A Polyurethane Foam Bone Analogue Material Model for Computational Simulations: Calibration, Validation, and the Impact of Crushable Foam Yield Stress Ratio

Rigid polyurethane (PU) bone foam is widely used in biomechanical experiments and simulations, making accurate characterization of its material properties crucial for developing reliable models. However, there is currently no publicly available calibrated and validated material model for PU bone foam that is practical across different loading states. This study aimed to develop and validate an open-source material model for PU bone foam. We utilized in-house data from uniaxial compression, laterally confined compression, and tensile tests, as well as shear test data provided by the manufacturer, to inform the material model parameters for transversely isotropic elasticity, crushable foam plasticity, and ductile damage initiation and evolution in finite element (FE) simulations. The material model was tested in simulations of shear, compression, screw pullout, and spinal cage subsidence tests. Validation results showed good agreement with experimental data, with nearly all outputs of interest falling within one standard deviation of the mean experimental values. The effect of varying the crushable foam yield stress ratio (k) was also investigated. Increasing the k value resulted in decreased compressive strength in the compression test, a reduction in subsidence yield load, and an increase in shear strength. Changing k had no clear effect on pullout force.