A composite bar has two sections of a cross-sectional area of 100mm² and 200mm² respectively. The length of both sections is 100mm. What will be the total elongation of the bar if it is subjected to the axial force of 100kN and E = 105 N/mm²?

In a bar of different sections, the resultant strain is the algebraic sum of the individual stresses.

Elongation in section 1 = 100,000 x 100 / 100000 x100 = 1
Elongation in section 2 = 100,000 x 100 / 100000x 200 = 0.5
Total elongation = 1 + 0.5 = 1.5mm.