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<p>The growing development of innovative sandwich structures utilizing auxetic metamaterials with improved mechanical properties has enabled a more effective balance between strength and lightweight design in demanding applications, such as aerospace and aeronautical shells, which often feature complex curved geometries subjected to extreme loading conditions and destabilizing forces. With the primary objective of improving the thermomechanical stability of lightweight shells under complex loadings, this work investigates the nonlinear stability of sandwich toroidal shell segments (TSSs) with an auxetic core and carbon nanotube (CNT)-reinforced face sheets. The TSSs, supported by the Kerr foundation, are subjected to combined thermomechanical loading, including axial compression, radial pressure, and thermal effects. The thermal conditions considered include uniform temperature rise and linear or nonlinear gradients across the shell thickness. CNTs are embedded within the temperature-dependent polymer matrix in the face sheets. A novel star-shaped auxetic metamaterial is proposed as the core in the sandwich structure, which provides significant advantages over conventional re-entrant auxetic cellular structures. The governing equations are derived within the framework of Reddy's third-order shear deformation theory (TSDT) and von Kármán-type geometric nonlinearity, and the Galerkin method is used to solve the nonlinear equations. Model validation through comparison with existing studies confirms its high accuracy. Numerical analyses demonstrate the greater effectiveness of the star-shaped auxetic core compared to conventional re-entrant auxetic structures, with critical buckling loads reaching up to 16.07% improvement in thicker shells under elevated thermal loading, highlighting its advantages in a lightweight metamaterial TSS design. Through a comprehensive parametric study, the effects of key geometric parameters of the star-shaped auxetic core on the effective properties of the lattice metamaterial structure are investigated. The study also examines the influence of various combined thermomechanical loading conditions, shell geometric parameters, and Kerr foundation properties on critical buckling loads and postbuckling paths. The results demonstrate that by properly selecting the auxetic core's geometric parameters, auxeticity can be tailored while achieving higher stiffness in the lattice structure to meet diverse application requirements.</p>

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Thermomechanical stability enhancement in sandwich composite toroidal shells utilizing star-shaped auxetic core

  • 期刊论文

  • 发表日期：

    2025年8月30日

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  • Farzad Ebrahimi,
  • Mohammadhossein Goudarzfallahi,
  • Ali Alinia-ziazi

摘要

The growing development of innovative sandwich structures utilizing auxetic metamaterials with improved mechanical properties has enabled a more effective balance between strength and lightweight design in demanding applications, such as aerospace and aeronautical shells, which often feature complex curved geometries subjected to extreme loading conditions and destabilizing forces. With the primary objective of improving the thermomechanical stability of lightweight shells under complex loadings, this work investigates the nonlinear stability of sandwich toroidal shell segments (TSSs) with an auxetic core and carbon nanotube (CNT)-reinforced face sheets. The TSSs, supported by the Kerr foundation, are subjected to combined thermomechanical loading, including axial compression, radial pressure, and thermal effects. The thermal conditions considered include uniform temperature rise and linear or nonlinear gradients across the shell thickness. CNTs are embedded within the temperature-dependent polymer matrix in the face sheets. A novel star-shaped auxetic metamaterial is proposed as the core in the sandwich structure, which provides significant advantages over conventional re-entrant auxetic cellular structures. The governing equations are derived within the framework of Reddy's third-order shear deformation theory (TSDT) and von Kármán-type geometric nonlinearity, and the Galerkin method is used to solve the nonlinear equations. Model validation through comparison with existing studies confirms its high accuracy. Numerical analyses demonstrate the greater effectiveness of the star-shaped auxetic core compared to conventional re-entrant auxetic structures, with critical buckling loads reaching up to 16.07% improvement in thicker shells under elevated thermal loading, highlighting its advantages in a lightweight metamaterial TSS design. Through a comprehensive parametric study, the effects of key geometric parameters of the star-shaped auxetic core on the effective properties of the lattice metamaterial structure are investigated. The study also examines the influence of various combined thermomechanical loading conditions, shell geometric parameters, and Kerr foundation properties on critical buckling loads and postbuckling paths. The results demonstrate that by properly selecting the auxetic core's geometric parameters, auxeticity can be tailored while achieving higher stiffness in the lattice structure to meet diverse application requirements.