Thesis-2013-Chakraborty.pdf (4.86 MB)
Download fileTomographic measurement of all orthogonal components of three-dimensional displacement fields within scattering materials using wavelength scanning interferometry
thesis
posted on 2013-11-04, 09:11 authored by Semanti ChakrabortyExperimental mechanics is currently contemplating tremendous opportunities of further
advancements thanks to a combination of powerful computational techniques and also fullfield
non-contact methods to measure displacement and strain fields in a wide variety of
materials. Identification techniques, aimed to evaluate material mechanical properties given
known loads and measured displacement or strain fields, are bound to benefit from increased
data availability (both in density and dimensionality) and efficient inversion methods such as
finite element updating (FEU) and the virtual fields method (VFM). They work at their best
when provided with dense and multicomponent experimental displacement (or strain) data,
i.e. when all orthogonal components of displacements (or all components of the strain tensor)
are known at points closely spaced within the volume of the material under study. Although a
very challenging requirement, an increasing number of techniques are emerging to provide
such data.
In this Thesis, a novel wavelength scanning interferometry (WSI) system that provides three
dimensional (3-D) displacement fields inside the volume of semi-transparent scattering
materials is proposed. Sequences of two-dimensional interferograms are recorded whilst
tuning the frequency of a laser at a constant rate. A new approach based on frequency
multiplexing is used to encode the interference signal corresponding to multiple illumination
directions at different spectral bands. Different optical paths along each illumination direction
ensure that the signals corresponding to each sensitivity vector do not overlap in the
frequency domain. All the information required to reconstruct the location and the 3-D
displacement vector of scattering points within the material is thus recorded simultaneously
in a single wavelength scan. By comparing phase data volumes obtained for two successive
scans, all orthogonal components of the three dimensional displacement field introduced
between scans (e.g. by means of loading or moving the sample under study) are readily
obtained with high displacement sensitivity.
The fundamental principle that describes the technique is presented in detail, including the
correspondence between interference signal frequency and its associated depth within the
sample, depth range, depth resolution, transverse resolution and displacement sensitivity.
Data processing of the interference signal includes Fourier transformation, noise reduction,
re-registration of data volumes, measurement of the illumination and sensitivity vectors from
experimental data using a datum surface, phase difference evaluation, 3-D phase unwrapping and 3-D displacement field evaluation.
Experiments consisting of controlled rigid body rotations and translations of a phantom were performed to validate the results. Both in-plane and the out-of-plane displacement components were measured for each voxel in the resulting data volume, showing an excellent agreement with the expected 3-D displacement.
Funding
Loughborough University and EPSRC
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© Semanti ChakrabortyPublication date
2013Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en
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Keywords
Experimental mechanicsNon-contact methodsDisplacement and strain fieldsInversion methodsWavelength scanning interferometryFrequency multiplexingSensitivity vectorsPhase volumesDepth rangeDepth resolutionTransverse resolutionDisplacement sensitivityData processingFourier transformationRe-registrationMechanical Engineering not elsewhere classified