Comparative analysis of the bending crashworthiness of CFRP, metal and CFRP/metal hybrid C-frames

Abstract

Aircraft fuselage frames are the critical energy-absorbing structures, with bending failure being the primary and the most complex failure mode during crash events. A finite element model was validated through a four-point bending test of a carbon fiber reinforced plastic (CFRP) C-frame. A comprehensive comparative analysis was conducted on the bending failure behavior and energy absorption performance of C-frames made from CFRPs, metals (aluminum alloy (Al) and titanium alloy (Ti)), and their hybrid configurations (CFRP/Al and CFRP/Ti). The results showed that, under four-point bending load, all C-frames exhibited consistent local buckling in the midsection of the compressed upper flange, with failure initiating at the upper flange-web junction due to the material’s compressive failure strain. The CFRP C-frames exhibited limited energy absorption performance due to brittle fracture. Whereas the Al and Ti C-frames exhibited superior energy absorption performance via mechanisms such as local buckling, plastic deformation and ductile fracture. The CFRP/metal hybrid C-frames effectively combined the advantages of metals and CFRPs, significantly enhancing residual structural integrity and energy absorption performance through metal-induced plastic deformation and controlled CFRP failure. Compared with the CFRP C-frames, the CFRP/metal hybrid C-frames exhibited 62.9 % to 238.4 % improvement in energy absorption, 16.4 % to 73.6 % improvement in specific energy absorption, and 62.8 % to 238.1 % improvement in mean bending force. Notably, the designs with metal layer positioned outside optimally leveraged the metal’s properties, outperforming configurations with the metal layer positioned inside. These findings provide critical insights into the bending crashworthiness design of fuselage frames.