Abstract The wing leading edge is one of the aircraft structures which are vulnerable to birdstrike. Therefore, Federal Aviation Regulation has clear requirements of anti-birdstrike performance for wing leading edge. However, the impact location is not specified in aviation regulation. The forefront of the wing leading edge is selected as a critical location for the birdstrike in most researches. But the rationality of the selection is not given. This paper proposes an analytical method for determining the critical location that causes the most severe damage under impact due to birdstrike. The analysis is based on the concept of effective impact, i.e. the component of the bird velocity perpendicular to the surface of wing leading edge. A birdstrike model is established using Pam-crash and used to validate the analytical prediction. The numerical model proves its effectiveness compared to the birdstrike test. The residual compressive strength of the spar when the birdstrike is at the critical impact location determined by the proposed method is 44.5% of that at the traditional impact location. Moreover, the critical penetrating velocity of the traditional impact location is not the lowest. In other words, the traditional impact location is not the weakest. Airworthiness verification experiment of birdstrike on wing structure should pay attention to this aspect.

Abstract Metal foams have been widely used in the engineering fields due to its excellent energy absorption capacity under impact. Under different impact velocities, metal foam exhibits different energy absorption properties. It is important to investigate the mechanism and behavior of energy absorption of metal foam under impact. In this study, a 3D microscopic finite element model (FEM) of metal foam is first established to study energy absorption properties of metal foam. It is shown that the impact energy transfers into kinetic and internal energy of metal foam which varies under impact. The variation can be explained by plastic shock wave, which is produced and then propagates under impact. The theoretical model is proposed to discuss and predict kinetic energy and the difference between dynamic and quasi-static energy absorption behavior of metal foam. Effects of inertia and base material strain rate on plastic shock wave are investigated, and the mechanism of the two effects on dynamic energy absorption properties are studied. The results indicate that base material strain rate effect resists the formation of plastic shock wave, and leads to smaller kinetic energy, but higher internal energy.

Abstract Increase of energy absorption along with smooth load displacement curve, reduced peak force and high mean crushing force is the key in the modern dynamic design of structures. In this regard, a new metallic tubular configuration consisting of uni-sectional bi-tubular inner tubes, with outer tubes of multiple varied cross-sections is proposed and crushed under axial dynamic loading. A number of configurations are proposed ranging from simple to complex polygonal sections defined in three groups. Deformation modes and energy absorption characteristics such as peak crushing force, mean crushing force, and specific energy absorption are determined and discussed for each configuration. The proposed arrangement shows a stable crushing and higher values of crush force efficiency. In order to select the most suitable configuration, on the basis of maximum specific energy absorption, peak crushing force and minimum peak force, a robust decision making method known as Complex Proportional Assessment (COPRAS) is implemented. The optimal configuration in each group is determined on the basis of higher values of specific energy absorption, crush force efficiency and a lower value of peak crushing force, using the chosen weighting factors in COPRAS implementation. Finally, the configuration with inner and outer hexagonal tubes is found to be the best possible design concept among the top members of each group, with peak crushing force, mean crushing force and crush force efficiency values of 69.8 KN, 7.3 KJ and 0.75, respectively.

Abstract Thin walled multi-cell columns are highly efficient energy absorbers under axial compressions. Multi-cell features are usually obtained by placing stiffeners or ribs to get the required geometry features in the columns. In this study, the curved stiffeners with varying numbers in different configurations are used to support the circular single and bi-tubular metallic tubes and their shape, position and number effects are numerically investigated under dynamic axial crushing loads. Number of configurations can be classified by the number of tube/tubes and curved stiffened shells. This study can be divided in three parts; single tubes with cross-curved stiffeners with equal number of cells, single tubes with curved stiffened wall supports with ascending number of stiffeners, and bi-tubular tubes with ascending cross-curved stiffeners. The mass in each configuration is maintained as same by adjusting the thicknesses of the stiffeners. Energy absorption for all of the configurations are compared with published experimental literature of standard single tube and single tube with cross-straight stiffeners. Deformation modes and energy absorption characteristics are evaluated and discussed for all of the proposed configurations. Results indicate that the proposed configurations with curvy stiffeners are superior in energy absorption with increased mean crushing force and enhanced energy absorption along with a high value of crush force efficiency in comparison with the refernce configurations. Bi-tubular configurations with curvy stiffeners show a more stabalized response with the lowest peak crushing force in all of the proposed configurations.

Abstract Thin walled multi-cell columns are highly efficient energy absorbers under axial compressions. Multi-cell features are usually obtained by placing stiffeners or ribs to get the required geometry features in the columns. In this study, the curved stiffeners with varying numbers in different configurations are used to support the circular single and bi-tubular metallic tubes and their shape, position and number effects are numerically investigated under dynamic axial crushing loads. Number of configurations can be classified by the number of tube/tubes and curved stiffened shells. This study can be divided in three parts; single tubes with cross-curved stiffeners with equal number of cells, single tubes with curved stiffened wall supports with ascending number of stiffeners, and bi-tubular tubes with ascending cross-curved stiffeners. The mass in each configuration is maintained as same by adjusting the thicknesses of the stiffeners. Energy absorption for all of the configurations are compared with published experimental literature of standard single tube and single tube with cross-straight stiffeners. Deformation modes and energy absorption characteristics are evaluated and discussed for all of the proposed configurations. Results indicate that the proposed configurations with curvy stiffeners are superior in energy absorption with increased mean crushing force and enhanced energy absorption along with a high value of crush force efficiency in comparison with the refernce configurations. Bi-tubular configurations with curvy stiffeners show a more stabalized response with the lowest peak crushing force in all of the proposed configurations.