Effect of strain rate on the mechanical properties of human ribs: Insights from complete rib bending tests

Abstract

This study reassesses the mechanical properties of cortical bone by conducting complete rib bending tests to evaluate the effect of strain rate ($0.0005<\dot{\varepsilon }<0.50$) on key mechanical parameters. The research involved $n=12$ specimens, divided into balanced groups based on age and strain rate. Unlike the traditional approach, which relies on tensile testing of machined cortical bone fragments, this methodology uses intact ribs subjected to bending, eliminating the need for extensive preparation through machining, and determine the mechanical properties in this test in an accurate computational manner.

Complete rib bending tests pose unique challenges compared to uniaxial tensile tests. The ribs’ curved shape and variable cross-sections necessitate the application of finite strain theory to accurately measure deformation, accounting for large displacements. This study aims to (1) validate the feasibility of deriving precise mechanical properties directly from intact bones, and (2) confirm that these results align with those from tensile testing, which, although simpler to execute, require greater preparation efforts.

The findings from the rib bending tests confirm the following: (1) the Young’s modulus of cortical bone decreases with age but remains largely unaffected by strain rate within the range examined; and (2) both maximum strain and maximum stress decline with age but increase with higher strain rates. While these trends were previously observed in tensile tests, this study provides new evidence using the more complex methodology of complete rib bending, and describes the progressive loss of stiffness with damage models.