# Tensile Test

Test Objectives:        To determine the tensile strength and load-deformation characteristics of the supplied specimens.

Equipment:       Universal testing machine
Test specimens
Vernier Calipers
Dial Gauge

Procedure:

(A)

Familiarize yourself with the machine.  Measure and record the exact diameter of each specimen using the vernier calipers.  Mount a test specimen in the upper part of the testing machine.  Turn all of the threaded ends into the grips at both ends of the machine head.  Adjust the handwheel below the lower platter to take up all the free travel in the specimen mounting but taking care not to apply any load.  Measure the distance between the grips and record this as the original length of the specimen.  Install the dial gauge appropriately to record change in specimen length during loading.  Record the initial dial gauge reading.

- Repeat the procedure above for two other specimens of the same material.

(B)   Calculations

For the test specimens,

1.)    Draw the load-deformation diagrams for the three specimens tested on one chart.
2.)    Draw the stress-strain diagram for the three specimens tested on one chart.
3.)    Determine the yield strength, ultimate strength and rupture strength for each specimen.
4.)    Determine the average value for the yield strength, ultimate strength and rupture strength for each material.
5.)    Based on your results and material properties given in your textbook, identify the materials of the specimens, giving reasons for your answers.
6.)    The strain for this test was determined by considering the entire length of the specimen between the grips as the original length.  Would the strain be different if the smaller standard gage length of two inches had been used?  Explain.
7.)    Why is it necessary to test more than one specimen to obtain a reliable estimate of the physical properties of a material?
8.)    List the factors that influence the results obtained from this test.
9.)    What is the difference between true stress-strain diagram and nominal stress-strain diagram. Illustrate your answer using the stress-strain diagram for mild steel.
10.)    Answer true of false and state why: In tensile tests, (a) True stress is always smaller than nominal stress; (b) True strain is always smaller that nominal strain

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