Bending failure mechanisms and energy absorption design of CFRP C-frames for civil aircraft fuselage

To address the issue of insufficient bending energy absorption in Carbon Fiber Reinforced Polymer (CFRP) C-frames for civil aircraft fuselages, this study reveals the failure mechanisms and energy dissipation characteristics through quasi-static four-point bending numerical simulations and experimental benchmarking. Furthermore, the titanium alloy local reinforcement design method is proposed based on the failure mode control. The results indicate that the bending failure of the CFRP C-frame originates from the coupling effect between upper flange buckling and web bulging, which induces high interlayer stress and initial delamination at the upper corner. Consequently, the load-bearing capacity plummets to 12% of the peak load after failure, significantly constraining energy absorption. Energy dissipation exhibits significant regional heterogeneity: the web acts as the core energy absorption zone (accounting for 50.2%), followed by the upper flange (24.1%), while the upper corner, serving as the failure initiation point, contributes only 13.8%. Among the titanium alloy local reinforcement strategies, the upper corner local reinforcement (UC configuration) yields optimal performance. By leveraging the plastic deformation of titanium alloy to effectively delay initial failure, this configuration achieves a 26.1% increase in total energy absorption and a 22.3% increase in specific energy absorption, with a structural weight increase of only 3.4%. The titanium alloy local reinforcement design achieves the best balance between lightweighting and crashworthiness, providing a theoretical basis and engineering guidance for the crashworthiness design of civil aircraft fuselage structures.