Crashworthiness of Thin-Walled Square Steel Columns Reinforced Based on Fractal Geometries

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In this paper, the crashworthiness of steel thin-walled square columns was investigated. These structures were reinforced with three types of reinforcers. The first type was aluminum shells which were placed inside the steel columns based on a specific fractal geometry, and two other types were aluminum and polyurethane foams. All samples were placed under axial loading, and fractals were thinned out up to three stages. At each stage, the effectiveness of aluminum shells alone and also in the presence of polyurethane and aluminum foams has been investigated. Also, the effect of foams' location and in or out of fractal geometry, was studied. The results showed that the presence of reinforcers with different geometries and materials improved the energy absorption. As the fractal geometry of the reinforcers becomes smaller, the energy absorption capacity increases. The presence of the foams well compensated the load–displacement diagram drop after the initial peak and made the energy absorption behavior more ideal. On the other hand, polyurethane foam showed a significant effect on buckling control so that in one of the samples it prevented buckling. Comparison of the studied samples showed that the energy absorption was better when polyurethane foam prevailed. The effect of the second-stage fractal geometry was almost twice the fractal geometry of the first stage. The best choice among the discussed examples was an absorbent in the second stage with foam, in which the polyurethane foam predominated. Finally, some results were validated.