Investigation of Size Effect and Compressive Failure Mechanism in Rigid Polyurethane Foam Under Uniaxial Compression Using CT Scanning Technology

The absence of standardized specimen dimensions for uniaxial compression tests and the unclear compressive failure mechanism of rigid polyurethane foam (RPUF) as a backfill material remain significant challenges. This study investigates the compressive failure mechanisms of two RPUF types by employing X‐ray computed tomography (CT) and scanning electron microscopy (SEM). The optimal specimen size for uniaxial compression tests was determined to be a cylinder with a diameter of 87 mm, height of 50 mm, and a height‐to‐diameter ratio of 0.57. CT‐based 3D reconstruction revealed crack propagation paths and porosity distribution, while SEM analysis elucidated the relationship between pore morphology and fracture mechanisms. The results indicate that after compression, RPUF‐IM exhibited brittle fracture with significant pore anisotropy, where the longitudinal equivalent pore diameter was 2.5 times larger than the transverse diameter, predisposing it to localized collapse. In contrast, RPUF‐DS demonstrated plastic deformation capability, with a mere 10%–20% increase in longitudinal equivalent porosity compared to the transverse direction. Post‐compression, pore closure and an increase in the proportion of smaller pores were observed in RPUF‐DS, contributing to its superior mechanical performance. This study provides a theoretical and experimental basis for the engineering application of RPUF as a backfill material.