Staggered Fibrils and Damageable Interfaces Lead Concurrently and Independently to Hysteretic Energy Absorption and Inhomogeneous Strain Fields in Cyclically Loaded Antler Bone.

The high toughness and work to fracture of hierarchical composites, like antler bone, involve structural mechanisms at the molecular, nano-, and micro scales, which are not completely explored. A key characteristic of the high energy absorption of such materials is the large hysteresis during cyclic loading, but its origin remains unknown. In situ synchrotron X-ray diffraction tests during tensile loading of antler bone showed heterogeneous fibrillar deformation and hysteresis. To explain the origin of these mechanisms from the nanostructure of antler bone, here we develop a class of finite-element fibril models whose predictions are compared to experimental data across a range of potential composite architectures. We demonstrate that the key structural motif enabling a match to experimental data is an axially staggered arrangement of stiff mineralized collagen fibrils coupled with weak, damageable interfibrillar interfaces.