A Method for Evaluation the Fatigue Microcrack Propagation in Human Cortical Bone Using Differential X-ray Computed Tomography.

Petr Koudelka,Jan Sleichrt,Michal Vopalensky,Vaclav Rada,Tomas Fila,Pavel Benes,Vendula Bendova,Daniel Kytyr,Petr Zlamal,Ivana Kumpova

doi:10.3390/ma14061370

Petr Koudelka, Jan Sleichrt + Show 8 more

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https://doi.org/10.3390/ma14061370

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Abstract

Fatigue initiation and the propagation of microcracks in a cortical bone is an initial phase of damage development that may ultimately lead to the formation of macroscopic fractures and failure of the bone. In this work, a time-resolved high-resolution X-ray micro-computed tomography (CT) was performed to investigate the system of microcracks in a bone sample loaded by a simulated gait cycle. A low-cycle (1000 cycles) fatigue loading in compression with a 900 N peak amplitude and a 0.4 Hz frequency simulating the slow walk for the initialization of the internal damage of the bone was used. An in-house developed laboratory X-ray micro-CT imaging system coupled with a compact loading device were employed for the in situ uni-axial fatigue experiments reaching a effective voxel size. To reach a comparable quality of the reconstructed 3D images with the SEM microscopy, projection-level corrections and focal spot drift correction were performed prior to the digital volume correlation and evaluation using differential tomography for the identification of the individual microcracks in the microstructure. The microcracks in the intact bone, the crack formation after loading, and the changes in the topology of the microcracks were identified on a volumetric basis in the microstructure of the bone.

Highlights

As a part of the research devoted to the damage and remodeling of a human cortical bone, the processes and mechanisms related to the influence of imperfections and the fracture characteristics have been intensively studied [1]
The alignment of the volumes was performed using the transformation determined by the digital volume correlation (DVC), while only the microcracks not originating from the surface of the mechanically and thermally affected sample during the preparation are highlighted and taken into account
This is an expected result conforming to the fundamentals of fracture mechanics, it is an important finding that the regions of stress concentration with the presence of a system of microcracks were clearly apparent in the displacement field of the full-affine DVC procedure

Summary

Introduction

As a part of the research devoted to the damage and remodeling of a human cortical bone, the processes and mechanisms related to the influence of imperfections and the fracture characteristics have been intensively studied [1]. An engineering analogue of a cortical bone is a fibre-reinforced composite, where, during the fatigue loading, both phases allow the formation of matrix damage and energy dissipation at the microstructural interfaces that limit the microcrack propagation. As a result of aging or disease-induced remodeling, a sustained loading at levels excessive for damage tolerance of the bone causes unlimited microcrack propagation, which may result in a microdamage accumulation together with a loss of tissue heterogeneity and a reduction of its macroscopic fracture toughness [4,5]

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