Department of Mechanical Engineering
ME 215 - Structure and Properties of
Materials
Laboratory Manual
Spring, 2004
Professor A. Plumtree
Room E2-2312
Lab Supervisor:
Norval Wilhelm
Teaching Assistants:
Karen Howard E3-2119A x3499 khoward@engmail
Shahzma Jaffer E3-2106G x2319 sjaffera@engmail
Amir Poursaee E3-3101D x6108 aesmaeil@engmail
Place: Materials Laboratory (E3 2119)
Time: Tuesdays 2:30-5:30pm
Thursdays 2:30-5:30pm
Project: Elastic Bending of Cantilever Beams
Laboratory Experiments:
1.
2.
3.
4.
5.
6.
7.
8.
Crystallography
Microscopy & Surface Defects
Rolling
Cold Working
Annealing
Polymers
Impact
Magnetism (Possibly)
Crystallography
Purpose:
To gain an understanding of the different unit cells and material structures.
Apparatus:
1) Unit Cell Models
2) Ping Pong Ball Models
3) Molecular Models
4) IMSE Software
Procedure A (Using Models):
1.
2.
Use the aluminum base unit cell models to build FCC, BCC and
HCP unit cells. (sketch) Identify the most closely packed planes
and directions. Identify locations where interstitial atoms could
reside in the cubic cells.
Use the ping pong ball models to compare HCP and FCC
structures by changing the stacking sequence of their closest
packed planes of atoms. What is the stacking sequence for each?
(i.e. ABA ABB ABC AAB?)
Procedure B (Using Interactive Software):
1.
Use the IMSE Software to explore unit cells, ceramic structures
and polymer mers from different perspectives. Sketch at least one
ceramic, polyethelyne (PE) and polystyrene
2.
Use the IMSE Software exercises and examples to describe
directions and planes. Sketch some of these examples (along with
the appropriate plane or direction).
(Instructions for the software are located beside the computers in the
laboratory.)
Laboratory Report:
This experiment should provide mostly qualitative observations of crystal structures.
Compare the different crystal structures and give example materials for each structure.
How do different crystal/mer structures affect material properties, like density, ductility?
What materials reflect these structures and properties? How can the interstitial sites be
used to affect the strength of a material? (Use an example.) Elaborate on these ideas and
discuss other ideas brought forward by this laboratory investigation.
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Microscopy & Surface Defects
Purpose:
To gain an appreciation of optical microscopy and to use microscopy to
identify crystallographic structures.
Apparatus:
1) Optical microscope
2) Optical microscope with digital camera & computer
4) 1 Iron specimen
5) 1 Brass specimen
6) 1 multiphase specimen
7) several tin specimens
Procedure A (Using Optical Microscope):
1.
2.
3.
4.
5.
Read the instructions for the safe use of your microscope! (THIS
KEEPS THE MICROSCOPE SAFE!!!) Hint: Always start and
finish looking at a specimen using the lowest magnification
objective lens (usually the shortest lens).
Examine all the lenses. Multiply the magnifications of each of the
objective lens by the eyepiece magnification to determine the total
magnification for each objective lens setting. (record these values)
Label all future microscopic sketches with the appropriate
magnification.
Examine the multiphase specimen. Identify the different phases in
the metal. (sketch & label)
Examine the brass specimen. Identify the annealing twins. (sketch
& label)
Tin twins when mechanically deformed – try gently bending (NOT
breaking) the tin and observe what happens.
Procedure B (Using Optical Microscope with Digital Camera):
1.
2.
3.
Read the instructions for the safe use of your microscope! (THIS
KEEPS THE MICROSCOPE SAFE!!!) Hint: Always start and
finish looking at a specimen using the lowest magnification
objective lens (usually the shortest lens).
Examine the iron specimen. Identify the grains and grain
boundaries. (snap an image - sketch & label)
Measure the average ASTM grain size for this sample using the
instructions beside the computer.
