Publication: Finite element analysis of deformation and fracture of cortical bone in vibration-assisted bone cutting
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Date
2024-11-01
Authors
Du, Qianrui
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Abstract
The use of vibration-assisted cutting (VAC) technology has made its way from
industrial applications to the medical field, particularly in bone cutting for orthopaedic
surgery. Nevertheless, the bone cutting process can be quite complex because of the
bone’s anisotropic properties, which contribute to its intrinsic toughening mechanism
and vulnerability to surface damage. Therefore, it is important to take into account the
impact of microstructure on the efficiency of the bone cutting process, which can be
accurately evaluated using the finite element method. Yet, simulating tool-bone
contact is seldom done because of the large deformation of the bone model, which can
cause convergence issues, thereby adding complexity to the analysis. Hence, to
simplify the modelling process, this study creates Python code for building a bone
micro-model that includes bone microstructure considerations. The code allows for
creating a micro-model with a user-defined distribution of bone microstructure
constituents, enabling adjustable porosity. Two bone models with different
microstructure properties and porosity are created using the code to represent young
and aged bones. The models have been validated through a comparison of the stress
intensity factor with the analytical results for a single-edge notch bending (SENB)
specimen, revealing a deviation of just 4.5%. By incorporating the extended finite
element method (XFEM), these models are utilised to analyse how amplitude and
cutting depth impact the performance of vibration-assisted bone cutting. This analysis
involves quantitatively assessing the resulting cutting force, stress, strain rate, crack
initiation and propagation, and comparing them to conventional cutting methods. According to the results, VAC consistently decreases cutting force and stress in both
models for various cutting depths and shows improved control of crack extension
direction with smoother crack curves. It has been noted that the impact of amplitude
variation on the resulting cutting force varies between the two models. In aged bones,
increasing the amplitude decreases the cutting force, whereas in young bones, it has a
negligible effect. In terms of bone strain rate, vibration-assisted cutting can
significantly increase the cutting strain rate, thus reducing toughness damage and
cumulative damage. VAC temperature is observed to be higher than conventional
cutting. At the area of high temperature, which is near the tool, the cutting chips are
smaller.