Abstract

Sandwich structures made of composite materials, namely glass fibre/polyester, are widely used in  the naval, ground transportation, aerospace and telecommunication industries. Due to the combination of key factors: the good mechanical properties of this kind of materials together with their low specific weight and their permeability to electromagnetic waves. These structures are often subjected to impulsive loads during its service life. Therefore, in order to obtain a safer structural design, a better knowledge of the impact response must be accomplished. It has been demonstrated that the composition of the skins plays a fundamental role in the behaviour of sandwich structures against high-energy ballistic impacts. The structures studied in this work are composed by two E-glass fibre/polyester skins and a PVC core. With the objective of optimising this kind of structures when they are subjected to high-energy impact, a numerical study in the finite element code Abaqus has been carried out. In this study, the number of plies in the front and rear faces varies in order to find the configuration that presents better ballistic performance. To this aim, a VUMAT subroutine previously developed has been used for the skins. The core has been modeled with the crushable foam constitutive model available in the software Abaqus. The influence of the thickness of the skins can be tested by means of this numerical model. The results obtained show that the residual velocity disminishes the more the number of layers in the rear skin increases.

Abstract

One of the main challenges for UAVs (Unmanned Aerial Vehicles) used in defence and military operations is to effectively conclude a flight mission in a harsh environment. The platform survivability is critical, therefore it is imperative that the vehicle is able to withstand ballistic impacts in flight and still be able to reach its destination. In the present work, the authors discuss the development of a lightweight ballistic armour to protect critical areas of the vehicle, such as the control systems and/or the payload. The structure response during and after a 9 mm bullet impact, shows that the proposed hybrid composite panels will be able to withstand high-energy ballistic impacts after optimization. The FEA (Finite Element Analysis) method is implemented to study the performance of ceramic protective plates attached to the CFRP (Carbon Fibre Reinforced Polymer) structural platform. An Eurelian-Lagrangian modelling technique is implemented with different damage models for the various materials involved in the impact event in order to properly capture each material response in this complex load scenario. Numerical studies are validated experimentally. The base structural CFRP is cured in autoclave followed by a post-cure to integrate the remaining components. Experimental tests were conducted at a shooting range where 9 mm projectiles are fired at a distance of 10 m of the target plates. Data is collected recurring to a chronograph/high speed camera combination apparatus to measure the impact and residual velocity and the projectile deformation/damage. Numerical models show good correlation with the experimentally measured data.