experimental physics - Young's modulus and geometry of test material

When measuring Young's modulus in a material, does the geometry of the material actually matter? I have seen several references recommend that I use cylindrical pieces. But, wouldn't the tests work just as well using non-cylindrical(ex. rectangular pieces)?

Answer

Young's modulus of a material doesn't depend on geometry. It is a mechanical property of material and depend on its structure. But, we cannot determine Young's modulus of a material by its structural properties experimentally. We (in your case) want to determine $E$ (Young's modulus) by using $E=\large{\frac{PL}{A\delta}}$ in a tension test ($P$ is the tension force,$L$ is the initial length, $A$ is the cross sectional area and $\delta$ is the elongation). So, we should make our experiment conditions ideal as much as possible. For example, we should use a shape that doesn't make stress concentration as much as we can and for this aim cylindrical pieces are better than rectangular pieces.