A bar with a solid square cross$-$section is composed of three sections of equal length. The outer sections are made from material A and the middle section is made from

material $B,$ as shown in the figure. Assume the stress$-$strain curves for the particular materials used are as shown. What is the change in the length of the bar if a tensile load

of $104kN$ is applied? The square cross$-$section has $2cm$ sides and the length of each part is $2m.$ The elastic modulus of material $A$ is $150$GPa and the elastic modulus of

material $B$ is $100$GPa.