Axial collapse behavior of thin-walled stainless-steel circular tubes in diamond mode

As a commonly used axial crushing energy-absorbing component, the theoretical model of the diamond mode of thin-walled circular tubes is less successful than the ring mode. In the experiments, three groups of 304 stainless-steel circular tubes were axially compressed. After validating the numerical model with experimental results, the axial collapse behavior of stainless-steel circular tubes with diameter/thickness ratio D/t  = 50–200 in diamond mode is investigated through both numerical simulation and theoretical analysis in this paper. In numerical simulation, slight initial imperfections are introduced to induce diamond mode collapse with 3–7 circumferential lobes to reveal the folding mechanism of circular tubes in diamond mode and establish the empirical formula about the dimensionless mean crushing stroke of the fold. Based on the experimental and numerical observations, the tube wall's geometric model and energy dissipation mechanism crushing in diamond mode are analyzed theoretically. The maximum circumferential lobes number under different D/t is predicted. A new theoretical model is also proposed to calculate the mean crushing force in diamond mode. The theoretical predictions in this paper achieve good agreement with the numerical and experimental results and show relatively high accuracy.