Thin-walled energy absorbers are widely used in transportation systems to mitigate damage during low-speed collisions an‎d enhance safety by dissipating kinetic energy through plastic deformation occurring during folding an‎d structural changes. To further improve crashworthiness, auxetic metamaterials, which are generally engineered structures with negative effective Poisson’s ratios, have recently gained attention due to their superior energy absorption, indentation resistance, an‎d crack growth suppression. This study focuses on investigating the crashworthiness an‎d developing metallic auxetic energy absorbers with thin-walled cross-sections. For this purpose, auxetic behavior was induced in conventional thin-walled sections with positive Poisson’s ratio by introducing a specific arrangement of perforations. Numerical simulations in Abaqus/Explicit were used to analyze the mechanical responses an‎d crashworthiness of the proposed structures under quasi-static conditions. For accurate numerical analysis, uniaxial tensile test data of AISI 316L coupons were first organized an‎d reproduced using constitutive laws. Subsequently, through finite element simulations of the tensile test in Abaqus, the parameters of the ductile damage model were calibrated via the Jia–Kuwamura method. Next, the model was verified by simulating a uniaxial compression test on a thin-walled structure for which experimental data are available in the literature. The final calibration demonstrated that the proposed procedure for preparing input data an‎d the overall process is sufficiently accurate for quasi-static simulations of auxetic thin-walled structures under compressive loading, successfully predicting their mechanical responses an‎d deformation patterns. The models examined included three shell forms: cylindrical, conical, an‎d corrugated, each combined with five induced microstructures at pattern scaling factors (PSF) ranging from 0% to 40%. The microstructures were geometric modules with elliptical perforations whose aspect ratios were determined by a regression function λ(PSF), plus one case with a natural form obtained from finite element analysis. After performing the simulations, the performance of each absorber was compared with other members of the same category, while the cylindrical structure with circular perforations (PSF 0%) was used as the global reference. This study not only improved the general understan‎ding of the crashworthiness of thin-walled structures with buckling-induced microstructures but also introduced two new categories of thin-walled structures with auxetic properties, which effectively enhance crashworthiness. The first category is auxetic conical shells, where in the best-obtained configuration with an apex angle of 4° an‎d a microstructure with PSF = 20%, the specific energy absorption (SEA) increased by 2.13 times, the crash force efficiency (CFE) by 1.83 times, an‎d the initial peak crushing force (IPCF) decreased by 12.1%, compared to the reference cylindrical model. The second category is auxetic corrugated shells, where in the best case with six corrugations an‎d the same microstructure, the CFE improved by 2.21–2.80 times (depending on the calculation method), IPCF decreased by 61%, an‎d SEA increased by 8.5%. Among the cylindrical models, introducing auxetic behavior from the beginning of loading increased SEA by 18.9%, raised CFE by 2.33 times, an‎d reduced IPCF by 45%. Although increasing wall thickness intensified the auxetic effect in this group, it led to a reduction in crashworthiness indexes. Employing microstructures with variable void fraction showed that, although this approach can enhance general stability an‎d tune the intensity of auxetic behavior, it is not necessarily suitable for improving crashworthiness. Additionally, the microstructure with a 20% scale factor was found to exhibit the best performance when combined with various shell shapes.

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عليرضا سلجوقيان , محسن ابوطالبي اصفهاني