Dynamic axial crushing behaviors of circular composite tubes with different reinforcing fibers and triggers

The choice for a proper external trigger and fiber hybridization configuration has a significant impact on the stability of the crushing process and material cost for composite structures in crashworthiness. However, there is still a lack of a thorough understanding of impact characteristics and energy-absorption mechanisms. This study explores the axial crushing responses and crashworthiness characteristics of energy-absorption composite structures by both experiment and finite element analysis. A series of dynamic crushing tests were conducted for three types of composite tubes under the same crushing velocity of 1.944 m/s, including carbon fiber reinforced polymers (CFRP), glass fiber reinforced polymers (GFRP), and CFRP/GFRP inter-layer hybridized composites. The configuration of the composite tubes includes: (i) CFRP composite tubes with a single 45° chamfer trigger (T1), a combined 45 °chamfer and outward-folding crush-cap (T2), and a combined 45 °chamfer and outward-folding crush-cap with a cavity (T3); (ii) GFRP and CFRP/GFRP hybrid composite tube with T2 trigger. A stacked-shell model was developed to investigate the energy-absorption mechanisms. Three distinct failure modes have been found for composite tubes with T1, T2, and T3 triggers, separately, named splaying, outward-folding, and outward-folding with local buckling. The CFRP composite tubes with the T1 trigger exhibited the best crashworthiness performance, while the T2 trigger reduced the friction interaction between the splaying fronds and the platen, causing a 67% reduction of specific energy absorption (SEA)/mean crushing force (MCF). In the meantime, the T3 trigger boosted 101.9% of SEA/MCF from T2. With the same T2 trigger, the GFRP composite tube showed a better crashworthiness performance than the CFRP composite tube: 35.5% reduction of initial peak crushing force (IPCF), 68.6% and 98.5% increment of MCF and SEA respectively. It has been found that the outermost layers dominated the energy absorption behavior, which matches well with the observation that replacing the central CFRP plies with GFRP ones results in similar crashworthiness characteristics between CFRP and CFRP/GFRP hybrid composite tubes. The findings in this study contribute to providing practical guidelines for the crashworthiness design of heavy duty composite structures, such as railway vehicles