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Sandwich structures are widely used in lightweight construction especially in aerospace industries because of their high specific strength and stiffness. This paper investigates the effect of core thickness and intermediate layers on the mechanical properties of a polypropylene honeycomb core/composite facing multilayer sandwich structure under three points bending. We developed a theoretical model which makes it possible to calculate the shear properties in multi-cores. The results obtained by this model are agreed with our experimental results, and the results obtained with bending test showed that the mechanical properties of the composite multilayer structures increase with core thickness and intermediate layers.Keywords: Sandwich, multi-layer, bending, polypropylene honeycomb, thickness, intermediate layers Struktury warstwowe są szeroko stosowane w lekkich konstrukcjach, szczególnie w przemyśle lotniczym, z powodu ich wysokiej wytrzymałości i sztywności. Zbadano wpływ grubości rdzenia i warstw pośrednich na właściwości mechaniczne polipropylenowego kompozytu o strukturze plastra miodu (rdzeń) i wielowarstwowej struktury w trakcie trójpunktowego zginania. Opracowano model teoretyczny, który umożliwia obliczenie właściwości ścinania w przypadku wielu rdzeni. Uzyskane wyniki modelowania są zgodne z naszymi wynikami eksperymentalnymi, a wyniki uzyskane w teście zginania wykazały, że właściwości mechaniczne kompozytowych struktur warstwowych rosną ze zwiększeniem grubości rdzenia i warstw pośred-nich.

International audienceThe in-plane compressive behavior of two- and three-dimensional woven composite was investigated at high strain rates. The Split Hopkinson Pressure Bar is employed to test the high strain rate dynamic mechanical properties of E-glass vinylester composite material. For three-dimensional woven composite, two configurations were tested: compression responses along the stitched direction and orthogonal to the stitched direction. Dynamic compression properties for two- and three-dimensional are determined and compared. Experimental results show that the strain rate has a significant effect on the two- and three-dimensional woven composite response. It is observed that the three-dimensional woven composite has higher compression strength and dynamic modulus than the two-dimensional composite at high strain rate. For this study, a high-speed camera was used to determine the damage kinetics under dynamic load. The two-dimensional woven composite is mainly damaged in a mode of matrix cracks and severe delamination, while the mode for three-dimensional woven composite is mainly cracking of matrix and delamination for in-plane along to the stitched direction and shear banding failure for in-plane orthogonal to the stitched direction

International audienceWithin the EUCLID project, ‘Survivability, Durability and Performance of Naval Composite Structures’, one task is to develop improved fibre composite joints for naval ship superstructures. In many practical situations, the structures are subjected to loading at very high strain rates like slamming, impact, underwater explosions or blast effect. Material and structural response vary significantly under such loading as compared to static loading. In this paper, the results from a series of Split Hopkinson Pressure Bar tests on the woven composites are presented. These tests were done in two configurations: in-plane and out-of-plan compression test. It is observed that the failure strength varies with the different loading directions. The results indicate that the stress–strain curves, maximum engineering stresses and strains evolve as strain rate changes. The woven composites have higher values of engineering stress and dynamic stiffness for in-plane than for out-of-plane compression at the same strain rate; however, the in-plane strain at maximum stress is higher than that of out-of-plane compression. During the experiments, a high speed camera was used to determine the damage mechanisms. The specimens are mainly damaged in a crushing and shear failure mode under out-of-plane loading, as for in-plane test, the failure was dominated by fibre buckling and delamination