Design of a crash energy absorber for a composite aircraft fuselage using a combined analytical-numerical approach

Abstract

This thesis aims to provide more insight into the crashworthiness behaviour of a composite aircraft fuselage. This is achieved by studying both analytically and numerically the crushing behaviour of composite energy absorbers. The analytical model, which is based on energy dissipation rates, generalises previously derived analytical models to study a wider variety of structural components. It is found that the analytical model can give an estimation of the mean crushing load of square, C-shaped, and corrugated specimens. Next to the analytical study, numerical models are created to gain insight into the behaviour of the studied shapes when subjected to crash loading. Another part of the numerical study investigates the effectiveness of different material models to capture the complex failure mechanism of the composite crash absorber. In LS-Dyna, the MAT054, MAT058, and MAR262 material models are used, which are all able to reproduce the results obtained from reference tests. The ability of the material models to recreate the crushing phenomenon is thought to originate from the opportunity LS-Dyna offers to degrade material properties in the crush frond, which incorporates the formation of cracks and delaminations. In the final stage of this research, a case study is performed, where different absorbers are introduced into a simplified digital twin of the Next Generation Multifunctional Fuselage Demonstration as developed by the STUNNING project. Here, it is found that the fuselage's energy absorption can be increased by introducing energy absorbers. All the simulated fuselage sections show similar behaviour in the first crash stages, characterised by the flattening of the lower section of the frame. Subsequently, the behaviour of the absorber and the surrounding structure highly depends on the absorber's integration. Finally, it is found that by combining the numerical results of a baseline fuselage section and the analytical model for the energy absorbers, one can estimate the energy absorption of the augmented structure with a discrepancy of less than 20$\%$. This proves that the suggested analytical-numerical method can aid engineers during the preliminary design for crashworthiness of a thermoplastic composite aircraft fuselage.