8. (25 pts) Determine the stress in each section of the bar shown in the figure below when subjected to an axial tensile load of 20 kN. The central section is 30 mm square cross-section; the other portions are of circular section, their diameters being indicated. What will be the total extension of the bar? For the bar material E=210 GN/m² (the deformation is assumed to be elastic). 250 + 100 20 kN 20 30 400 15 Not to scale all dimensions mm 20 kN