A bio-inspired fractal multi-cell circular (BFMC) tube with embedded regular polygons is proposed to address the gap between the need for high absorption and the limited performance of traditional thin-walled circular tubes. Inspired by biological structures and fractal hierarchy theory, geometric models of BFMC tubes embedded with square, pentagonal, and hexagonal cells are constructed. Numerical simulations are carried out to systematically investigate the effects of mass, fractal dimension, and the number of sides of the embedded polygons on the axial crushing performance, and the results are compared with those of typical multi-tubes. The results indicate that, under approximately equal mass conditions, the BFMC tube can significantly enhance the specific energy absorption and the load-bearing capacity owing to its fractal hierarchical and bio-inspired configurations. Its crashworthiness increases with mass, first decreases and then rises as the fractal dimension increases, and improves further as the number of polygon sides increases, while the peak force is only weakly affected. A theoretical model for predicting the mean crushing force of BFMC tubes is developed based on the super folding element theory and is validated through numerical simulations. This study provides theoretical support and structural design guidelines for developing high performance thin-walled energy absorption structures.

To enhance the prediction accuracy of low-velocity impact performance and improve the structural design efficiency of triangular corrugated sandwich beams, this paper proposes a machine learning modeling and optimization process for the impact response of sandwich beams based on a hard-parameter-sharing multi-task learning (MTL) framework. A sample dataset is generated using finite element models, and the rationality of the models is validated against existing experimental results. Subsequently, an MTL model is trained to simultaneously predict the structural specific energy absorption (SEA), the maximum deflection of the top panel, and the initial peak load. The results show that the MTL model optimized via Bayesian optimization demonstrates strong predictive performance under a 50 J impact energy condition. The predictions align well with the finite element simulation results, with the coefficient of determination R² for all output variables in the test set exceeding 0.989, thereby validating the effectiveness and reliability of the model in response prediction and engineering optimization analysis. Parameter sensitivity analysis reveals that the core cell count and core wall thickness have the most significant influence on structural stiffness, followed by the top panel thickness, while the bottom panel thickness has a relatively minor impact. Moreover, the core wall thickness exhibits a certain saturation threshold in terms of performance enhancement. In combination with the non-dominated sorting genetic algorithm Ⅱ (NSGA-Ⅱ), multi-objective optimization analysis are conducted focusing on deformation characteristics, energy absorption performance, and comprehensive performance, and yields optimal parameter configurations that meet different engineering design requirements for sandwich beams.

The dynamic response and energy absorption performance of foam aluminum sandwich tubes under lateral explosive loads were systematically investigated using a combination of experimental research and numerical simulation. A series of lateral explosion experiments were conducted using a ballistic pendulum system to analyze the effects of structural geometric parameters, foam aluminum density, and the explosive mass on the deformation mode and blast resistance performance. Based on the experimental results, numerical simulations were performed to further compare the blast resistance performance of foam aluminum sandwich tubes and circular tube core sandwich tubes, comparing gradient and non-gradient designs of circular tube core sandwich tubes. The results show that, the final deformation of circular tube core sandwich tubes is greater than that of foam aluminum sandwich tubes, although the difference is not significant. Among the gradient circular tube core sandwich tubes, the configuration with the largest outer wall thickness and the thinnest middle layer exhibits the best improvement in blast resistance performance. Furthermore, the blast resistance performance of gradient circular tube core sandwich tubes is significantly superior to that of non-gradient structures.