A composite rod is made of two equal-length segments, one of Youngs modulus Y1 and area A, and the other of Youngs modulus Y2 and the same area A, joined end to end and stretched by force F. The effective Youngs modulus of the composite rod 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.