Populate the \(2 \times 2\) stiffness matrix for the axial element that represents a cylindrical aluminum rod with a diameter of \(10 \mathrm{~mm}\), length of \(100 \mathrm{~mm}\), and elastic modulus of \(70 \mathrm{GPa}\). Substitute the numerical stiffness values \((\mathrm{N} / \mathrm{m})\).