Abstract

Abstract

Composites trend to failure in their defects, which are randomly distribuited. This causes that the tensile strength decreases when the volumen of material tested increases. This fenomenon is known as size effect or volume effect. Knowing the value of the Weibull parameters is key for modeling and the correct design of large components. In this work, one tensile test are proposed, named the fragmentation test to obtain the shape and scale Weibull parameters that are validated with the scaled test. Carbon/glass hybrid composites can exhibit pseudo-ductile response in the stress-strain curves by having a part with small slope or plateau. The specimen design promotes fragmentation or gradual fracture of carbon layer and suppresses unstable delamination at the plateau. The facture events have been identified by video and accoustic emission monitoring in 11 specimens. The data of fracture strain has been adjusted to the Weibull distribution following the proposed iterative process. The process has been validated using previous results of Finite Elements. The volumen effect has been validated with the results of series of tensile tests, with dimensions scaled by factors of 2,4 and 8 in each direction. Another important advantage of hybridization is the suppression of the stress concentration in the carbon layer, which makes simple end-tab free specimens feasible. The results of two tests have been compared, obtaining very close values.

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.