Carbon and glass dry fibre bundles were inserted into a ROHACELL® 71HERO polymethacrylimide foam core under a specific inclination angle and pin pattern in order to enhance the compressive strength and stiffness of the core material. Flatwise compression tests were conducted on pin-reinforced sandwich specimens and unreinforced sandwich to investigate the effect of pin volume fraction and pin material on the compressive mechanical properties and energy absorption characteristics. X-ray computed tomography was performed on tested specimens to investigate the failure modes under compressive loads. It was concluded that the compressive strength is mainly controlled by pin failure due to bending and compression loads at pin base. Moreover, increasing the pin volume fraction improved the compressive properties of the sandwich but using glass fibre pins instead of carbon fibre pins led to a higher increase of the absorbed crushing energy. Finally, an existing analytical model to predict the compressive strength and stiffness has been tested and evaluated.

In the present paper, the influence of tailored load introduction inserts applied to a bolt-loaded open-hole injection plate with different short glass fibre content is investigated. The tailored load introduction inserts made with a Tailored Fibre Placement (TFP) process, as well as open-hole injection plates without an insert were considered as reference samples. The samples were tested under tensile bolt-loading. The influence of the TFP-inserts on the load bearing properties of the open-hole injection plates was investigated. The test results show a huge increase of the load-carrying ability of the short-glass-fibre specimens when TFP-inserts are integrated. Moreover, the damage tolerance was dramatically improved as the specimens with integrated TFP-inserts did not fail abruptly and a residual strength higher than the strength of the test specimen without insert could be observed. However, the strength of the test specimen with integrated insert did not exceed the strength of the insert itself in most cases.

The use of sandwich structures is well established in industrial sectors where high stiffness and strength combined with lightweight are required, like in marine, wind turbine and railway applications. However, the vulnerability of sandwich structures to low-velocity impacts limits its use in primary aircraft structures. Pin reinforcement of the foam core enhances the out-of-plane properties and the damage tolerance of the foam core. In this paper, a finite element model is proposed to predict the impact behaviour of pin-reinforced sandwich structure. An approach based on the building block approach was used to develop the model. Multi-scale modelling in the impact region that considers the delamination of the face sheet using cohesive zone elements was employed to increase the accuracy of the simulation. Impact tests were performed to validate the numerical model. A good agreement between numerical and experimental results in terms of contact-force displacement history and failure mode was found.

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