Characterization of PMHS Ribs: A New Test Methodology

This paper presents the results of structural tests to investigate, first, the relationships between geometric and constitutive characteristics of ribs and, second, their mechanical behaviour and rupture threshold. A new methodology was developed that included tests on complete isolated ribs. These tests simulated anterior-posterior loading, as seen in frontal impact. The 4(th) to 9(th) ribs were removed from five cadaver rib cages. The costal geometry was obtained from CT scans and was used to build a specific finite-element model for each rib tested. The test set-up was composed of two caps wherein the two rib extremities were potted. One cap was fixed on the frame of the test set-up through a pin joint. The second cap was fixed to a mobile truck through a pin joint. The truck allowed low friction translation along the anterior-posterior axis. Translation was imposed on the cap such that a constant displacement rate was obtained. External forces and moments were recorded by a sensor at the spinal end. The rotational displacements on the sternal and spinal ends and the translational displacement of the truck were recorded. The mineral content of the ribs was also measured. Fracture was found to occur at a mean displacement of 41 mm, at a mean rupture load of 87 N, and at a mean stiffness of 2340 N/m. Three ribs were reconstructed in a finite-element model and the test set-up was simulated. Comparisons between tests and simulations are provided and discussed.