Probabilistic Assessment of a Stiffened Carbon Fibre Composite Panel Operating in its Postbuckled Region

This paper presents a probabilistic study on the behaviour and buckling capacity of a thin shell carbon fibre stiffened panel operating in its postbuckling region. The paper is a part of the ongoing world wide research into this phenomena being conducted by the CRC-ACS and many other interested parties including the EU FP6 Project COCOMAT. The aim of the research is to develop proven design methods that will allow an increased specific strength of stiffened composite structures commonly used in the civil aviation industry. Unlike their metal counterparts which can be reliably designed to operate with postbuckled loads, the use of similar composite parts for primary structures has not yet been widely adopted by industry. This is mainly due to the relatively brittle nature of composites which prevents significant yield based load paths being developed local to the stiffened regions of the structure. Using LS-OPT and LS-DYNA the study explores the probabilistic variations of a COCOMAT panel using a stochastic analysis. The response of the panel was the peak buckling load and the design variables included uncertainties in material properties, manufacturing tolerances and geometric imperfections. It was concluded that three of the four ply angles require accurate orientation during placement to produce a panel that will exhibit good repeatability for experimental testing. In addition the available computational methods in LS-DYNA to simulate buckling are reviewed and compared through the testing of a small baseline model.