Design considerations for buckling of composite cylindrical shells on elastic foundations

Cylindrical shell structures are widely used in aerospace engineering, and buckling considerations often drive their design. However, cylindrical shell structures under compression loading are highly sensitive to imperfections of different nature. Indeed, geometrical, material, loading and boundary imperfections can severely reduce their load-carrying capability. 

Despite considerable research devoted to geometrical imperfections, relatively little attention has been given to the effects of boundary imperfections on the buckling load of cylindrical shell structures. However, boundary imperfections can reduce the buckling load by more than 50%. As a result, investigating both the effects of boundary imperfections and the stiffness of the cylinder's surrounding structure becomes important for more accurate predictions of their buckling loads.

Therefore, this thesis addresses the effects of boundary conditions and elastic edge support on the buckling behaviour of composite cylindrical shells under axial compression. First, the buckling behaviour of a fully homogenised quasi-isotropic cylindrical shell structure under compression is investigated under several combinations of boundary conditions. Besides these considerations, three different knockdown expressions for axial, radial and tangential elastic foundations are developed to assist designers in estimating the critical buckling load of thin cylindrical shells with elastic foundations.

In addition, the presence of bend/twist anisotropy effects in combination with boundary conditions can reduce the critical buckling load of quasi-isotropic composite cylindrical shells by 61%. As a result, a thorough investigation is conducted for laminates with low, medium and high levels of bend/twist anisotropy. Furthermore, new empirical formulae are devised for axial, radial, and tangential elastic foundations to compute the upper and lower bounds of the critical buckling load, representing various boundary conditions at the ends of the cylinder. 

Finally, potting supports around cylindrical shells are widely used to apply a uniform compression load and avoid edge crippling during laboratory testing. Therefore, the effect of potting single-sided potting and double-sided potting was investigated and found to significantly alter the buckling response of cylinder under axial compression by changing the nature of the boundary conditions.