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A global digital volume correlation algorithm based on higher-order finite elements: Implementation and evaluation
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.ORCID iD: 0000-0001-6663-6536
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
2019 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 168, p. 211-227Article in journal (Refereed) Published
Abstract [en]

We propose a DVC technique that is based on higher-order finite-element discretization of the displacement field and a global optimization procedure. We use curvature penalization to suppress non-physical fluctuations of the displacement field and resulting erroneous strain concentrations. The performance of the proposed method is compared to the commercial code Avizo using trabecular bone images and found to perform slightly better in most cases. In addition, we stress that the performance of a DVC method needs to be evaluated using double scans (zero strain), virtual deformation (imposed deformation) and real deformation. Double scans give insight into the presence of noise and artifacts whereas virtual deformation benchmarks allows evaluation of the performance without noise and artifacts. Investigation of the performance for actual deformed heterogeneous materials is needed for evaluation with noise, artifacts and non-zero strains. We show that both decreasing the resolution of the displacement field (increasing subvolume size) as well as (increasing) curvature penalization (regularization) have a similar effect on the performance of evaluated DVC methods: Decreasing the detrimental effect of noise, artifacts and interpolation errors, but also decreasing the sensitivity of a DVC method to displacement peaks, discontinuities and strain concentrations. The needed amount of regularization is a trade-off between accuracy and precision of the estimated strain fields and their resolution. The obtainable accuracy and precision of the estimated displacement fields are influenced by interpolation errors in the DVC procedure and the relative amount of detail, noise and artifacts in the images. Errors in the displacement field are typically magnified during the strain calculation. Based on the tests and subvolume sizes (16-50 voxels) in this study, the expected order of magnitude of the accuracy and precision is 0.1 micro-voxels and 1 milli-voxels for the displacements and 0.1 and 1 milli-strains of the strain fields. 

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD , 2019. Vol. 168, p. 211-227
Keywords [en]
Digital volume correlation, Accuracy, Precision, Benchmarks, Evaluation, Trabecular bone
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:uu:diva-387714DOI: 10.1016/j.ijsolstr.2019.03.024ISI: 000469906300017OAI: oai:DiVA.org:uu-387714DiVA, id: diva2:1331215
Funder
Swedish Research Council, 2016-04608Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyAvailable from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-08-12Bibliographically approved
In thesis
1. Mechanical analyses of trabecular bone and its interaction with implants
Open this publication in new window or tab >>Mechanical analyses of trabecular bone and its interaction with implants
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bone substitute materials or implants are commonly used in the surgical treatment of bone fractures. However, severe complications are sometimes reported. In order to improve fracture treatment where the interior, porous trabecular bone is involved, it is important to better understand the mechanical properties of this bone and how it interacts with the substitutes/implants, and this was the aim of this thesis.

Since one of the key mechanical properties of trabecular bone, i.e. the elastic moduli at the tissue level, was not consistently reported in the literature, the results from four widely applied methods were first summarized and presented in a review paper.

Furthermore, to improve the analysis of the mechanical behavior of bone and its interaction with implants, a new digital volume correlation (DVC) technique was proposed based on higher-order finite elements.

We further proposed a method to estimate the elastic modulus at the tissue level by compression of single trabeculae within a synchrotron radiation micro-computed tomograph (SRµCT). Full-field displacements were estimated by DVC, which also provided boundary conditions for a finite element model. The proposed method shows potential to estimate trabecular mechanical properties at the tissue level.

Further, strains and cracks of a trabecular structure under compression till fracture were characterized at the single trabecular level, with DVC applied on high-resolution images from SRµCT.

The effect of augmentation materials on the engagement of screws inserted into trabecular bone was evaluated in human femoral bone, with and without real-time SRµCT. A newly developed tissue adhesive indicated a potential benefit of this material to the primary implant stability compared to a cement and no augmentation.

Finally, a trabecular structure of PLA/HA composite material was printed using a fused deposition modelling method as a preliminary step towards better synthetic models of trabecular bone. The synthetic trabecular structure was evaluated using micro-CT, compression and screw pull-out testing.

In conclusion, methods to estimate strains and mechanical properties of trabecular bone were proposed, insights into interactions between trabecular bone and augmentation/implants were gained, as well as a first step towards a synthetic trabecular model, which may contribute to further mechanical analyses and/or improved clinical treatments of trabecular bone.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 65
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1836
Keywords
Trabecular bone, Elastic modulus, Digital volume correlation, Pullout resistance, Micro-computed tomography.
National Category
Other Materials Engineering Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-385143 (URN)978-91-513-0715-2 (ISBN)
Public defence
2019-09-18, Ångström 8001, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2019-08-28 Created: 2019-08-12 Last updated: 2019-09-17

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