CityCollege of San Francisco

ENGN 45

Materials Science for Engineers

Laboratory Experiments

Crystallography

Objective:

To become familiar with the basic terminology of crystallography and develop an elementary understanding of the three-dimensional structure of solids.

Procedure:

Part I

  • Build three unit cells common to metals: fcc, bcc and hcp. (Use the hexagonal prism form for hcp.)
  • Study these models and determine the locations of the octahedral and tetrahedral interstitial sites.
  • Submit a professional pictorial drawing (using computer-aided drafting software or drawing instruments) of each of these unit cells. Clearly show the positions of the lattice points for the fcc, bcc and hcp unit cells. Clearly show the octahedral sites and the tetrahedral sites for both the fcc and the bcc unit cells.
  • Answer the following questions:
  1. How many lattice points are in each unit cell? (Clearly state your logic.)
  2. How many octahedral sites are in each unit cell? (Clearly state your logic.)
  3. How many tetrahedral sites are in each unit cell? (Clearly state your logic.)

Part II

  • Build several (minimum of five) close-packed planes and study the stacking sequence variation between the two close-packed crystal structures, fcc and hcp.
  • Submit drawings looking down the stacking direction for each structure.
  • Answer the following questions:
  1. What is the Miller index of the family of close-packed planes in fcc? What is the Miller-Bravais index of the close-packed planes in hcp?
  2. What is the stacking direction in fcc? In hcp?
  3. What is the family of close-packed directions in bcc, fcc and hcp?
  4. In terms of the radius R of spheres on the lattice points, what is the radius r of the largest sphere that would fit into an octahedral site and into a tetrahedral site? (Show your proof clearly.)
  5. What is the angle between the () plane and the () plane?

Safety Issues:

  • Don’t eat the candy (or anything else) in the lab room.
  • Take care not to stick a toothpick in your teammate’s eye.

Work Hardening

or

Strain Hardening

or

Cold Working

Objective:

To determine the effect of cold-working a sample of ETP (electrolytic tough pitch) copper by observing changes in the hardness of the material resulting from increased cold-work.

Procedure:

  • Measure the initial hardness value of a piece of ETP copper barusing the 15T Rockwell hardness scale.
  • Cold roll the copper bar to 5% coldwork and measure the hardness value.
  • Continue cold rolling and taking hardness values in 5% coldwork intervals until 20% coldwork is reached.
  • Cut off and set aside a piece of the 20% coldworked copper.
  • Continue cold rolling and taking hardness values in 10% coldwork intervals until 40% coldwork has been attained.
  • Cut off and set aside a piece the same length as the one set aside at 20% coldwork.
  • Continue cold rolling and taking hardness valuesin 10% coldwork intervals until 60% coldwork has been attained.
  • Clean up and put away all equipment.
  • Plot the hardness as a function of the percent cold work.

Notes:

  • Theremaining piece of copper (60% CW)at the end of the lab should be the same length as the two previously cut pieces (20% CW and 40% CW). You will need to do a calculation to determine the length to cut them. Hint: The volume of the material does not change, nor does the width.
  • The three pieces are to be saved and used to make samples for the Recrystallization experiment to be performed later.

Safety Issues:

  • Wear safety glasses when cutting or sanding the copper.
  • Be cautious when using rolling machine: Do not get hair or fingers near the gears or rollers.
  • Use caution when cutting copper with bolt cutters. No fingers near the blades.

Tensile Test

Objective:

To determine the type of Al from which a standard tensile test specimen is made by obtaining its mechanical properties in a standard tensile test.
The possibilities are:

  • 2024 T3xx Al
  • 6061 T6xx Al
  • 2017 T4xx Al
  • 2011 T3xx Al

Procedure:

  • Mark two points on the Al tensile test specimen and measure this initial gauge length.
  • Measure the initial diameter of the specimen.
  • Perform a standard tensile test on the specimen, recording data of load (force) vs. elongation (length) until the specimen breaks.
  • Record the maximum load obtained in the test.
  • Measure the final diameter of the specimen.
  • Clean and put away all equipment.
  • Normalize your data and plot stress vs. strain, including the maximum load.
  • Obtain the following by calculation or direction inspection of your plot:
  1. Modulus of elasticity (Young’s modulus)
  2. Tensile Strength (T.S.)
  3. 0.2% offset Yield Strength (Y.S.)
  4. reduction-of-area ductility
  5. elongation ductility
  6. true stress at failure
  7. toughness

Safety Issues:

  • Wear safety glasses if you are near the specimen during the test.
  • Use caution with the dividers as the points can be quite sharp.
  • Use caution when hammering the gauge marks on the specimen.
  • Use caution when replacing the fixtures on the machine.
  • Stay away from large threaded columns on the tensile testing machine as the grease will stick to your skin, clothes, etc.

Microstructure Analysis

Objective:

To determine the size of the grains in a metal sample using 3 different methods. The shape of the grains will also be analyzed.

