Application of the Theory of Critical Distances to the notch effect in expanded polystyrene foams

This work studies the notch effect and the influence of particle size on the fracture behavior of Expanded Polystyrene (EPS) foams with U-shaped notches. Two EPS densities, 10 kg/m 3 and 40 kg/m 3 , with average bead sizes of approximately 6 mm and 2 mm, are analyzed. Single Edge Notched Bend (SENB) specimens with notch radii of 1, 2, 4, and 8 mm are tested under three-point bending, alongside unnotched specimens to determine elastic modulus and ultimate tensile strength. Despite EPS’s limited plasticity, consistent fracture parameters are obtained assuming linear elastic behavior. The Theory of Critical Distances (TCD) is applied to predict apparent fracture toughness as a function of notch radius. A pronounced notch effect is observed in low-density EPS (EPS10). The Line Method yields a critical distance of about 3.8 mm, close to the bead size, indicating fracture is governed by interparticle decohesion and microstructural features. High-density EPS (EPS40) shows no significant notch effect, suggesting a more complex crack propagation involving fused particle clusters, reducing sensitivity to geometric stress concentration. These results demonstrate the combined influence of particle size, notch geometry, and microstructure on the mechanical response of EPS foams.