Experimental and theoretical study on the response of the X-frame CFRP sandwich beam under the local impulsive loading

The impact resistance of the carbon fibre reinforced X -frame sandwich beam and its foam reinforced structure was investigated experimentally and theoretically. To simulate the blast loading on the composite sandwich beams, the aluminum foam projectiles were utilised to impact the composite specimens. Under the local impulsive loads of the different intensities, the core shear failure, core crushing and skin fracture of the sandwich beams were observed by using a high-speed camera. A theoretical model for the dynamic response of the fibrereinforced composite sandwich beam under the impact loads was constructed. Three phases, namely the local compression, the propagation of global bending/shearing wave and global stretching were considered in this theory. The theoretical model can provide the reasonable deflection history and failure modes of the sandwich beam compared with the experimental and simulated results. The impact pressure between the foam projectile and the beam were obtained by the theoretical and numerical predictions. The results indicated that the decreasing of the structural density can reduce the transmitted impulse. The optimal design charts were constructed by introducing the normalised variables based on the theoretical model. The minimum weight design revealed that the composite sandwich beams with low -density cores generally had the better specific impact resistance, while the foam -filled sandwich beams with the higher density had the outperformed impact resistance at the low impulse. It is expected that the theoretical model can provide a useful reference for predicting the impact resistance of the fibre -reinforced composite sandwich structures.