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Materials Testing: Tensile Tests

Extremely useful for determining various mechanical properties, the tensile test (or tension test, as it is also called) is one of the most common methods of materials testing. 

A tensile test is carried out by taking a sample of a material and subjecting it to increasing tension, stretching the sample until failure. This simple test results in the graph shown above (or something similar, depending on the material) called a stress-strain diagram. The elongation of the sample is determined with relation to the force required to produce such stretching and, knowing the cross-sectional area of the sample, the resulting stress and strain can be calculated and graphed.

This simple diagram gives a surprising number of mechanical properties, including the Modulus of Elasticity (or Young’s Modulus), yield strength, ultimate strength (also called ultimate tensile strength or tensile strength), and ductility (depending on the elongation before failure). Though less common, the stress-strain diagram can also be used to calculate the modulus of toughness and of resilience.

Along with the many properties that can be determined, another reason that tensile tests are so popular is that they can be used for almost any material. Depending on said material, the specimen is usually shaped similar to those in the bottom right image in what is called a ‘dog bone’ sample. The top left and bottom left images show brittle and ductile failure, respectively.

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Sapphire | Basil Dearden | 1959

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