FULLY STRESSED THICKNESS PROFILE DESIGN AT DISCONTINUITIES OF AXISYMMETRICAL SHELLS

In a shell structure, the discontinuity at the intersection of two she lls causes stress concentration. This paper presents a procedure which couples the Curvature Function Method with the FAST1 structural shell analysis program to find a fully stressed thickness profile which kee ps the stress at the discontinuities at the nominal stress value. The Curvature Function Method is a zero-order method that requires only st ress values along the shell, not gradients of the stresses with respec t to the design variables, and the resulting thickness profile has C2 continuity. Although the method is independent of the structural analy sis program used to determine stress values, Fast1 provides a particul ar advantage because it allows the user to model complex shells with o nly a few large shell elements and still retain a sufficiently accurat e solution. Thus both preparation and computation times are reduced su bstantially. Convergence of different initial designs to one final des ign using this procedure is demonstrated for a cylinder-cone intersect ion problem. This procedure is also applied to two other shell models with multiple discontinuities to find their fully stressed thickness p rofiles. The procedure presented in this paper provides a practical te chnique and tool to aid the design engineer, although the fully stress ed design may not be the theoretically optimal design of minimum weigh t.