Imperfection sensitivity analysis for a composite bowed-out shell under axial compression

In this article, we present a systematic work to investigate the imperfection sensitivity of composite bowed-out shells with different layup patterns under axial compression. Two types of geometric imperfections, including eigenmode-shaped imperfections (produced by a first-order eigenmode imperfection approach and an N-order eigenmode imperfection approach) and dimple-shaped imperfections (produced by a single perturbation load approach and a multiple perturbation load approach), are introduced into the finite element model to predict their knock-down factors. For the eigenmode-shaped imperfections, we show that the knock-down factors predicted by the first-order eigenmode imperfection approach are riskier than the ones predicted by the N-order eigenmode imperfection approach. When adopting the single perturbation load approach, we reveal that the direction of a dimple on the shell makes a negligible effect on axial pressure bearing capacity, while the amplitude of a dimple on the shell plays a significant role in affecting the knock-down factors. Using the multiple perturbation load approach as an extension of the single perturbation load approach, we uncover that the knock-down factors predicted by the multiple perturbation load approach are more conservative than these achieved by the single perturbation load approach. In addition, we also find that the composite bowed-out shells are more sensitive to dimple-shaped imperfection than eigenmode-shaped imperfections. This work provides helpful findings for designing an airplane body and marine risers.