Stress distribution and fracture propagation in osteons under cyclic torsional loading are the topics of this research which is supported by a POWRE award. Novel experimental data will be obtained in collaboration with the A. Ascenzi research group at "La Sapienza" University in Rome. Samples of fully calcified representative osteon types (longitudinal and alternate osteons) will be isolated and torsionally loaded. Experimentally obtained torque vs angle-of-twist diagrams will be statistically analyzed in terms of stiffness degradation, pinching degradation, and energy absorption. The structural differences between the longitudinal and alternate osteons should correspond to differences in such parameters. Subsequent interpretation in terms of ultrastructural components and observation of fractured samples will form the base for a fracture model. This first fracture micromechanical model allows prediction of the progressive growth of the faulting zones by assessing the increased probability of failure in the vicinity of already cracked regions. This research builds on the PI's recent work on bone microstructural osteons and lamellae. The study will serve as a foundation for the deduction of more realistic non-homogeneous macrostructural mechanical properties of compact bone through lamellar distribution, homogenization methods and finite element analysis. Although sample dimensions render bone microstructural experiments difficult, such microstructural studies allow the discovery of properties, absent in the macrostructure, but nevertheless with fundamental implications for it. Accordingly, this research impacts the study of bone reconstruction and prostheses and pertains to the study of other natural composites as well as the manufacture of new composites. The POWRE award will allow the PI to re-start her academic career after an interruption for family reasons and to redirect her research speciality from mathematics to biomechanics. ***
