Stress-Strain Diagrams

Explanations

In this animation, we will show how stress can be related to strain by using experimental methods to determine the stress-strain diagram for a specific material

The strength of a material depends on its ability to sustain a load without undue deformation or a failure. The tension or Compression test is primarily used to determine the relationship between the average normal stress and average normal strain.

1.The stress-strain diagram

From the data of a tension test, it is possible to compute various values of the stress and corresponding strain in the specimen and then plot the result. The resulting curve is called the stress-strain diagram.

Stress s = applied Load P divided by the specimen’s original cross-sectional Area A₀

Strain e = the change in the specimen’s gauge length d divided by the specimen’s original gauge Length L₀.

2.Elastic behavior

If the specimen returns to its original length when the load acting on it is removed, it is said to response elastically.

3. Yielding

A slight increase in stress above the elastic limit will result in permanent deformation. This behavior is called yielding for ductile materials.

The stress that causes yielding is called yield stress s_y_.

The deformation that occurs is called plastic deformation.

4.Strain Harding.

When yielding has ended, a further load can be applied to the specimen, resulting a cure that rises continuously but becomes flatter until it reaches a maximum stress referred to as ultimate stress, s_u.

The rise in the curve is called Strain Harding.

5. Necking.

After the ultimate stress, the cross-sectional area begins to decrease in a localized region of the specimen, instead of over its entire length. So, a “neck” is formed as the specimen elongated further.

6. Experimental data was obtained from ESM lab.

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This material is based upon work supported by the National Science Foundation under Grant No. 0633602. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

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