An Analysis Tool for Design and Certification of Postbuckling Composite Aerospace Structures

Abstract

In aerospace, carbon fibre-reinforced polymer (CFRP) materials and postbuckling skin-stiffened structures are key technologies that have been used to improve structural efficiency. However, the application of composite postbuckling structures in aircraft has been limited as today's analysis tools cannot accurately predict structural collapse in compression. In this work, a finite element analysis tool for design and certification of aerospace structures is presented, which predicts collapse by taking the critical damage mechanisms into account. The tool incorporates a global-local analysis technique for predicting interlaminar damage initiation, and degradation models to capture the growth of a pre-existing interlaminar damage region, such as a delamination or skin-stiffener debond, and in-plane ply damage mechanisms such as fibre fracture and matrix cracking. The analysis tool has been applied to single-and multi-stiffener fuselage-representative composite panels, in both intact and pre-damaged configurations. This has been performed in a design context, in which panel configurations are selected based on their suitability for experimental testing, and in an analysis context for comparison with experimental results as representative of aircraft certification studies. For all cases, the tool was capable of accurately capturing the key damage mechanisms contributing to final structural collapse, and suitable for the design of next-generation composite aerospace structures. Analysis ToolThe finite element (FE) analysis tool developed was focused on predicting the collapse of stiffened composite structures in compression by capturing the effects of the critical damage mechanisms. The approach contains several aspects: predicting initiation of interlaminar damage in intact structures; capturing in-plane degradation; and, capturing the propagation of a pre-existing interlaminar damage region. The analysis tool was implemented into MSC.Marc v2005r3 (Marc) by a combination of user subroutines, and supported by utilities for pre-and post-processing within a user-friendly menu system developed in MSC.Patran. 1 This work was conducted as part of the European Commission Project COCOMAT, which focused on exploiting the large strength reserves of composite aerospace structures through a more accurate prediction of collapse. 2The approach for predicting the initiation of interlaminar damage in the skin-stiffener interface was based on a globallocal technique. In this technique, a global shell model of the full structure was used to determine the deformation field of the entire structure, which was then input as boundary conditions on a local three-dimensional (3D) brick model of a skin-stiffener interface. In the local model the strength-based "degenerated Tsai" criterion was monitored at all elements in order to predict the initiation of delamination or skin-stiffener separation. Failure was deemed to occur when the average of all integration point values in an element satisfied this criterion. By modifying the locat...

A Finite Element Methodology for Analysing Degradation and Collapse in Postbuckling Composite Aerospace Structures

“…An analysis methodology was developed to predict the collapse of stiffened composite structures in compression that is focused on capturing the effects of the critical damage mechanisms. The approach contains several aspects: predicting the initiation of interlaminar damage in intact structures; capturing in-plane degradation such as fibre fracture and matrix cracking; capturing the propagation of a pre-existing interlaminar damage region [7][8].…”

Perturbation-based imperfection analysis for composite cylindrical shells buckling in compression

“…More detailed design studies or analysis in comparison with experimental results should consider material failure, and ideally capture the progression of all critical damage modes. This has previously been demonstrated by the authors [11,12], where accurate predictions and detailed design studies of composite postbuckling panels were achieved using a progressive damage analysis methodology.…”

“…Alternatively, the use of a database of known imperfection patterns has been proposed as a means of assessing the sensitivity of a design using numerical analysis [7]. Other approaches involve taking into account non-traditional imperfections such as those involving the loading or material [8], the use of statistics-based techniques [9,10], or progressive damage modelling [11,12]. However, for these approaches, the appropriate parameters to apply are often not known a priori for a given structure and manufacturing process, so that experimental testing would be required for validation.…”

Buckling analysis of sandwich orthotropic cylindrical shells by considering the geometrical imperfection in face sheets

“…This led to the establishment of some reliable and modified guidelines based on the experimental results [8,24]. Nowadays, the non-destructive methods have attracted great interest among researchers to evaluate the actual buckling behaviors of cylindrical shells considering various geometrical imperfections [9,16,26]. Based on the reported literatures, it is concluded that the various approaches and guidelines which have been developed to predict realistic buckling loads have a lot of limitations in the shape of structure and their accuracy are dependent on the type and amplitude of imperfection.…”