Effect of triggering and polyurethane foam-filler on axial crushing of natural flax/epoxy composite tubes

• All flax/epoxy tubes crushed in a brittle manner with a progressive crushing pattern.
• Foam-filled tubes have better crashworthiness than empty tubes in all aspects.
• Trigger minimises force variation of tubes from average crush force.
• Trigger has insignificant effect on total energy and specific absorbed energy.
• Flax/epoxy composite tube has the potential to be used as energy absorber.

In this study, empty and polyurethane-foam filled flax fabric reinforced epoxy composite tubes were longitudinally crushed under quasi-static compression. The effects of foam-filler (density of 160 kg/m3, two diameters of 64 and 86 mm), tube thickness (2, 4 and 6 plies of laminate), and triggering (45° edge chamfering) and the combination of triggering and foam-filler on the crushing characteristics and energy absorption capacity of these tubes were investigated. The test results indicate that the observed primary failure mode was progressive crushing for all the specimens. Foam-filled tubes have better crashworthiness than empty tubes in total absorbed energy, specific absorbed energy and crush force efficiency. The presence of triggering has no significant effect on total absorbed energy and specific absorbed energy of the empty tubes. However, the crush force efficiency of triggered tube is significantly larger compared to the non-triggered one. In addition, the triggering minimises the force variation of the tubes from the average crush force and in turn a more stable progressive crushing is achieved. The foam-filled and triggered tubes have better crashworthiness than the empty tubes in all the aspects. Compared with either triggered or foam-filled tubes, the triggered and foam-filled tubes have larger values in average crush load and crush force efficiency. In terms of total absorbed energy and specific absorbed energy, the triggered and foam-filled tubes have values always larger than those of the tubes with triggering only, but these values are either larger or smaller than the tubes with foam-filler only.