Two wires A and B of the same material and same length, but radius of A is twice that of B, are stretched by the same force. The ratio of elastic potential energy stored in A to that in B is:

A typical stress-strain curve: the initial straight line (Hooke's Law region, slope = Young's modulus) ends at the elastic limit; beyond the yield point, deformation becomes permanent, peaking at the ultimate tensile strength before the wire finally fractures.