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Tensile Test
Practical Course Materials Science

Procedure

Following steps are necessary:

You may use the items as chapter navigation.

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Result of Measurement

Result of measurement

Based on the force and elongation data acquired during the tensile test, engineering stress-strain-curves along with the technological relevant material parameters as well as true stress-true strain-curves, also adressed as flow curve (pages Evaluation), should be calculated.

Curve charts

Evaluation

After plotting the recorded force-elongation-curves it is now possible to select appropiate supporting points for the calculation of the engineering stress-strain-curves.

Measuring artifacts

  • During the test unwanted effects may occur and affect the measured data, for instance slip of the sample due to incorrect clamping or the area fracture is outlying the measuring markers.
  • The method used for elongation determination can have a significant effect on the resulting material parameter. If the traverse is taken into account for the strain measurement plastic deformation in the radii of the samples heads can lead to deviations compared to the extensometer signal.
  • Especially diagrams calculated by derivating, the raw data can have significant effect on the result. For instance phenomena occuring on a local scale, as observed in certain types of TWIP steels, can lead to a unsteady slope of the resulting curve. But also very high data acquisition rates of the testing maschine can cause such effect. In this case it may be necessary to smoothen the raw data before derivating it to distinguish between local phenomena or measuring effects.

Practice

Checklist The steps

1. Deburring the sample

Use the prepared abrasive paper:

To prevent measurement errors and injuries you should debur the sample thoroughly.
Additionally you avoid damaging the rubber bands holding the steel pins in place.

Caution Make sure you do not grind the edges round!

2. Measuring the sample

Use the caliper:

Caution Before measuring the caliper has to be calibrated!

Sample with round cross section:
Initial diameter (do), initial gauge length (Lo), test length (Lc), total length (Lt)
Sample with rectangular cross section:
Initial width (b), initial thickness (a), initial gauge length (Lo), test length (Lc), total length (Lt)

Take multiple measurements and average them.

3. Marking the gauge length

You need the pattern, steel pins and the rubber bands

A) First draw the dot matrix with the pattern.

B) Mark the gauge length with the steel pins and the rubber band.

C) Control the required gauge length (80 mm)

4. Preparing the measuring programm

Type the data in the program:

A) Type in the measured and averaged sample dimensions

B) Initial/start load = 0

5. Mounting the sample in the tensile test machine

Mount the sample thoroughly:

A) Define the sample position with adjusting screws.

B) Press the sample straight in the tensile test machine.

C) Clamp the sample hydraulic or by tightening the screws.

D) Control the sample position in the visual measuring field (left monitor).

E) Adjust if necessary.

6. Performing the tensile test

Checking and starting:

A) Setting the strain rate (~ 0.002 s -1) ?

B) Start the test (Button "Start")

7. Finishing the tensile test

Finishing the test:

A) Untighten the hydraulic cylinders or srews and remove the 2 halves.

B) Tape the halves together and label them.