Comparison of new Design Guidelines for Composite Cylindrical Shells prone to Buckling

Abstract

Currently, imperfection sensitive shell structures prone to buckling are designed according to the NASA SP-8007 guideline, from 1968, using its conservative lower-bound curve. In this guideline the structural behavior of composite materials is not appropriately considered, since the imperfection sensitivity and the buckling Ioad of shells made of such materials depend on the lay-up design. Due to the fact that this approach is outdated for preliminary design purposes, several authors are investigating less conservative methodologies. Some authors propose a new lower-bound curve approach based only on statistical analysis of experimental lest on composite cylinders. The problem with this approach is that the range of applicability is limited to the database extension. Finite element models are also used by many researchers to characteristic the behavior of cylindrical shell considering different types of material and geometrical imperfections. A representative finite element model allows studying a widespread area of possibilities from the design point of view. In this context a numerical investigation about the different methodologies to characterize the behavior of imperfection sensitive composite structures subjected to compressive loads up to buckling is presented in this paper. A comparative study is addressed between new deterministic methodologies, such as the "Single Perturbation Load Approach" proposed by the European project DESICOS and new statistical approaches based on experimental test on composite cylinders. The aim of this work is to define the range of applicability of these methodologies for unstiffened composite cylinders, advantage and disadvantage to use as a design tool, to provide means to calculate less conservative knock-down factors than the obtained with the NASA SP-8007 guideline.