# Compression Stress-Strain Characteristics Of Materials

As you know that tensile stress-strain curves are generally used for defining the material properties. These curves are obtained with tensile tests that are applied to material specimens. Also, there are other material definition curves called compressiın stress-strain curves. Compression of specimens has different mechanics compared to tensile stress application to specimens. Because of this reason, compression stress-strain graphs are different from tensile stress-strain graphs.

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## What Is Compression Stress-Strain Graphs In Materials Science?

Because of the formula of elasticity modulus E, in compression, the compression elasticity modulus of materials must be negative. But in the compression calculations, compression elasticity modulus values are taken as positive.

If the stress-strain curve of the compression process is plotted, the shape of this curve will be like above. The elastic region will be like the tensile stress-strain curve of related material. And there will be a yield point for the compression process at the end of the elastic region. But you can see the difference compared with tensile strain-stress curves in the plastic region. There is a rapid increment in stress compared to strain in the compression stress-strain curve above.

There are two reasons for it;

• In compression, the cross-sectional area of the specimen increases because of the compression.
• There is a friction force between the compression device and the specimen top surfaces. So the device must outcome this friction force also with compression force.

Because of these two reasons, there is a rapid increment in the stress value at the compression stress-strain curve above.

Because of the friction that is stated above, the middle cross-sections of compressed specimens tend to be much more increased. This phenomenon leads to the situation called ‘barreling’. This is the special situation for compression tests of materials like ‘necking’ in tensile stress tests.

## Conclusion

There are lots of compression applications to materials in certain manuıfacturing processes such as rolling, forging, and extrusion. These compression data mentioned above can be used in the designing of these manufacturing processes.