Fredrik Forsberg

3D micro-scale deformations of wood in bending: Synchrotron radiation μCT data analyzed with digital volume correlation

A micro-scale three-point-bending experiment with a wood specimen was carried out and monitored by synchrotron radiation micro-computed tomography. The full three-dimensional wood structure of the 1.57x3.42x0.75mm(3) specimen was reconstructed at cellular level in different loading states. Furthermore, the full three-dimensional deformation field of the loaded wood specimen was determined by digital volume correlation, applied to the reconstructed data at successive loading states. Results from two selected regions within the wood specimen are presented as continuous displacement and strain fields in both 2D and 3D. The applied combination of synchrotron radiation micro-computed tomography and digital volume correlation for the deformation analysis of wood under bending stress is a novel application in wood material science. The method offers the potential for the simultaneous observation of structural changes and quantified deformations during in situ micro-mechanical experiments. Moreover, the high spatial resolution allows studying the influence of anatomical features on the fracture behaviour of wood. Possible applications of this method range from bio-mechanical observations in fresh plant tissue to fracture mechanics aspects in structural timber.

3D deformation and strain analysis in compacted sugar using x-ray microtomography and digital volume correlation

Understanding the displacement of granular beds under compaction is important for a range of industrial, geological and civil engineering applications. Such materials exhibit inhomogeneous internal displacements including strain localization, which mean that a method for the in situ evaluation of internal 3D displacement fields at high spatial resolutions would be a major development. This paper presents results from the compaction of a cylindrical bed of sugar, with diameter 7.0 mm and height 8.2 mm, using x-ray microtomography to evaluate the internal structure and digital volume correlation to calculate 3D displacement information from these data. In contrast to previous studies, which generally track a small number of marker particles, the research here uses the natural structure of the sugar to provide a random pattern for 3D image correlation, allowing full-field information to be captured. The results show good agreement when compared with a well-established 2D image correlation technique; moreover, they indicate structural features associated with deformation of granular materials that would not necessarily be observed in a 2D slice.

Estimation of affine transformations directly from tomographic projections in two and three dimensions

This paper presents a new approach to estimate two- and three-dimensional affine transformations from tomographic projections. Instead of estimating the deformation from the reconstructed data, we introduce a method which works directly in the projection domain, using parallel and fan beam projection geometries. We show that any affine deformation can be analytically compensated, and we develop an efficient multiscale estimation framework based on the normalized cross correlation. The accuracy of the approach is verified using simulated and experimental data, and we demonstrate that the new method needs less projection angles and has a much lower computational complexity as compared to approaches based on the standard reconstruction techniques.

Three-dimensional selective imaging of sound sources

A technique for 3-D selective imaging of sound sources is described analytically and demonstrated experimentally. One-dimensional recordings of the acoustic field is measured using laser vibrometry ...

Precision measurements of linear scattering density using muon tomography

We demonstrate that muon tomography can be used to precisely measure the properties of various materials. The materials which have been considered have been extracted from an experimental blast fur ...

Tomographic Reconstruction of 3D Ultrasound Fields Measured Using Laser Vibrometry

A method for obtaining the amplitude and phase distribution of an ultrasound field in air, using laser vibrometry and computed tomography, is described. Radiating ultrasound transducers causes pres ...

Internal deformation and velocity field measurements by use of digital speckle radiography

Using X-rays as information carriers it is possible to obtain data about motion inside an object that is opaque to visible light. An image correlation algorithm can be applied to a set of two X-ray images taken sequentially during a process, where the interior of the object is in motion. A displacement field describing the projected intermediate motion is thus obtained to sub-pixel accuracy. If this image set is expanded to contain several pictures separated in time, together describing the whole process, the images can be sequentially correlated to obtain a dynamic displacement field. In this paper, dynamical displacement field measurements have been carried out on two different objects, the first being a silo, where the motion of the flowing material in the center plane is investigated. In the second case, the motion in a layer of glue between two wooden plates is examined during a process where a shearing force acts on the system. The plane in which the measurements are carried out is defined by the use of a contrast agent, usually a tungsten powder seeding. The obtained displacement field, together with the known intermediate time interval between exposures, gives the velocity field in the seeded plane. The results show good agreement with the expected motion in the respective processes, but also provide evidence of behavior that would be undetectable using other existing techniques. A third experiment has also been carried out on a material requiring no contrast enhancing media. These measurements were performed on a chicken thigh being deformed by an external force. The results will be discussed in relation to their reliability and applicability. Further, the direction of future research will be indicated.