Question

A cylindrical pressure vessel with flat ends of length 6 ft and inner diameter of 35 in. is subjected to an internal gauge pressure of 150 psi. Neglect the end effects and the mass of ends of the pressure vessel in your design. Take the factor of safety as 1.95:

1. Design the radial thickness of the pressure vessel using steel. For steel, assume that the Young’s modulus is 30 Msi, Poisson’s ratio is 0.3, specific gravity of steel is 7.8, and the ultimate normal tensile and compressive strength is 36 ksi.

2. Find the axial elongation of the steel pressure vessel designed in part (1), assuming plane stress conditions.

3. Find whether graphite/epoxy would be a better material to use for minimizing mass if, in addition to resisting the applied pressure, the axial elongation of the pressure vessel does not exceed that of the steel pressure vessel. The vessel operates at room temperature and curing residual stresses are neglected for simplification. The following are other specifications of the design:

Only 0°, +45°, –45°, +60°, –60°, and 90° plies can be used.

The thickness of each lamina is 0.005 in.

Use specific gravities of the laminae from Example 5.6.

Use Tsai–Wu failure criterion for calculating strength ratios.

Answer 1