Analysis of cylindrical composite shells: Examining the effects of asymmetric construction and a rounded-square cross-section

Conventional sandwich construction utilizes identical faces surrounding a lightweight core. The first part of this research examines the use of asymmetric sandwich construction for the reduction of stresses in the bending boundary layer (BBL) of a circular cylindrical shell.; A unique parameter, ø, quantifying the asymmetry of a laminate is introduced. The governing equations for a circular cylindrical shell, including the effect of asymmetric construction, are derived. A perturbation series solution in ø is found. Boundary constants for the simply supported and clamped boundary conditions are determined. The stresses for a circular cylindrical shell with asymmetry are presented. Optimization of the construction with respect to ø is conducted.; Conclusions are: (1) the shapes of the displacement and stress plots are generic, depending only on the value of ø, (2) finding a single optimum value of ø is not possible, however, ø is used to develop a figure of merit to rank materials based on their compressive and tensile strengths, and (3) core effects on stiffness calculations must not be neglected for asymmetric sandwiches.; In the second part of the research, a cylinder with a (non-circular) rounded square cross section is examined. The two-dimensional, plane-strain case including transverse shear deformation is examined. The theorem of minimum potential energy (MPE), along with power series trial functions, is used to develop an approximate solution. Comparisons to finite element analyses and other rigorous methods show excellent agreement.; A three-dimensional shell with clamped and simply supported boundary conditions is then examined. Again, MPE with power series trial functions and quadratic programming methods are used to develop an approximate solution. Comparison to detailed finite element analyses shows good agreement for short shells, but poor agreement for long shells. Finite element analyses are used to conduct a nine-parameter radius/length trade study. Extensive results are presented.; Conclusions are: (1) the power series representation and the MPE method worked well for the two-dimensional case and short three-dimensional shells, (2) the BBL response of some stresses showed unique compounding effects for short shells, (3) the BBL behavior of the three-dimensional shell was poorly predicted by conventional means, and (4) the complex response of the structure requires inclusion of higher-order effects such as transverse shear and transverse normal stress.