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Damage and failure progression of CFRP foam-core sandwich structures

: Rinker, M.; Zahlen, P.C.; Schäuble, R.

Ferreira, A.J.M. ; Univ. Porto, Faculty of Engineering:
8th International Conference on Sandwich Structures 2008. Proceedings. Vol.2 : 6 - 8 May 2008 in Porto/Portugal
Porto: Publindùstria, Produção de Comunicação, 2008
International Conference on Sandwich Structures <8, 2008, Porto>
Fraunhofer IWM ()
failure behaviour; load introduction; reinforcement element; crack propagation

This paper deals with the mechanical investigation of 3-D reinforced CFRP foamcore sandwich structures. Whereas the not reinforced sandwich carries ideally in plane loads, out of plane loads are critical. Therefore reinforcement elements like CFRP hollow profiles, CFRP double T-beam and CFRP pins in thickness direction are integrated in the sandwich and have to be benchmarked for effectiveness. For analyzing the material behaviour of the reinforced sandwich it is necessary to know the material behaviour of the not reinforced sandwich. Therefore firstly bending tests were conducted and the deformation and failure behaviour were investigated. Several failure criteria were tested by finite element calculation to describe the foam-core failure. It was possible to show, that the consideration of residual stresses increases the accuracy of failure prediction. For the investigation of the effectiveness of the reinforcement elements, special tests were defined and adapted for reinforced sandwich respectively: out of plane compression test, out of plane shear test and 4-Point-bending test. The test results have shown, that both the stiffness and strength related to weight can be increased significantly with the reinforcement elements. Cracks in the sandwich are critical because they are not visible, if they are located in the foam or in the interface foam-skin. To decrease crack propagation crack stopper can be integrated in the sandwich. The potential of the load introduction (reinforcement) elements as crack stoppers needs to be analyzed. Therefore fracture mechanic tests like ENF and DCB were defined for the investigated sandwiches with and without reinforcement elements.