Manufacturing, testing and modelling of hybrid aluminium foam - CFRP sandwiches with improved impact strength

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The usage of sandwich materials in structural applications in the automotive and railway traffic is in constant need of surveying the crash and impact security to ensure the safety of passengers and vehicle structural integrity. The wide spread paper-core based sandwich composites often lack the high compression and impact strength needed for structural applications. Hybrid sandwich composites of shear-resistant metallic foam cores and carbon fiber reinforced face sheets provide an enormous potential of energy absorption. Additionally the aspect of hybrid lightweight design is enhanced through multilayer build up with high tenacity face sheets. Therefore in this proposal the important aspects of CFRP-Al-foam sandwiches are focused and illustrated. First of all the optimization of the face sheet deposition is performed for the innovative PU spraying process which is suitable for series production. Therein different material combinations and influence factors on the process stability are investigated for lightweight design. These are then characterized using static and dynamic material testing to provide detailed mechanical properties of elastic and plastic deformation in the core, face sheet and their interface. Using these variables basic conclusions about the mechanical behavior during real life application and loading can be made and the relations between process, structure and mechanical properties can be identified. The structural characterization will be further developed according to the central role for the multi material system. Especially tomographic measurement methods will be applied and enhanced to hybrid sandwich composites due to their advantages of 3D image analysis for damage evolution characterization and micro- and meso-structural analysis. The experimental data studied in material testing and structure characterization finally builds the fundamental insight supporting a micro-mechanic modelling of the sandwich composite and design details for structural integrity and composite parts. The models used so far for conventional sandwich structures have to be adjusted to the material combination based on the structural findings and the measured component properties which will then be compared to the mechanical behavior of the sandwich structure and validated with the experimental data from sandwich testing. The final objective is a comprehensive understanding of the material combination and the effects based on the interface and mutual interaction providing guidelines and data for the dimensioning of sandwich parts in the afore mentioned application area.