Measurements of deformations and flows inside optically nontransparent materials
Abstract: When a material is mechanically loaded or experience environmental changes such as for example thermal or pressure variations it is affected, in some way, due to these new conditions. In order to measure engineering properties related to these structural changes, such as for example deformation and strain, we need to gain information about them that are precise and reliable. There exist many different methods for such measurements. However, most often these methods measure the pure surface response due to the deforming mechanism, since this is what can be observed directly by use of cameras and various sensors. We therefore know a lot about how the material surface behaves but not much about how the structure beneath the surface behaves. As long as the material structure is reasonably homogeneous this may be enough but as the complexity of the material structure increase it gets more important to obtain information from the inside of the material. In this thesis two techniques with the ability to measure internal deformations in optically non-transparent materials are presented. The fundamental principle of both the techniques is the same. The techniques utilize a correlation based routine to estimate deformations from two and three dimensional image data collected with x-ray-based methods. The first technique, called Digital Speckle Radiography (DSR), measures two-dimensional deformation fields, in a single plane within the examined material. The deformations are estimated by the use of image correlation applied to two-dimensional digital x-ray images. The second technique, called Tomographic 3D-DSP, measures the three-dimensional unrestricted deformation, in every point of the examined object. Here the correlation procedure is carried out on volumetric object data collected with computed tomography (CT). Three separate experiments have been carried out, to investigate the behaviour of the two techniques. In two of the experiments the two-dimensional technique is applied. In the first of these the flow profile of an alumina powder is measured as it flows through a silo configuration. In the second experiment the motion in a thin film of glue, sandwiched between two wooden plates, exposed to shear, is measured. Finally in the third experiment the three-dimensional technique is used to measure the deformations in bone tissue when being exposed to a mechanical load. In this case two measurements have been carried out, and compared. These differ through a small damage that has been introduced to the bone tissue in the second measurement.
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