03 May 2019 Stress-Strain Curves
Mechanical material properties are usually established by specimen tests, most commonly tensile tests, with the results shown as force vs elongation diagrams.
The results of a tensile test are hence depending on the specimen’s geometry: A bigger cross section would withstand a higher force than a smaller cross section, a longer specimen will elongate more than a shorter specimen at the same force.
To have material properties that are independent of the specimen’s geometry, the test results are converted as follows:
The force magnitude from the test is divided by the relevant (undeformed) area (for tensile tests: cross section A). The results is called Stress with the dimensions force/area (e.g. N/mm² which is the same as MPa) and abbreviated with the Greek letter Sigma σ.
The elongation ΔL from the test is divided by the relevant (undeformed) length L0. The result is called Strain and dimensionless (e.g. mm/mm) and abbreviated with the Greek letter Epsilon ε. Strain is usually a very small value and hence often shown in percent (%).
Stress-strain curves are most valuable to illustrate the mechanical performance of a material and are an important factor for a reliable FEA.
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