Mechanical Testing and Material Modelling of Rigid Polyurethane Foam, a Bone Surrogate

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URL: https://hdl.handle.net/1974/31804

Abstract

Rigid polyurethane (PU) foam is an orthopaedic industry standard bone surrogate as it mimics the mechanical behaviour of cancellous bone. It is commonly used for the evaluation of medical implants through Finite Element Analysis (FEA) and mechanical testing. The first objective of this study was to outline methods for testing and evaluation of 20 and 30 pound per cubic foot (PCF) PU foam under uniaxial compression with Digital Image Correlation (DIC) and confined compression, and determine mechanical properties such as Young’s modulus, yield stress, and Poisson’s ratio. The second objective was to develop and calibrate the hyperelastic Ogden material model, for 20 PCF and 30 PCF PU foam, in ABAQUS and perform a sensitivity analysis on a uniaxial compression FEA model. The third objective was to develop and calibrate the crushable foam plasticity (CFP) model, for 20 PCF and 30 PCF PU foam, in ABAQUS and compare results of a uniaxial compression FEA model to uniaxial compression mechanical test data and DIC data. Average Young’s moduli of 20 PCF and 30 PCF PU foam under uniaxial compression were 257±14.2 MPa and 482±37.1 MPa, respectively. Average Young’s moduli of 20 PCF and 30 PCF PU foam under confined compression were 271±5.95 MPa and 456±6.78 MPa, respectively. Three yield stress methods were applied in this study, tangent modulus, plastic strain, and strain gauge method. MannWhitney U tests showed no significant differences between the medians of each of the methods for every test condition and PU foam density. The FEA sensitivity study on a uniaxial compression FEA model with Hyperelastic Ogden material definition resulted in 17.8% and 13.9% stress percent differences between test and FEA results for 20 PCF and 30 PCF PU foam, respectively. Test results from uniaxial compression and confined compression were used in the calibration of the volumetric hardening CFP model for 20 PCF and 30 PCF PU foam. Uniaxial compression FEA models approximated the stress-strain response and axial and transverse strain fields of the mechanical test results. This study found new properties of PU foam and presented new methods for mechanical testing and evaluation. The discussed material models are critical towards validation of numerical models for the preclinical analysis of medical implants with PU foam. Future work should expand on the discussed test methods and sensitivity analyses of presented FEA models.

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Cited By (1)

Year	Entry
2024	Benais R. Computational Modeling of Trabecular Bone Indentation and Development of a New Test Method to Perform Unconstrained Load-Induced Subsidence of an Intervertebral Body Fusion Device [Master's thesis]. University of Waterloo; 2024.