How to Calculate Strain to Fracture for a Tensile Test

A tensile test measures the strength of materials. The test helps manufacturers understand how much force a material can be put under before the material bends, strains or breaks. One measure of a material in a tensile test is strain, which is the change in length of the material after it has been stretched using a specified force. A strain test carried out until the material breaks is called a strain to fracture test.

Metals are often tested for their tensile strength.

Step 1

Measure the starting length of your material.  Clamp the material into the universal testing machine. Attach the extensometer according to the operating procedures for your machine. 

Step 2

Enter the load range for your material.  This varies depending on what you are testing. Start with a conservatively low load number if you're working with a new material. 

Step 3

Start the tensile test.  Go slowly and take note of the load applied by the machine and the length of the material. Use the calipers to measure the material rather than trying to fit the ruler into the machine.  Some testing machines record all information on the computer for you; for other machines you will need to take measurements manually.

Step 4

Stop the test as soon as the material breaks.  This is the strain-to-fracture point.

Step 5

Remove the material from the machine.  Fit the material end-to-end and measure its final length. This is the maximum point of elongation.  The change in the material's length is the strain. The amount of load applied is how much stress the material can handle before fracture. 

Things You Will Need

  • Ruler
  • Universal testing machine
  • Material to be tested
  • Calipers

About the Author

Based in Portland, Ore., Tammie Painter has been writing garden, fitness, science and travel articles since 2008. Her articles have appeared in magazines such as "Herb Companion" and "Northwest Travel" and she is the author of six books. Painter earned her Bachelor of Science in biology from Portland State University.

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