 Welcome back MechanicalEI, did you know that cylindrical shells were what made the piping industry possible and the Sputnik 1 had a spherical shell to shield it from the atmospheric heat? This makes us wonder, what are cylindrical and spherical shells? Before we jump in, check out the previous part of this series to learn about what deflection of a beam is. Now thin cylinders are found in the form of pipes, storage tanks, water tanks etc. In cylindrical stresses, the three principal types of stresses in the shell are circumferential or hoop stress, the longitudinal stress and the radial stress. If the cylinder walls are thin and the ratio of the thickness to the internal diameter is less than about 1 by 20, then it can be assumed that the hoop and longitudinal stress are constant across the thickness. It may also be assumed that the radial stress is small and can be neglected. For a cylinder with internal diameter D and a wall of thickness T, if the applied pressure is P, then the hoop stress is given by F1 equals P times D upon 2T and the longitudinal stress F2 is given by P times T upon 4T. Thin spheres on the other hand are found in old diving equipment and boos. As in the previous section, the radial stress will be neglected and the circumferential or hoop stress is assumed to be constant. By symmetry, the two principal stresses are equal and the stress in any tangential direction is equal to F, which is given by P times D upon 4T. A cylindrical shell with hemispherical and shaped containers are used to transport oil among other major applications. Consider a cylindrical shell with hemispherical ends having thickness T1 and T2 of the cylindrical and hemispherical walls respectively. Assuming hoop strain in both the spherical and cylindrical walls to be equal, the maximum stress will occur in the hemispherical ends and is given by considering the hemispherical ends alone, which comes out to be F equals Pd upon 4T2. Hence, we first saw how thin cylinders and spheres behave due to internal pressure and then went on to see how cylindrical shells with hemispherical ends act under internal pressure.