2
Laboratory Report:
This experiment should provide mostly qualitative observations of microscopic
structures. Postulate on the influence of different phases in a material. Explain the
different surface defects observed in the experiment, and their influence the strength of
the materials. Which surface defect is the most efficient strengthening mechanism? How
does grain size influence the strength of the material? What might one estimate about the
strength of iron given a K= 0.6 MN m-3/2 and o=55 MPa? Elaborate on these ideas and
discuss other ideas brought forward by this laboratory investigation.
3
Cold Working
Purpose:
To gain an understanding of the effects of cold working in metals.
Apparatus:
1) 1 6061 Aluminum Alloy tensile specimen (previously cold worked by
rolling)
2) 4 fully annealed 1/2 in. Brass cubes (0% CW)
3) Compression rig
4) Houndsfield Tensile rig
5) Hardness testers
6) Calipers
7) Results for As-Received 6061 Aluminum Alloy tensile specimen from
tutorial
Procedure A (Tensile Test):
1.
2"
gauge
length
complete
gauge
length
2.
3.
4.
Measure the cross-sectional area, and the complete gauge length of
the cold-rolled Al alloy tensile specimen.
Mark a gauge length of 2 inches on the tensile specimen with
pencil or marker.
Perform a tensile test on the cold-rolled specimen and plot data.
Measure the elongation of the specimen by holding it together and
measuring the new distance between the gauge length marks.
Procedure B (Hardness Tests):
Hint: put your data in a table!
1.
Sand off a top and bottom of all brass specimens to remove any
scale or oxidation caused by the annealing process.
2.
Measure the heights of 3 of the brass specimens
3.
Cold work these 3 brass specimens by 10000, 20000 and 30000 lbs
using the compression rig. (The compression rig must be run with
the assistance of the technician/TA)
4.
Measure the new heights of these 3 Brass specimens
5.
Measure the Rockwell B hardness of all 4 brass specimens. Take
3-4 measurements for each and calculate an average.
6.
Measure the Rockwell T hardness of the tensile specimen. Take 34 measurements and calculate an average. (Take these in the grip
end - not in the gauge length.)
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Laboratory Report:
Results:
Convert the load-displacement plot to a stress-strain plot given the cross sectional area
and complete gauge length of the specimen. Label important features on the stress-strain
curve and glue/staple this plot into your lab book. Plot one graph representing % Cold
Work versus Tensile Strength (UTS) and % Elongation using both the right and left Yaxes. (Include the results of the tensile test for 6061 as-received aluminum from the
tutorial.) Plot two graphs of % Cold Work versus Hardness: one for the aluminum and
one for the brass.
For rolled specimen: % CW, as in Eqn. 7.2 OR Solution to Example 7.1
For compressed specimen: % CW = 100% x (ho - hf)/ho
Discussion:
Explain the trends seen in the graphs in the Results section. Explain what is happening in
metals during cold working (strain hardening).
Do you think that the as-received aluminum alloy tensile specimen came from a truly 0%
cold-worked state? Why? What are the implications of this idea?
Estimate the strain hardening coefficients for Aluminum and Brass (Cu-Zn), (see table in
Askeland). How do these values relate to a material's ability to be cold worked? Explain
how these values could be obtained experimentally and how they would differ for BCC
and HCP materials.
Elaborate on these ideas and discuss other ideas brought forward by this laboratory
investigation. Make sure to discuss the accuracy of the results and comment on possible
sources of error. (One hint: Compare percent elongation at failure using both the graph
and the 2 inch gauge length.)
5
Annealing
Purpose:
To discover the effects of the annealing process.
Apparatus:
1) 1 Annealed 6061 Aluminum Alloy tensile specimen (440°C for 3 hrs.)
2) 4 Brass cube specimens annealed at 100°C, 300°C, 400°C and 600°C
respectively for 1/2 hour and air-cooled
3) Houndsfield Tensile rig
4) Rockwell Hardness Testers
5) Results for Aluminum Alloy tensile specimens from tutorial & cold
working experiment
Procedure A (Tensile Test):
5.
