Crashworthy subfloor structure with shock absorbers using fixed-to-hinged transforming joints and inward-folding composite tube filled with foam

Abstract

A shock absorber characterised by fixed-to-hinged transforming joints and inward-folding composite tubes was demonstrated for the first time. Polymethacrylimide foam can be filled into the composite tube to enhance energy absorption. A pair of shock absorbers were installed in the subfloor structure as stanchions. The shock absorber, inclined at an angle to the impact direction, was joined to the subfloor structure with five fasteners arranged so that one is in the centre and the others around it. The five fasteners bore a static load during normal operations. During the crash, the eccentric load is exerted on the shock absorber as the crushing of the composite tube; then, the surrounding fastener is served, with the central fastener left as a pin. Hence, the fixed joint is transformed into a hinged joint, making the shock absorber only subject to an axial load, and a large crush ratio for the absorber is available. A method to calculate the crash load of a subfloor structure was demonstrated. Experiments were conducted using a drop tower, which verified the schematic and crash-load calculations. The results also show that the specific energy absorption of the composite tube filled with foam is improved. The proposed schematic of the subfloor structure has the potential for use as an aircraft cargo floor.