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Lightweight fibre-reinforced polymer composites are currently being applied extensively in the design of transport structures to replace conventional metallic solutions, and also in structures that are exposed to the risk of foreign object impact. Therefore, an experimental study was undertaken to assess and compare the low- and high-velocity impact behaviour of S-2 glass®, HTA carbon and ultra-high-molecular-weight polyethylene (Dyneema®) composites. Three different impact test methods were applied: Charpy pendulum impact tests, drop-weight impact tests and ballistic impact tests with a gas gun. The results with the focus on penetration energy are compared in terms of correlation between the three test methods and in terms of weight-specific material performance. While the S-2 glass® fibre showed the best performance of the epoxy-based composites, the PUR-based Dyneema® HB26 panels proved the best penetration resistance in this study.

This study assesses the bird strike resistance of the satellite communication (SatCom) radome of a medium altitude, long endurance (MALE) remotely piloted aircraft system (RPAS), which is designed as a lightweight sandwich structure with thin quartz fibre composite skins and a cellular honeycomb core. In order to perform accurate, predictive numerical bird strike simulations, the building block approach was applied, involving extensive experimental characterisation and model validation of the materials and structures from simple coupon level up to full-scale radome level. Coupon tests of the quartz fibre composite skin material under high-rate dynamic loading revealed significant strain rate effects, which needed to be taken into account in the simulation model in order to predict the structural response under high-velocity bird strike loading. In summary, this work presents a systematic and detailed approach for obtaining validated modelling methods for high-velocity impact analyses, which could be used efficiently for various design and parameter studies during the development of the SatCom radome.

The work presented in this article is directed towards the application of CFRP foam core sandwich structures as primary structures in commercial aviation. With closed cell rigid foams, it is possible to produce comparatively low priced high-integral sandwich components having a complex geometry in terms of a curved and a variable lateral cut. Sandwich structures are offering a good bending stiffness and strength to weight ratio. Thus, they are suited for using in structures which are at risk to fail by buckling (Herrmann et al. Sandwich structures 7: advancing with sandwich structures and materials, 2005). The investigations are focused on a CFRP sandwich structure with polymethacrylimide (PMI) foam core, named ROHACELL Ò RIST. Besides good structural stability at thermal conditions, the foam is characterized by a good strength and stiffness to weight ratio (Seibert, Reinforced Plast 50(1): [44][45][46][47][48] 2006). Primary structures in aircraft applications are exposed to a superposition of in-service loads and environmental conditions. The typical working loads in combination with environmental conditions were investigated. The structure needs a sizing with respect to large temperature changes and influences of humidity. Thus, the time, temperature, and moisture dependency of the mechanical behavior were studied for the single components of the structure and for the composite itself. Therefore, Finite Element Models on macroscopic level were built with reference to the experiments. For each in-service case, the residual stresses arising during manufacturing have to be regarded and quantified (John et al. ECCM14, 2010). During manufacturing, the sandwich structure is cured at 180°C. Due to the different stiffnesses and coefficients of thermal expansion of the foam and the CFRP face sheets, residual stresses are induced by cooling down to service temperature. Among others, some tests were made at laterally closed CFRP sandwich structures with a storage time up to half a year at certain climate conditions. The aging process is not only controlled by external conditions, but also by a rearrangement of molecules, for example, the relaxation behavior of the PMI foam (Gutwinski et al. Verbundwerkstoffe. Wiley, Weinheim, 2009). Another question of the long-term behavior of the CFRP foam core sandwich structure is the characteristic of delamination of the face sheets from the inner core after an impact has occurred. To describe the crack growth behavior of the sandwich structure fracture mechanical principles can be used estimating the damage tolerance. Sandwich specimens with initial damage were loaded up to 3 million mechanical load cycles.