Investigations related to most critical imperfections of composite structures

Abstract

This work presents a numerical investigation about the different methodologies to characterize the behavior of imperfection sensitive structures subjected to compressive loads up to the post-buckling regime. The aim is propose a reliable numerical methodology to use as a design tool, for unstiffened composite cylinders, to calculate less conservative knock-down factors than the obtained with the classical approaches, like the NASA SP 8007 guideline. Two new approaches to take into account geometrical imperfection effects in finite element models are presented and discussed. The first methodology called “Single Perturbation Load Approach” (SPLA) was proposed by Hühne (2008) as a simple way to calculate less conservative knock-down factors than the NASA SP 8007 guideline. The second methodology, called “Multiple Perturbation Load Approach” has been developed in order to compare the reliability of the SPLA and verify the range of applicability of these methodologies among other most conventional approaches, such as geometric imperfections from the linear combination of buckling modes calculated in linear buckling analysis.