This study investigates the mechanical degradation of expanded polystyrene (EPS) foams under repeated compressive loading, with a focus on energy absorption, hysteresis, and efficiency loss. EPS foams of two densities (8.5 kg/m3 and 24 kg/m3) were tested at a loading rate of 500 mm/min, with five cycles for low-density and ten cycles for high-density specimens. Results show a significant reduction in energy absorption capacity after the first cycle: 70% for high-density foams and 60% for low-density. Hysteresis also declined sharply and stabilized within the first few cycles, indicating progressive structural collapse. Efficiency and ideality curves confirmed the irreversible loss of energy recovery capacity. A phenomenological model was proposed to quantify the exponential decay of maximum energy absorption, with parameters dependent on material density and validated by nonlinear regression. Statistical analysis and microstructural characterization using optical and scanning electron microscopy revealed permanent deformation, fracture, and cell elongation after repeated loading. These findings reinforce the non-recoverable nature of EPS under repeated loading in energy dissipation applications and highlight the relevance of predictive modeling and microstructural evaluation for designing more resilient impact-absorbing materials.
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