Why is the uniaxial tension test commonly used to evaluate the mechanical properties of metals?

Because with this test you can determine complex material parameters like Young's modulus, yield strength, ultimate strength and elongation at break. This is important because it provides us with the factor of safety that needs to be built-in the products using these materials.

Explanation:

This test consists in place the material between to tweezers to subdued the material into a stress-strain test. The figure shows the procedure.

In the x axe the strain and the y axe the stress.