High-velocity impact response on advanced hybrid composite structures

The use of composite materials of various types and forms has become a significant engineering solution for manufacturing a range of mechanical, aerospace and automotive structures, leading to a significant increase in payload, weight reduction, speed, fire resistance, manoeuvrability and durability in comparison with traditional structural materials [1, 2]. However, the investigation of their mechanical behaviour under high-velocity impact loads is particularly challenging owing to the generation of simultaneous and multiple failure phenomena with an inevitable detriment of residual in-plane properties [3]. In this paper, experimental tests and finite element methods (FEM) were performed on plates and T-stiffened laminates under transient dynamic loading, aiming at better understanding the damage tolerance, failure phenomena and impact damage of these composites. The 3D explicit model, based on continuum damage approach, was built using a DYNA3D suite on a framework of an orthotropic constitutive behaviour with stress-based and energetic failure criteria. Numerical results were validated using visual and ultrasound (C-scan) evaluation from dynamic tests. Furthermore, based on the results of the experimental campaign and the numerical model, a numerical study on the optimisation of the structure of the laminate was carried out, considering the inclusion of a secondary hybrid layer within the layup sequence. The mechanical characteristics and geometry of this secondary phase were studied in order to find the best configuration to optimise damage tolerance and improve dynamic response to out-of-plane loads. Several examples with different initial conditions were carried out on the new hybrid material to demonstrate the excellent predictive capability of the numerical model and to study the influence of new hybrid characteristics on the impact responses and impact-induced damages. Numerical results of analyse and their trend were then presented, showing a decrease of -22%, -33% and -94% in damaged area, a decrease of -33%,-57%, - 58% in maximum indentation and an increase of +62%, +134% and +156% in rebound velocity of projectile due to the presence of TPU layers with 0.25 mm, 0.5 mm and 1 mm of thickness respectively.