The cross-sectional area of the shaft can be computed as:
A=π4[D2-d2]
=π4[(114mm)2-(102mm)2]
=2,036mm2
The axial normal stress is therefore:
σaxial=PA
=(40 kN)(1000 N/kN)2,036 mm2
=19.65 N/mm2 = 19.65 MPa