Procedure:

  • Analyze a copy of a photomicrograph of a steel sample that has been ground, polished and etched with 2% nital (2 vol % conc. Nitric acid and 98 vol % ethyl alcohol) to reveal its microstructure.
  • Put away all materials and equipment when finished.
  • Write up your report and make sure to answer the following questions:
  1. Knowing that the micrograph was taken using a 40X objective lens instead of the 10X objective lens called for on the scale reticule, what is the magnification factor, m, of the photomicrograph? (Show the logic of your computation clearly.[1])
  2. What is the average diameter of the grains in your sample? Report your answer in both SI units (millimeters) and English units (inches).
  3. What is the grain density of the grains in your sample? Report your answer as number of grains per unit area. For SI units, use square millimeters for the unit area. For U.S. units, use square inches.
  4. What is the ASTM grain size number for the grains in your sample?
  5. Compare the microstructure of the grains in the micrograph you were given to one of the micrographs in your textbook. (You may choose any one you wish.)
  6. Explain the process of etching and why it is necessary to do it in order to reveal the microstructure of a sample. Include a description of a typical scanning electron microscope (SEM).

Safety Issues:

Use caution with the dividers as the points can be quite sharp.
Concrete

Objectives:

  • To mix a batch concrete that has the best cost/strength ratio.
  • To study the effect of curing time on the compressive strength of Portland cement concrete.
  • To study the effect of the volume ratio of cement:sand:gravel (c:s:g) on the compressive strength of Portland cement concrete.

Procedure:

  • Determine the bulk density and porosity of sand by a volumetric analysis.
  • Determine the bulk density and porosity of gravel by a volumetric analysis.
  • Calculate the ratio of c:s:g for an ideal “zero porosity” mixture of concrete.
  • Choose a ratio for your lab group that is richer than this ideal mixture.
  • Calculate the weights needed of each ingredient (cement, sand and gravel) to mix up a batch of your chosen ratio that will fill a volume of 4 cylinders, 4 inches high and 2 inches in diameter. (Use a bulk density of 94lbs/ft3 for Portland cement.)
  • Weight out each constituent and mix thoroughly.
  • Add just enough water to make the mixture workable. (Add the water in 50ml increments. The mix should have the consistency of cookie dough.) Record the amount of water used and calculate the water/cement ratio.
  • Firmly pack the concrete in 4 cylindrical molds as densely as possible.
  • Store the cylinders in a 100% humidity environment for 2 days.
  • Clean up and put away all equipment.
  • After 2 days, remove the concrete from the molds, wrap each cylinder in wet paper towels and store in zip-lock bags that have at least an inch of water in the bottom.
  • After 1 week from mixing up the batch, cap a concrete cylinder and perform a compression test. Repeat each week for the following 3 weeks.
  • Plot the compressive strength vs. curing time. Compare with graphs found in the literature.
  • Compare your results with groups that used a different ratio.
  • Make sure that your report answers these questions:

1.What were the bulk densities of the materials you used in the concrete you made? Explain how these values were obtained.

2.Distinguish between bulk density and apparent density. Explain why apparent density and true density often are not identical. What was the apparent density of the aggregates you used in your concrete?

3.Distinguish between curing of concrete and drying of concrete. Why is curing essential and drying to be avoided?

4.Why was it necessary to cap the test cylinders before they were tested for compressive strength?

5.Discuss your curve of compressive strength as a function of curing time and compare it to curves found in the literature.

6.In terms of dollars per cubic yard per kilo pound per square inch($/yd3/ksi), what was the cost of your concrete mix?

Safety Issues:

  • Mix the concrete in the small room where there is ventilation.
  • Wear gloves and dust mask when mixing the concrete.
  • Melt the capping compound under the hood. Do not overheat the hot plate.
  • Use extreme caution when capping the concrete samples so as not to drip the compound on the hot plate or anywhere else (including your hands, arms, etc.)
  • Clean up all cement dust and debris using the large yellow garbage can filled with water. Not a speck of dust should go down the drains of the sinks! (This is as much a plumbing issue as a safety issue.)

Recrystallization

Objective:

To explore the effect of coldwork (strain-hardening) on the recrystallization temperature of copper.

Procedure:

  • Cut the 3 pieces of copper bar stock from Lab #4 that you coldworked to 20%, 40% and 60% into 7 samples each.
  • Anneal a sample of each percent of CW for 20 minutes at these temperatures:
    80oC, 160oC, 240oC, 320oC and 400oC.
  • Measure hardness values for all samples using the 15T Rockwell hardness scale.
  • Plot three curves (on the same graph) of hardness (y-axis) vs. annealing temperature (x-axis) for each percentage of CW.
  • Select appropriate temperatures for the remaining two samples of each percentage of CW and refine your plots.
  • Clean up and put away all equipment.
  • Label the recrystallization temperatures for each percentage of CW on your graph.
  • Make sure that your report answers these questions:
  1. Explain why a range of recrystallization temperatures is given in the Metals Handbook for ETP copper.
  2. Why did the heavily coldworked copper recrystallize at the lowest annealling temperature?
  3. Explain what is meant by grain refinement.
  4. In the context of this experiment and of the discussion of recrystallization in your text, what is meant by nucleation?

