S. Schindler:

"Stress concentrations in cylindrical shells with geometric imperfections under external pressure";

Talk: 10th International Conference on Pressure Vessel Technology, Vienna University of Technology; 2003-07-07 - 2003-07-10; in: "Pressure Vessel Technology 2003", Österreichische Gesellschaft für Schweißtechnik, Wien (2003), ISBN: 3-9501528-1-4; 121 - 126.

Discontinuities and departures from the intended ideal shape of cylindrical vessels, like axial misalignment, angular distortion and out-of-roundness, will cause local or global increases in pressure induced stresses in shells. These additional stresses reduce cyclic fatigue life quite often considerably. If the allowable manufacturing tolerances, given in prEN 13445 Part 4, are met, these additonal stresses are already taken account of in the fatigue design curves. If the assembly tolerances are exceeded, these additional stresses have to be considered seperately. For some shape distortions stress concentration factors are given in prEN 13445-3, but for internal pressure only, none for external pressure.

But the behavior of such imperfect vessels under external pressure is also of practical interest, i.e. for jacketed vessels. Therefore, the behavior of such imperfect shells under the action of external pressure was studied with Finite Element Analyses including nonlinear goemetry effects, and linear-elastic constitutive law.

Two deviations from the design shape were considered seperately: angular distortion and out-of-roundness. To study the influence of the length of the vessel, models with different length to diameter ratios were created. This leads to the question of the dependence of the linear-elastic buckling pressure on the way of modelling the boundary conditions at the ends of the cylinder. Different boundary conditions have been considered, e.g. locking all constraints at the end of the cylinder, or modelling different types of stiffeners.

The various results will be discussed in the presentation, and proposals for incorporation in standards given.

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