As you know that tensile stress-strain curves are generally used for defining the material properties. These curves are obtained with tensile tests that applied to material specimens. Also there is other material definition curves called compressiın stress-strain curves. Compression of specimens have different mechanics compared to tensile stress application to specmens. Because of this reason, compression stress-starin graphs are different from tensile stress-strain graphs.
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 compression process is plotted, the shape of this curve will be like above. The elastic region will be like tensile stress-strain curve of related material. And there wil be a yield point for compression process at the end of the elastic region. But you can see the difference compared with tensile strain-stress curves at plastic region. There is a rapid increment on stress compared to strain in compression stress-strain curve above.
There are two reasons for it;
Because of these two reasons, there is a rapid incerement on the stress value at compression stress-strain curve above.
Because of the friction that is stated above, the middle cross sections of compressed specimen tend to be much more increased. This phenomenon leads to situation that called ‘barreling’. This is the special situation for compression tests of materials like ‘necking’ in tensile stress tests.
There are lots of compression applications to materials in certain manuıfacturing processes such as rolling, forging and extrusion. These compression datas mentioned above can be used in the designing of these manufacturing processes.
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