Functionally graded and non-convex tubes usually present superior crashworthiness performance. Therefore, functionally graded non-convex tubes (FGNTs) may perform superior energy absorption. Nevertheless, no theoretical approach has been conducted to predict the crashworthiness characteristic of FGNTs under axial impact. As a result, the micro-element-based theoretical prediction method is conducted to predict the crashworthiness response of FGNTs in this paper. Theoretical models are illustrated for various corner-shaped elements along the FGNT. There are two deformation processes for the constituent elements: membrane and bending. Consequently, the theoretical solutions for the bending and membrane components are developed separately. The crashworthiness response of FGNTs with 12, 20, and 28 corners are analyzed, followed by a comparison of the numerical and theoretical results to validate the proposed theories. The results indicate that the proposed theory could accurately predict the FGNTs’ crashworthiness performance. This study offers a pragmatic method for forecasting the crashworthiness behavior of FGNTs under axial loads.
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