Axial Stress compression, poissons ratio ect.

steve2510

1. The problem statement, all variables and given/known data
A solid cylindrical bar 18.34 mm diameter and 180 mm long is welded to a hollow tube 18.34 mm internal diameter and 120 mm long to make a compound bar. Determine the external diameter of the tube in (mm) if when loaded with an axial force of 40 kN, the stress in the solid bar is the same as the stress in the tube.
E = 210 GN/m2, n = 0.3



2. Relevant equations
σ=F/a
ε=ΔL/L
Poisson's ratio = ε_t / ε_l

3. The attempt at a solution
I know how to find the strain in the first tube, and if they are equal then its the same in the second tube, but then I'm not sure what i can do from there, i don't no what the n=0.3, i assumed it might be poisson's ratio, so i tried to do the longitudinal stress i calculated and found out the transverse stress but i don't have a clue how i can use this..