Shock absorber with inward-folding composite tube and its application in legged landing gear

A shock absorber based on the progressive failure of a composite tube was developed. The composite tube is subjected to axial compression from the pressing cap at one end and folds inward at the other end under the effect of the crush cap without debris overflow. The crushed composite is compacted into a hollow tube and increases the resisting force once it reaches the pressing cap. For larger strokes without a load increase, a hole is made in the pressing cap for the crushed composite. Three crush caps with different curvatures of the inward-folding surface and two composite tubes were evaluated through static and dynamic tests. The crush cap lowered the initial peak load and varied the specific energy absorption (SEA). We also investigated the effects of connection rivets. Aluminum rivets were severed and had little effect on the load curve while steel rivets did not shear but cut the composite tube into strips, resulting in a lower sustained load because failure was induced. A set of shock absorbers with larger strokes was tested for use in the legged landing gear of a drone assumed to crash with a speed of 10 m/s, energy of 5000 J, and overload of less than 25 g. The maximum SEA of the absorbers, including the two caps, was 20 kJ/kg.