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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.

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Evolution of the ballistic threat has taken place, principally, in the contexts of general war, terrorism and crime. The threat has been developed to cause injury or damage to personal, land vehicles, ships, aircraft and structures. Inert projectiles will cause only localized damage to structural targets and therefore normally constitute a less potent threat to the survival of the structure than rounds which have high explosive contents. This paper describes the spectrum of ballistic threats on armoured structures. The results from FEM simulations of steel projectile penetrating sandwich honeycomb armours are discussed. The simulations are performed in 3D AUTODYN software [1]. Finally, the armours with composite systems and different materials subjected to blast loads will be discussed. The results show that the ceramic-faced armours cause reduction in projectile exit velocity by about 29.4 % and 39.6% for ceramic thicknesses 10 mm and 20 mm respectively. Also the result indicate that the honeycomb reduce the displacement due to blast loads by about 77.24%, only with 3.586 % increasing in the total weight of the armours.

Due to the rapid scientific and technological developments in the aerospace industry, the requirement for safety and energy absorption efficiency is increasing, and in order to achieve that target, the analyzing of the sudden crash is required to know how to reduce it. Therefore, the main objective of the present work is to analyze the crashing response of the hybrid composite fuselage structure during different impact landing conditions. Moreover, extract the maximum acceleration at the most important locations in the UAV fuselage where most of the critical system is installed. The explicit non-linear finite element software LS-DYNA/WORKBENCH ANSYS is chosen to simulate the crushing of the referenced and the proposed UAV fuselage and investigate the maximum crushing accelerations responses on the payload under different landing conditions. The numerical results show that strengthen the fuselage structure using hybrid composite material has a notable effect on the energy absorption, and transferred acceleration on the payload. Moreover, the hybrid composite fuselage structure can reduce the transferred acceleration on the payload up to 39.65% in comparison with the metal fuselage. In addition, to study the crash analysis during sudden accidents is very important, in order to find the way to reduce it, but can’t avoid it. Hence, the UAV payload should be arranged to avoid the maximum acceleration.