Safety Issues:

  • Use caution when cutting copper with bolt cutters. No fingers near the blades.
  • Use caution when taking hot pieces of copper out of the ovens.

Thermal Analsysis
(Cooling Curve)

Objective:
To determine the composition of an unknown Pb/Sn alloy by the process of thermal analysis, i.e. slowly cooling the alloy (isothermally) from the molten state and tracking the temperature as a function of time.

Procedure:

  • Set up all equipment. Be sure that the heat sink is soaked at the appropriate temperature.
  • Note whether the unknown Pb/Sn alloy sample given to you by your instructor is hypereutectic or hypoeutectic.
  • Melt the Pb/Sn alloy in a test tube over a Bunsen burner and place in the heat sink with a thermocouple.
  • Using the thermocouple, record the temperature of the alloy every 30 seconds, until the sample is cooled below the eutectic thermal plateau.
  • Re-melt the alloy (from the top of the test tube) and return the sample to the instructor.
  • Clean up and put away all equipment and materials.
  • Plot a cooling curve of your data.
  • From the thermal arrest temperatures of the alloy, determine the composition.
  • Make sure that your report addresses these questions:
  1. What is the theory behind how a thermocouple measures temperature?
  2. How does the cooling curve relate to the Pb/Sn equilibrium phase diagram?
  3. Why was it necessary to see the eutectic thermal plateau in this experiment?
  4. What is super cooling? Did you see evidence of it during your experimentation? If so, point out where on the cooling curve.
  5. What was your sample number? What was its composition (weight %)?

Safety Issues:

  • Keep space around the Bunsen burner clear.Tie hair back and be sure that you do not have loose sleeves or other clothing that may get in the way of the flame.
  • Melt the alloy only after everything is set up and ready. Never leave the burner unattended. Be sure to turn it off when finished.
  • Use extreme caution when transporting the heat sink from the furnace to the ring stand. Make a LOUD announcement to the entire class before you proceed.
  • Use extreme caution when re-melting the alloy to remove the thermocouple. Melt from the top down and be very very gentle in your handling. DO NOT BREAK THE TEST TUBE.
  • Put the hot heat sink back in to the (turned off) furnace so that no one inadvertently touches is before it is cool.

Jominy End-Quench Test

(Hardenability)

Objective:

To perform a standard Jominy end-quench test and obtainthe hardenability curve for an unknown steel sample. To determine the type of steel that the sample is made from.

The possibilities are: 1040 steel, 4140 steel, 4340 steel.

Procedure:

  • Austenize the standard Jominy end-quench test sample.
  • Place the sample in the Jominy fixture and spray the end with water at standard conditions for the test.
  • After sample is cool, file 3 flat lines along the axis of the cylinder.
  • Using the RA hardness scale, take hardness readings at 1/8 inch intervals from the quenched end along the flat lines.
  • Clean up and put away all equipment.
  • Plot the hardenability curve for the steel.
  • Compare the curve with those found in the literature. Determine the type of steel from which the sample was made.
  • Make sure that your report answer these questions:
  1. What is the definition of hardness?
  2. What is the definition hardenability?
  3. Compare and contrast hardness and hardenability.
  4. Why is hardenability an important property of steel?
  5. What does the “40” in the designation “1040 steel” refer to?

Safety Issues:

  • Use extreme caution when transporting the Jominy sample from the furnace to the Jominy fixture. Make a LOUD announcement to the entire class before you proceed.

Materials Laboratory Project

The final lab is one of your own design on a material of your own selection. One type of project is to examine the effect that changing one parameter has on a property of the material. For example, you might examine how resistivity changes as a function of plastic deformation in a metal. Other types of projects might include testing products of various commercial materials or figuring out some of the equipment in the lab.

You must present your project proposal to the instructor by the end of the third round of experiments of the semester. You must clearly state the objective of the project, the materials and equipment needed, and where you intend to obtain these needed items. (You may use anything in the Materials Lab; however, you are responsible for obtaining any material or equipment that the Lab does not have.) The proposal must be made in the form of a business letter addressed to your laboratory instructor and signed by all of the members of the group.

The experimentation may be started any time after the proposal has been approved. An oral presentation (by all of the participants in the group) is due in the last Lab session.

Lab Reports

All lab reports should be submitted on time and with a professional format. How they lookis as important as the content they provide. They should be clear, concise and complete. Keep them as short as possible - less is more! The following provides an outline for your lab reports.

Title Page

  • Lab group designation (A1, A2, B1, B2, C1 or C2)
  • Name of lab team/consulting company
  • Name of the lab experiment
  • Class and Semester
  • All team member names (full names spelled correctly) with their assigned class numbers in front of their name.

Objective

This is a very short statement addredsssing the purpose of the lab.

Background Theory
You should include enough information here so that a layperson would be able to understand the report. Your audience is your client, not your teacher. Think of yourself before you enrolled in this course. Include everything that you would need to know in order to understand what the experiment is about.