Abstract

During the last 20 years computational progress has significantly increased the capacity to determine the behavior of structures under complex loading conditions through finite element models analysis. This computational power can be used to build complex detailed finite element models but also to resolve more complex equations which were not possible to be coded before. Accurate buckling prediction is still a key factor on optimized structural designs. The accurate determination of the onset of buckling is absolutely essential to determine the initial point of instability and the subsequent post-buckling capability. Determining if the buckling will lead to immediate failure or the loading will be able to be redistributed afterwards is a major point to be considered. Designing a structural component with loading redistribution capability optimize the weight and increase the accuracy, so is a key objective of designers on structural components like torque boxes or fuselage skin. During years Airbus has been focused on developing accurate buckling predictions from close form solutions to complex energy methods development. This paper aims to summarize the evolution of such methods with special emphasis in energy methods and the best practices followed in Airbus for development. On top a summary of potential room for improvement and further evolution will be proposed.

Abstract

This work presents a semi-analytical approach to calculate rapidly but accurately the buckling onset of metallic and composite circular cylindrical shells with various boundary conditions under in-plane and/or pressure loads by the Rayleigh-Ritz method. Results are compared with analytical solutions and detailed finite element models reported in the literature. The proposed approach allows a quick buckling analysis of circular cylindrical shells, which makes it an ideal candidate to be used as part of an optimization scheme and/or to reduce potentially the number of detailed finite element models employed in the early design phases.

Abstract

The stability of composite material plates is being developed following basically two procedures: finite element analysis (FEA) and mathematical approaches using the energy method. The advantage of the finite element models is that they can be used with any geometry, configuration and load combination. However, it requires a significant pre-processing, computation and post-processing time of the results. On the other hand, analytical methods require much less time to obtain the results compared to them, but are limited to just basic geometries, such as rectangular panels without lightening holes. In this work, an analytical approach based on the energy method for buckling analysis of composite panels with holes has been developed. The innovation of this method is the inclusion of holes with different shapes in any position of a trapezoidal panel submitted to any in-plane loads combination. An exhaustive validation has been performed using FEA models and test results.

Abstract

The aerospace industry employs composite materials in high-responsibility structural components due to their excellent strength-to-weight ratio and suitable mechanical properties. However, their response under critical loads, such as buckling, requires advanced tools for analysis and monitoring to ensure structural integrity under all conditions. To diagnose buckling phenomena (detection, localization, characterization, and prognosis), this study proposes the use of MEMS sensor arrays and fiber optic. When properly distributed on the structure, they offer an accurate solution for such diagnosis, enabling continuous monitoring of the structural state. A system for data acquisition, visualization, and analysis will be presented to diagnose different buckling modes in a composite panel. This approach allows for structural design optimization and the development of preventive maintenance strategies for structures prone to buckling.

Abstract

The use of fiber-reinforced polymer (FRP) composites in structural applications is increasingly widespread due to their light weight and load-bearing capacity. However, their behavior under fire exposure presents unique challenges—such as thermal buckling and post-buckling response—that current regulations, including Eurocode and SOLAS, do not specifically address. This work investigates the phenomenon of thermo-inelastic buckling in composites, taking into account their flexibility, thermal degradation, and natural imperfections. A modeling approach is proposed that integrates Felippa’s corotational theory, isotropic damage models with SPROM, and thermo-mechanical coupling. These methodologies are validated across scenarios ranging from one-dimensional to three-dimensional thermal buckling, including experimental validation. The results highlight the limitations of traditional approaches based on slenderness and inelasticity, such as the Tsai-Wu method, and emphasize the need for design frameworks that incorporate structural fire response in composite materials. This work aims to bridge the gap between the growing use of these materials and the design methodologies required for fire-resistant applications.

Abstract

This study presents the compression-compression test with cruciform specimens (test CC) as a viable methodology to assess the geometric instability of a ∓45° symmetric laminate. The central region of the specimen, subjected to biaxial loading, exhibits a geometry similar to that of a square plate fixed along its entire perimeter. The bifurcation of the strains recorded at the top and bottom surfaces of the laminate is considered to be the threshold between the in-plane biaxial response and the response dominated by bending and torsional moments. The nonlinearities observed in the evolution of the stress-strain relationship in the region subjected to biaxial loading are confirmed to be independent of the response of the specimen arms. The bending-torsion coupling effects at the beginning of the bifurcation are observed experimentally in the deflection surface recorded by Digital Image Correlation. The results obtained suggest that the test CC is potentially suitable for the observation and measurement of buckling modes under various boundary conditions. However, more work is needed to reduce the quantitative dispersion. Specifically, the research should focus on minimizing geometric imperfections and load misalignments.