Lab Writeup Guidance
Prepare your shared data sheets with names from all 6 people. This should be as an electronic
document so that each group can have a copy. Turn in a printed copy in the plain folder
marked Shared Data Sheets when the color coded homework folders are circulated on
Thursday TOMORROW. What should be there?
Load vs Displacement data for the mechanical tests of the 1010 annealed steel, including tensile
test data for both 700 and 900 degree annealed samples, along with dimension measured for
thickness, width, and gage length. In your lab reports, mark the slope of the initial linear region
and discuss why you don't expect this to agree with the known value of Young's Modulus.
Include the load displacement data of the 700 and 900 degree annealed samples with indications
of the specific load at which the Luders marks were first observed near the hole on each side.
Include an angle of the Luders bands during propagation on the tensile sample for comparison.
There should be data sheets for weights of the samples and the foil pouches that can help you
determine if you can make sense of the weight changes. Clearly now that we have done the
diffusion discussion, you understand that the carbon in the steel might have evaporated if we did
not include the burning toothpicks to consume the oxygen in the pocket and provide CO and
CO2 as a source of surface C in the steel. x=rootDt lets you estimate how deep the effects might
have been. In your reports, you should attempt to determine if all of the carbon left and if it went
in, how much went in and how far in did it go. This data may or may not be useful....use your
engineering judgment but make sure you have the data in the shared data. Your individual
reports will analyze the data obtained from the sample with the circular hole. Take a picture of
the luders strain that starts at the edge of a hole. For the second part of the experiment, include a
data sheet of the superficial hardnesses of the samples to assess if any changes in hardness result
from the electrochemical effects of the battery and the Mg sheet. You should include data on the
voltage-current plot obtained from the battery and from the open circuit voltage and the closed
circuit current caused by the Mg sheet in electrical contact with the spring steel. You will be
asked to discuss why these behave the way they do. Include the load-displacement plots of the
spring steel samples that were used as anode and cathode in the battery driven charging
experiment and that was used as the cathode when coupled to the Mg alloy. Include any photos
you intend to use, particularly those showing the luders markings that develop around the
hardness indentations. You should be able to determine the size of the luders zone relative to the
apparent mark left by the indenter. You should have taken images with the microscope. Next
week, when your group writes up the experiment, you will use this data and include this data as
an appendix to your report.
Looking ahead to the due date for the lab write ups...that is Labs #1 are due Next Thursday,
October 24. What to include in the Lab write up.--this lab write up is to be modeled after a
technical report for a company. Thus, it is NOT A TERM PAPER where you would describe
your entire known knowledge with a substantial background section. Rather each of these two
experiments is unique and represents the type of experiment you might perform as a working
engineer to accomplish some purpose at your place of employment. The technical report then
documents the outcome. In the spirit of YOU ARE THE ENGINEER, create a scenario where
your supervisor has asked you to look into something....or even better, you have taken the
initiative to learn more about the particular systems your company makes or that you are
planning on using in an upcoming design. I have created the lab to provide learning
opportunities. In writing it up, pretend that this is a project you have initiated and actively
integrate the knowledge you have accumulated from all of your courses and life experience.
This is likely to be the first corporate technical report you write so it will form a template for
how you write up these types of documents. I will suggest some formats below. Keep it short so
that it will actually be read by others and will inform them. It is intended to record the outcome
for others in your company that follow you so they will not need to redo the experiment. They
can just read what you have done and reported.
Now because this lab is really two topics glued together, I believe it will be easier to write two
shorter reports that are modeled on a technical report for a company rather than
mixing the topics. In planning for this experiment, I began experiments this summer thinking
that I could overdrive the hydrogen embrittlement and MAKE the annealed steel samples
embrittle so that the samples of the same geometry could be made to fail at very low stresses, but
found that these samples were impervious to hydrogen embrittlement. That is so important I
want to repeat it because there is a chance in the years ahead you will be designing structures to
deal with hydrogen as a fuel, if the hydrogen economy becomes a reality. SOFT STEEL IS NOT
EMBRITTLED BY HYDROGEN so it would probably be the favored material to contain
hydrogen, covered, perhaps, by some coating that might slow down diffusion. But I also want
you to know about embrittlement for the same reason. Hence, to show the embrittlement
phenomena and let you experience it first hand, it was necessary to find a high strength steel
where embrittlement rears its ugly head. I used the same general sample size so the grip set up
would work and, as you have noticed, produced a situation where there were NO LUDERS
strains in the spring steel. It would be only natural for you to notice the similar sample sizes and
shapes with very different outcomes. Once the little region near the stress concentration fails at
relatively low ductility, the geometry is (or soon becomes) cracklike, introducing huge stress
concentrations, forcing the material to fracture without much local yielding. You will notice
alternating shear lips as the material yields through its thickness. This type of failure is
characteristic of thin sheet failure. You would not see this by testing round tensile bars.
Your report(S) each should have:
Title page with authors, contact information as of the date of writing, date, and an executive
summary
Objective/Background. Why you are doing this....in the spirit of what the experiment is
designed to show and why it is useful enough to spend time and $
Experimental Protocol or Procedure.....the what you did part in enough detail to allow others to
reproduce your work
Results. The facts that were determined (notice how the results and discussion separate FACTS
from THINKING ABOUT THE FACTS which belongs in the discussion)
Discussion. Interpretation of the facts that may include assumptions. The meaning of the results
in the circumstances at hand. The IMPLICATIONS of the results is the most important part and
you should strive to actively state them.
Conclusions.
Figures
Appendices
The Luders band experiment lets you answer the question: Can stress concentrations be used to
estimate the yield load of engineering structures. How, and with what accuracy? Can this
experimental method be used to convince management about the reality of the effects of stress
concentrations. That is stress concentrations actually reduce the failure loads of engineering
structures so that drilling a hole can drop the strength of a tension member all by itself.
The hydrogen charging experiment lets you answer the question: Does the electrochemical
creation of nascent hydrogen on hardened steel modify the mechanical properties of the steel?
Can we determine if the steel strength is reduced, or is the ductility reduced, or both? Hardness
can help you answer this. What precautions must be taken when designing system that utilize
high strength steel? Can this be used to convince any non-believers in the engineering team
about the importance of hydrogen effects on high strength steels.
The goal of having you write this engineering technical report style of write up is to give you a
little real world experience. Remember that you are forming a template for yourself in how you
will write up your engineering findings.