Mechanical and Vibration Performance of Novel Lightweight Sandwich Structures with EPS Beads Filled Syntactic Foam Cores

This study introduces a new class of lightweight sandwich composites featuring syntactic foam cores filled with expanded polystyrene (EPS) beads and reinforced by single-layer glass fiber-reinforced polymer (GFRP) face sheets. The hybrid core structure was formulated by embedding hollow glass microballoons (HGMs) and EPS beads of varying densities (10, 18, and 30 kg/m3) into an epoxy matrix, enabling precise control over core morphology and mechanical behavior. The structural performance was comprehensively evaluated through uniaxial compression, three-point bending, and free vibration tests. To complement the experimental investigations, a finite element model based on third-order shear deformation theory was developed to simulate the vibrational response. The model exhibited strong agreement with experimental data, confirming its predictive accuracy. Results reveal that increasing EPS bead density significantly enhances the core and overall composite density, leading to improved compressive and flexural strengths, elevated natural frequencies, and reduced damping capacity. Notably, the sandwich architecture dramatically boosted the flexural load-bearing capacity of the syntactic coresachieving up to a 5-fold improvement over the standalone core materials. These findings underscore the effectiveness of EPS bead-filled syntactic foams in tailoring the mechanical and dynamic properties of sandwich composites. The proposed design strategy offers a scalable and versatile approach for developing lightweight structural components with enhanced performance, suitable for demanding aerospace, automotive, and marine applications.