Calculate the maximum membrane stress in the wall of shells having the following shapes. The vessel walls are 2 mm thick and subject to an internal pressure of 5 bar.

1. An infinitely long cylinder, inside diameter 2 m; 

2. A sphere, inside diameter 2 m; 

3. An ellipsoid, major axis 2 m, minor axis 1.6 m; 

4. A torus, mean diameter 2 m, diameter of cylinder 0.3 m.