature and the colder temperatures should reduce the helium diffusion rate.

This material likely has an atomic structure that resembles a "mess of spaghetti":

Polyethylene terephthalate (PET) in soda bottles

When light enters a material and changes its direction of propagation, this process is called:

Refraction

A silicon wafer used in microelectronics processing is an example of what class of material?

Semiconductor

Which of the following is a ceramic? Alnico Silicon dioxide Plexiglas Rubber Cermets

Silicon dioxide

You are designing props for a "western" movie. In the bar fight scene, one of the actresses must break a beer bottle over the head of an actor. Which of the material property(ies) for the bottle listed below is most important to get the scene correct without hurting the actor?

The bottle material should have low toughness.

The polarization of light is defined by:

The direction of the electric field vector

Prisms are capable of separating white light into separate colors because:

The material used is dispersive. The prism has a specific shape

An iron nut and bolt are used to attach two zinc plates together on the underside of a boat. If this boat is to be used in the ocean, what might happen?

The zinc plate will undergo galvanic corrosion.

The total area under the stress-strain curve represents the

Toughness

T/F: Elements with standard reduction potentials lower (more negative) than water are susceptible to corrosion in aqueous environments, even when not in contact with another metal.

True

T/F: In an electromagnetic wave of light, the electric field vector MUST BE perpendicular to both the magnetic field vector AND the direction of wave propagation.

True

Tough materials CANNOT be brittle

True

Assume you are working on constructing a new building in a nominally hot climate that experience a lot of sunshine (e.g., Arizona). To reduce building heating during the day, which color paint would you recommend for painting the roof and why?

White because it reflects the most visible light.

your colleague says he checked the compositions and the new steel beams are identical in composition to the old steel beams. Based on the identical composition, he concludes that these new beams should have the same mechanical properties and that construction should continue. What would be your response?

You would disagree and say that work should stop until you can confirm exact specifications because a material's properties can depend upon other structural features besides composition.

Steel panels to be used in the interior of an oven are going to be electroplated with a corrosion-protection coating. Steel has a thermal expansion coefficient (α) of 4 ppm/°C. Which of the following coating materials would you select to minimize risk of thermal delamination of the coating?

coating with the closest thermal expansion coefficient

If you want to make a firm mattress, should elastic modulus be high or low?

high

Which is NOT a common property of polymers:

high service temperature

The stiffness of a material...

is the proportionality constant in Hooke's Law

Which of these are appropriate units for mass diffusivity?

m2/s