Mechanical properties and multi-objective optimization of reinforced re-entrant honeycomb sandwich structures under bending load

Overview

This study introduces a catenary-reinforced re-entrant honeycomb (RRH) sandwich beam designed to enhance crashworthiness and energy absorption under bending loads. Re-entrant honeycomb structures exhibit negative Poisson's ratio effects and hollow structural characteristics that limit their load-bearing capacity. The catenary reinforcement method addresses these limitations by constraining rotational deformation of inclined cell walls around vertices and exploiting the load-bearing efficiency inherent to catenary geometries. The research investigates mechanical properties through experimental testing and parametric analysis, followed by multi-objective optimization to improve structural performance metrics including maximum load-bearing force, energy absorption, and mass efficiency.

Methods and approach

Metallic specimens of the proposed RRH sandwich beam structure were fabricated and subjected to three-point bending tests to evaluate mechanical performance. A parametric analysis examined the influence of facesheet and core thickness parameters on deformation behavior and energy absorption characteristics. Multi-objective optimization was performed using the thicknesses of front facesheet, back facesheet, and core as optimization variables. The optimization targeted three objectives: mass, maximum load-bearing force, and energy absorption. Comparative analysis was conducted between the proposed RRH sandwich beams and conventional honeycomb sandwich beams under both in-plane and out-of-plane loading conditions, with comparisons made at identical wall thickness and mass to ensure valid performance benchmarking.

Results

Experimental results demonstrated that the catenary reinforcement structure effectively limits rotational deformation of inclined cell walls around vertices. The load-bearing force drop following initial plastic deformation was reduced from 29.3% to 6.6% compared to unreinforced configurations. Relative to classical re-entrant honeycomb cored beams, the RRH sandwich beams exhibited improvements of 26.7% in maximum load-bearing force and 8.9% in energy absorption. Parametric analysis confirmed that front facesheet, back facesheet, and core thickness significantly affect deformation behavior and energy absorption. The optimized sandwich beam configuration achieved performance increases of 64.9% in maximum load-bearing capacity and 46.9% in energy absorption. Comparative analysis demonstrated superior energy-absorbing protective performance of the RRH sandwich beams relative to conventional honeycomb sandwich structures.

Implications

The catenary reinforcement method represents a viable approach for enhancing the structural performance of re-entrant honeycomb sandwich beams, particularly in applications requiring improved crashworthiness and energy absorption. The demonstrated reductions in post-yield load drop and substantial improvements in load-bearing capacity suggest potential applications in protective structural systems and impact-resistant components. The parametric and optimization frameworks established in this research provide systematic design guidance for honeycomb core sandwich beam reinforcement, enabling tailored configurations based on specific performance requirements. The superior performance of RRH sandwich beams under both in-plane and out-of-plane loading conditions indicates broader applicability across diverse loading scenarios in structural engineering applications.