Orientation Dependent Compressive Response of Human Femoral Cortical Bone as a Function of Strain Rate

Abstract

Under extreme environments, such as a blast or impact event, the human body is subjected to high-rate loading, which can result in damage such as torn tissues and broken bones. The ability to numerically simulate these events would help improve the design of protective gear by iterating different configurations of protective equipment to reduce injuries. Computer codes capable of simulating these events require accurate rate-dependent material models representing the material deformation and failure (or injury) to properly predict the response of human body during simulation. Therefore, the high-rate material response must be measured to allow for simulation of high-rate events. This study seeks to quantify the high-rate mechanical response of human femoral cortical bone for use in high fidelity human anatomical models. Cortical bone compression specimens were extracted from the longitudinal and transverse directions relative to the long axis of the femur from three male donors, ages 36, 43, and 50. The compressive behavior of the cortical bone was studied at quasi-static (0.001/s), intermediate (1/s), and dynamic (~1000/s) strain rates using a split-Hopkinson pressure bar to determine the strain rate dependency and anisotropic effect on the strength of bone. The results indicate that cortical bone is anisotropic and stronger in the longitudinal direction compared to the transverse direction. The human cortical bone compressive response was also rate dependent in both directions, demonstrating significant increase in strength with increase in strain rate. Additionally, as the strain rate increased from intermediate to dynamic, a decrease in the elongation at transverse orientation was observed, which would indicate the bone becomes more brittle.