Cylinder compression test

Sample between the compression tracks

Specimen shape with machined lubrication pockets

The cylinder compression test is used as a material testing method to determine material properties . The cylinder compression test is a variant of the compression test with a cylindrical sample shape. The primary result of the experiment is the flow curve , from which further parameters can be derived. They include parameters of Solidification models.

In the experiment, a cylindrical sample with radius r ₀ and height h _{0 is} compressed between two parallel tool surfaces protruding beyond the sample end faces . The required pressing force F and the associated sample height h are determined. By applying Newton's third axiom , the equilibrium of forces between the force generated by the testing machine and the force exerted by the material of the same magnitude can be formulated: ${\displaystyle A}$ ${\displaystyle k_{f}\,A}$

${\displaystyle F=k_{f}\,A}$

and solve for the yield stress k _f :

${\displaystyle \Leftrightarrow k_{f}={\frac {F}{A}}.}$

Due to the constant volume

${\displaystyle A_{0}\,h_{0}=A\,h\Leftrightarrow A=A_{0}\,{\frac {h_{0}}{h}}}$

follows from this

${\displaystyle \Rightarrow k_{f}={\frac {F}{A_{0}}}{\frac {h}{h_{0}}}={\frac {F}{\pi r_{0}^{2}}}{\frac {h}{h_{0}}}.}$

The yield stress determined in this way becomes the comparison degree of deformation in the flow curve

${\displaystyle \varphi =ln{\frac {h}{h_{0}}}}$

assigned.

A uniaxial stress state is required for the equation to be valid . This requirement is no longer met if the specimen bulges with increasing deformation . The unwanted bulging can be reduced by appropriate lubrication between the tool and the specimen.

Usable ratios of sample height and diameter are between 1.5 and 2. Further information on the test parameters can be found in DIN 50106.

Further variants of the compression test are the flat compression test and the Rastegaev cylinder compression test.

literature

Dahl, W .; Kopp, R .; Pawelski, O .: Forming technology: Plastomechanics and materials science . Stahleisen, 1993, ISBN 978-3-514-00402-3 .