Development of Rietveld tomography to measure Local Anisotropic Strain and its Application to Bone Nanostructures

Bone and other hierarchically structured materials have unique mechanical properties, which are governed by the spatial arrangement of their nano-constituents. Their structure-mechanics relations can currently be determined down to ~10 µm using X-ray computed tomography. Below this, there is currently no method that can determine local anisotropy of its mechanical properties. This impedes state-of-the-art models from accurately predicting key macroscopic properties such as fracture behaviour. We propose in this project the development of a new method - Rietveld tomography - to determine local anisotropic macro- and micro-strain, based on a new way of analysing X-ray diffraction data that combines the properties of so-called X-ray tensor tomography and Rietveld refinement. The project will consist of the development of the mathematical formulation of Rietveld tomography in the environment of experts in this field at Aarhus Universitet, in particular supervisor Henrik Birkedal; combined with a stay at the secondment institution ESRF, where we will develop the experimental implementation of Rietveld tomography and validate the method. In the third part we will apply the method to osteonal bone and characterize its local response under mechanical load in situ. All that will be implemented and developed in the 24 months of the project, which compiles method development, data analysis strategy development and implementation, and experiments at large-scale synchrotron facilities. We expect that this study will (1) provide a new method to the research community to study not only biominerals but polycrystalline materials in general, linking for the first time hierarchical structure and texture in nanostructured composites. (2) It will lead to a quantum leap in our understanding of bone micromechanics with ensuing impact on bone micromechanical modelling with expected improvements in fracture prediction and ultimately clinical practice in e.g. osteoporosis management.