SE2Lab3.pdf

8/14/2019 SE2Lab3.pdf

1/3

SE 2 Structural Materials

Laboratory Exercise 3Tensile Testing

BackgroundThe tensile test of materials is done to obtain the stiffness (Youngs Modulus), yield

strength(y)( if appropriate to the type of material), ultimate strength at failure(u) and ultimate

strain (u) under the action of tensile loads. From the recorded values of load, deformation, and

specific dimensions of the specimen, one can easily obtain the relationship between stress and

strain. As discussed in class stress can be classified as either engineering stress or true stress.

The engineering stress (= P/Ao) just takes into account the initial cross-sectional area Aoand

ignores the reduction in cross-sectional area resulting from deformation as the applied load isincreased. True stress accounts for the change in the cross-sectional area of the specimen and

usually gives higher stress levels especially in the post-yield stage. Strain is defined as a ratio of

change in dimension to the initial dimension (gage length, in the case of this experiment) of the

specimen.

ObjectiveThe objective of this lab exercise is to observe and analyze the tensile behavior of a number ofcommon materials materials (coupons).

PART 1Each group is assigned 3 coupons belonging to the primary material classes of metal, natural

composite (wood) and polymer, as listed in the attached table. Within each class there are somevariations as below:

a. Polymers Nylon Delrin

b. Wood Oak Maple

c. Steel

non-heat-treated (1018)

heat-treated (1018HT, i.e. heated to 850C for 1.5 hours)

Procedure1. Each team is expected to use only those coupons specifically assigned to it. (See Table 1

below). Measure it and obtain the cross-sectional area and initial gage length.2. Place it into the tensile-testing machine, as instructed. Be careful with the wood coupons,

they are very fragile.

3. Adjust the dial indicator to allow as much travel as possible.4. Initialize the tensile-testing machine (Tare switch)5. Zero the dial indicator.6. One team member will apply the load via the hand crank.

8/14/2019 SE2Lab3.pdf

2/3

7. One team member will call out the displacement increment (0.002" for wood, 0.05" forNylon, 0.010 for Delrin, 0.005 for steel)

8. The load and displacement are recorded.9. Continue until the coupon has failed.10.Record the Peak load.

PART 2(Virtual Lab)Each group will select at least three (3) materials different from the ones assigned in Part 1to test

using the virtual simulator following directions provided in the actual laboratory. All of the data

will be combined into one group report.

ProcedureThese experiments can be conducted in the UC409 Computer lab or from any networked

computer that has internet access. You can even do these experiments from home, however a

fast connection (cable or DSL) is recommended because a video using Real Player is required.You can download Real Player for free at www.real.com

Testing Procedure:1. Go to the URL, http://vlab.ucsd.edu2. Under the test type, choose coupon type.3. Under the material type, choose a material.4. Click Start.5. After the video stops and all the data are recorded, download the data and save it.

Getting Help and Info:

Use the Help and the Info buttons for more guidance in performing this lab.

Final Report Format

Your report should contain the followinga. Objective of the reportb. Description of the materials testedc. Tabulated data of initial dimensions of the specimensd. Tabulated data directly obtained from the experimente. Graph

1. Load vs. Deflection (directly from experiment)2. Stress vs. Strain (calculated)

f. Classification of the materials testedg. Comparison of the results

1. Yield strength, if appropriate2. Ultimate (failure) strength3. Stiffness (Youngs Modulus)4. Ultimate Strain, if appropriate

h. Summary1. Generally compare and contrast all the specimens and their test results.2. For steel testing, compare and contrast the behaviors of heat treated and non-

heat treated steel

8/14/2019 SE2Lab3.pdf

3/3

3. Metals usually exhibit ductile characteristic that other brittle materials dontpossess. Discuss the evidence of this from your observations in the lab.

Section Team Experiment Material Assigned

Steel Wood Polymer

A01 1 Tension 1018 HT Oak Delrin

2 1018 Maple Delrin

3 1018 HT Maple Nylon

4 1018 Maple Nylon

A02 5 1018 HT Oak Delrin

6 1018 Maple Delrin


8 1018 Maple Nylon


10 1018 Maple Delrin


12 1018 Maple Nylon




16 1018 Maple Nylon




20 1018 Maple Nylon




24 1018 Maple Nylon




28 1018 Maple Nylon




32 1018 Maple Nylon

Table 1

SE2Lab3.pdf

Documents

Transcript of SE2Lab3.pdf