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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.

State-of-the art studies of impact crushing circular stepped tube (inversion tube) introduce various approaches to improve the energy absorption capacities. Adding external longitudinal stiffeners on the circular stepped tubes is a new approach that have a great effect and interest. In the current study, finite element analysis using (LS-DYNA/WORKBENCH ANSYS) is performed on a series of numerical models of aluminum circular stepped tubes that are externally stiffened by a constant number of longitudinal stiffeners distributed around the cross section of the circular stepped tube. The numerical models are implemented under an axial impact crushing scenario. Furthermore, a new improved formula for prediction of steady inversion load is proposed. The theoretical predictions are found to be in good agreement with the numerical results with an error within 12%. A comparative study is conducted to compare the energy absorption characteristics and inversion mechanism between the newly proposed tubes and the conventional stepped tube. The results showed that addition of external longitudinal stiffeners on circular stepped tubes could imply greatest improvement for the energy absorption up to 104%, specific energy absorption capability (energy absorption per unit mass) up to 54.9%, the crush force efficiency up to 40.3% and increase the inversion stroke length in comparison with the unstiffened circular stepped tubes. A newfound role of external longitudinal stiffeners added to the stepped tubes that controls the inversion and deformation mechanism is presented.