Reliability-based knockdown factors for composite cylindrical shells under axial compression

A collection of all available literature data upon experiments of composite cylinders under axial compression is performed. Theoretical estimation of bifurcation load for all the tested cylinders is achieved solving stability differential equations with the use of a combined “bi-modal and torsion” solution and Galerkin approximation. Experimental knockdown factors with respect to theoretical predictions are derived and they are used to tune the imperfection amplitude of an in-house code, which computes collapse load of imperfect cylindrical composite shells using an axy-symmetric sine-shaped imperfection. “Equivalent imperfection amplitudes” are statistically analysed and with the help of imperfections sensitivity curves, Monte Carlo simulations are performed in order to obtain new reliability-based knockdown factor for cylinders with different stacking sequences. The values obtained directly by statistical analysis of the tests results and the ones derived by the statistical analysis of the calibrated imperfection amplitudes represent an improvement with respect to old design values extrapolated from isotropic shells.