2"
gauge
length
complete
gauge
length
6.
7.
8.
Measure the cross-sectional area, and the complete gauge length of
the annealed Al alloy tensile specimen.
Mark a gauge length of 2 inches on the tensile specimen with
pencil or marker.
Perform a tensile test on the annealed specimen.
Measure the elongation of the specimen by holding it together and
measuring the new distance between the gauge length marks.
Procedure B (Hardness Tests):
Hint: put your data in a table!
7.
Lightly sand off the top and bottom of all brass specimens to
remove any scale or oxidation caused by the annealing process.
8.
Measure the Rockwell B hardness of all 4 brass specimens. Take
3-4 measurements for each and calculate an average.
9.
Measure the Rockwell T hardness of the tensile specimen. Take 34 measurements and calculate an average. (Take these in the grip
end - not in the gauge length.)
Laboratory Report:
Results:
Convert the load-displacement plot to a stress-strain plot given the cross sectional area
and complete gauge length of the specimen. Label important features on the stress-strain
curve and glue/staple this plot into your lab book. Plot one graph representing
Annealing Temperature versus Tensile Strength (UTS) and % Elongation (from the 2"
gauge length) for the aluminum alloy specimens (tutorial and this lab) using both the
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right and left Y-axes. (Assume that the aluminum alloy specimen from the tutorial was
annealed at 50°C.) Plot two graphs of Annealing Temperature versus Hardness: one for
the aluminum alloy and one for the brass.
Discussion:
Explain the trends observed on the graphs in the Results section, based on the different
stages of annealing. In your explanation, include sketches and a description of the
microstructural changes occurring during each stage of annealing.
How can the effects of annealing be related to the heat-affected zone in a weld?
Using the hardness and tensile strength values for three aluminum alloy specimens (use
values from the tutorial and the Cold Working experiment), plot a graph of UTS vs.
Hardness. Using your graph create an equation correlating the hardness of aluminum to
its tensile strength. Discuss how hardness is related to tensile strength.
Elaborate on these ideas and discuss other ideas brought forward by this laboratory
investigation. Make sure to discuss the accuracy of the results and comment on possible
sources of error.
7
Polymers
Purpose:
To discover the differences between thermoplastics and thermosets.
To discover the effects of temperature and strain rate on polymers.
Apparatus:
1) Epoxy resin & hardener
2) Polyethylene pellets
3) Molds & mold release spray
4) Ovens set at 180°C & 250°C
5) Ice/water bath
6) Hot air blower
7) Silly Putty
8) Elastic band
9) Liquid nitrogen
10) Various tongs and gloves
Procedure A (Thermoset vs. Thermoplastic):
9.
10.
11.
12.
13.
14.
15.
16.
Mix equal parts epoxy resin and hardener. Use about one "dime's"
worth of each.
Spray a mold with mold release. Spoon mixture into the middle of
a mold (it will flow out in the oven).
Put ONE layer of polyethylene pellets into a mold sprayed with
mold release.
Heat the epoxy at 180°C and the polyethylene at 250°C for 10
minutes. (Use gloves/tongs!)
Go on to Procedures B & C while the epoxy is curing and then
come back to complete this section.
Remove specimens from the oven (use gloves/tongs!) and then
cool the polymer specimens in cold water and dry. Note any
interesting observations.
Hold the thermoplastic specimen with tongs and heat with the hot
air blower. When it becomes hot try bending or pulling the
specimen while holding it in front of the hot air. Describe all your
observations! Can you get it to melt?
Repeat step 5 for the epoxy specimen.
Procedure B (Strain Rate):
10.
11.
Take the silly putty and pull it apart as fast as you can! Bounce it
like a ball. Record your observations.
Take the silly putty and pull it apart slowly. Push the silly putty
slowly against a table. Record your observations.
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Procedure C (Temperature):
1.
2.
