A polyethylene bar having diameter d1 = 4.0 in. is placed inside a steel tube having inner

Question:

A polyethylene bar having diameter d1 = 4.0 in. is placed inside a steel tube having inner diameter d2 = 4.01 in. (see figure). The polyethylene bar is then compressed by an axial force P.
At what value of the force P will the space between the nylon bar and the steel tube be closed? (For nylon, assume E = 400 ksi and v = 0.4.)