Thesis-2013-LiOA.pdf (18.27 MB)
Cutting of cortical bone tissue: analysis of deformation and fracture process
thesis
posted on 2013-10-22, 08:17 authored by Simin LiCortical bone tissue – one of the most intriguing materials found in nature –
demonstrate some fascinating behaviours that have attracted great attention
of many researchers from all over the world. In contrast to engineering
materials, bone has its unique characters: it is a material that has both
sufficient stiffness and toughness to provide physical support and protection
to internal organs and yet adaptively balanced for its weight and functional
requirements. Its structure and mechanical properties are of great importance
to the physiological functioning of the body. Still, our understanding on the
mechanical deformation processes of cortical bone tissue is rather limited.
Penetration into a bone tissue is an intrinsic part of many clinical procedures,
such as orthopaedic surgery, bone implant and repair operations. The
success of bone-cutting surgery depends largely on precision of the
operation and the extent of damage it causes to the surrounding tissues. The
anisotropic behaviour of cortical bone acts as a distinctive protective
mechanism and increases the difficulty during cutting process. A
comprehensive understanding of deformation and damage mechanisms
during the cutting process is necessary for improving the operational
accuracy and postoperative recovery of patients. However, the current
literature on experimental results provides limited information about
processes in the vicinity of the cutting tool-bone interaction zone; while;
numerical models cannot fully describe the material anisotropy and the effect
of damage mechanisms of cortical bone tissue. In addition, a conventional
finite-element scheme faces numerical challenges due to large deformation
and highly localised distortion in the process zone.
This PhD project is aimed at bridging the gap in current lack of understanding
on cutting-induced deformation and fracture processes in the cortical bone
tissue through experimental and numerical approaches.
A number of experimental studies were accomplished to characterise the
mechanical behaviour of bovine cortical bone tissue and to analyse
deformation and damage mechanisms associated with the cutting process
II
along different bone axes in four anatomic cortices, namely, anterior,
posterior, medial and lateral. These experiments included: (1) a Vickers
hardness test to provide initial assessments on deformation and damage
processes in the cortical bone tissue under a concentrated compressive load;
(2) uniaxial tension and compression tests, performed to understand the
effect of orientation and local variability of microstructure constituents on the
macroscopic material properties of cortical bone; (3) fracture toughness tests,
aimed at elucidating the anisotropic character of fracture toughness of
cortical bone and its various fracture toughness mechanisms in relation to
different orientations; (4) penetration tests, conducted to evaluate and
validate mechanisms involved in bone cutting as well as orientation
associated anisotropic deformation and damage processes at various
different cortex positions. Information obtained in these experimental studies
was used to assist the development of advanced finite-element models: (1)
the effective homogenised XFEM models developed in conjunction with
three-point bending test to represent a macroscopically, anisotropic elasticplastic
fracture behaviour of cortical bone tissue; (2) three microstructured
XFEM models to further investigate the effect of the randomly distributed
microstructural constituents on the local fracture process and the variability of
fracture toughness of cortical bone; (3) a novel finite-element modelling
approach encompassing both conventional and SPH elements, incorporating
anisotropic elastic-plastic material properties and progressive damage criteria
to simulate large deformation and damage processes of cortical bone under
penetration. The established models can adequately and accurately reflect
large deformations and damage processes during the penetration in bone
cutting.
The results of this study made valuable contributions to our existing
understanding of the mechanics of cortical bone tissue and most importantly
to the understanding of its mechanical behaviours during the cutting process.
Funding
EPSRC
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© Simin LiPublication date
2013Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University. This is the open access version of the thesis with images removed.Language
- en