Take the elastic band out of the liquid nitrogen and pull it or knock
it against the table. (Be careful - the frozen elastic can "burn"
you!) Record your observations.
Once the elastic has warmed to room temperature pull it again.
Record your observations.
Laboratory Report:
Which polymer (polyethylene or epoxy) is a thermoset and which is a thermoplastic?
How do your observations support your statement? Use theory to explain your
observations of the polyethylene and epoxy specimens. Why do they react differently to
the applied heat of the hot air blower?
How does strain-rate effect the apparent strength and ductility of a polymer? Explain this
phenomena.
How does temperature effect the ductility of an elastomer? Would changes in
temperature have the same effect on thermoplastics? Explain why ductility is affected by
temperature. Would you expect strength to change with temperature - why?
Elaborate on these ideas and discuss other ideas brought forward by this laboratory
investigation. Make sure to discuss the accuracy of the results and comment on possible
sources of error.
9
Impact Lab
Purpose:
To gain an understanding of toughness and the ductile to brittle transition
in metals.
Apparatus:
1) 5 AISI-1020 Steel Charpy specimens
2) 3 6061-T6 Aluminum Alloy Charpy specimens annealed at 440°C for 3
hrs & air cooled
3) Charpy impact test rig
4) Furnace and hot plate oven
5) Liquid Nitrogen
6) Ice Bath
7) Dry Ice
8) Stereo Microscope
Procedure A (Charpy Test):
*The Charpy Impact tester must only be used under the supervision of a TA or
technician!
17.
From the following list, choose 2 charpy samples and test these in
the Charpy Impact Tester as directed by the TA. (Note: The
temperature at the root of the notch begins to change as soon as the
sample is removed from the heating or cooling medium. ASTM
standard for the Charpy impact test requires that the delay time in
transferring the specimen and performing the test be less than 5
seconds.)
AISI-1020 Steel at
6061-T6 Aluminum at
18.
19.








120°C (Furnace)
60°C (Oven)
0°C (Ice bath)
-60°C ("Dry ice")
-190°C (Liquid nitrogen)
60°C (Oven)
0°C (Ice bath)
-190°C (Liquid nitrogen)
Record the impact energy absorbed by each specimen.
Share your data with the other three groups.
10
Procedure B (Fracture Surface Examination):
12.
13.
14.
15.
Examine steel and aluminum alloy specimens from each of the
eight charpy tests.
Estimate the amount of ductile and brittle fracture on each
specimen as a percentage of the total fracture surface. (Use the
stereo microscope if needed.)
Sketch and label an example of a fracture surface containing both
brittle and ductile portions.
Sketch magnified (SEM) views of ductile and brittle fracture
surfaces.
Laboratory Report:
Results:
As a part of the Results section, plot the energy absorbed due to impact as a function of
test temperature for all eight steel and aluminum alloy specimens. Also, plot the
percentage of ductile fracture as a function of test temperature for all eight steel and
aluminum alloy specimens. Where appropriate, label the ductile to brittle transition
temperature on both graphs.
Note that the transition temperature can be determined using two methods. First, the
temperature corresponding to the midpoint energy between the ductile and brittle regions
defines transition temperature. The second method defines transition temperature as the
temperature at which the impact produces a half-brittle and half-ductile fracture surface.
Discussion:
Compare the changes in the toughness of the aluminum alloy and the steel with
temperature. Referring to your graphs and fracture surface sketches, explain the
differences in terms of crystal structures and slip systems. Comment on how these
differences would affect your choice of material when designing a structure subjected to
impact at low temperatures.
Some define the transition temperature in steel as the temperature corresponding to a
fixed amount of absorbed impact energy, such as 20 or 27 J. Discuss how well this
method applies to your results by comparing all three methods for determining transition
temperature. Discuss any differences in these results, commenting on the accuracy of the
results and any sources of error.
Elaborate on these ideas and discuss other ideas or errors brought forward by this
laboratory investigation.
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