Volume 105, Issue 7

Two flat hollow cylinders made of martensitic 9 wt.% Cr steels were creep deformed under in-service conditions typical of steam pipes at fossil-fuel fired power plants. Damage in the tubes was assessed through synchrotron X-ray microtomography by evaluating the shape, size and spatial-distribution of voids. The analysis of the size distribution of non-coalesced voids suggested that void growth is controlled by the plasticity constrained diffusional mechanism, a hypothesis verified by micromechanical simulations. A much higher void density was found in steel grade P91 compared to E911.

The 3D phase distribution of cement pastes evolves during hydration and controls the rheology and mechanical properties of the paste. Synchrotron powder-diffraction micro-tomographic imaging is here employed to assess the cement phase spatial distribution in a totally non-invasive way. This technique can be used to produce distribution maps of the phases present in the hydrating cement paste. The method is applied to an ordinary Portland cement, hydrated in pure water or in the presence of nucleation seeds. The quantitative description of the phase spatial distribution by radial distribution functions allows the discrimination of different nucleation mechanisms.

For the engineering of foamed food products, knowledge about the foam structure as well as about its dynamics and stability are of critical importance. Using fast tomography in the laboratory as well as ultra-fast phase-contrast synchrotron tomography accurate information about the entire pore distribution in milk protein foams is obtained almost instantaneously. This study displays the four-dimensional structural dynamics of milk-protein foam decay over time with unparalleled temporal and spatial resolution of the measurement data down to 1 s scan time (for 11 μm voxel sampling) and to 2.7 μm voxel sampling (for 2 s scan time). Pore size investigation is applied to a 15 min cine-tomography series monitoring the four-dimensional time decay of β-lactoglobulin foam, providing new insights into the dynamics of liquid protein foams.

We investigated the hydrogen distribution spatially and temporally in technical iron at room temperature. Samples were charged electrochemically and subsequently analysed by means of neutron radiography and tomography. The radiographic images allowed for a time-resolved analysis of hydrogen fluxes. The three-dimensional distribution of hydrogen measured by neutron tomography delivered valuable information for the damage analysis of hydrogen-induced cracks. For the first time hydrogen concentration gradients inside the material could be detect directly together with the cracks. The neutron radiography and tomography results were gained at the Research Reactor BER II of the HZB in Berlin.

Specimens of carbon or glass fiber reinforced polymer can be imaged using both conventional laboratory X-ray micro-computed tomography equipment and synchrotron light sources. The image quality when using intense (partially) coherent synchrotron light is still superior, especially when applying phase-retrieval algorithms. In the resulting volume images, the fiber direction distribution and other mechanically relevant parameters such as volume fractions or layer thickness can be determined. In this contribution, we will demonstrate how fiber direction results can be used to detect regions with locally different fiber orientations in carbon or glass fiber reinforced polymer which arise in the molding process of such samples. To this end, we evaluate the three-dimensional fiber orientation tensor locally across the thickness of different specimens. For each resulting individual layer, we can automatically detect the layer thickness and the preferred fiber direction. These methods have been successfully applied to various commercial specimens. We will demonstrate results on volume images of samples from both synchrotron and laboratory micro-computed tomography and discuss the specific advantages and disadvantages in this application.

The spatial resolution of diffractive imaging techniques depends upon the numerical aperture of the detected scatter rather than any image forming optics. Fresnel coherent diffractive imaging has been developed over the past decade as a means for examining regions of interest within continuous samples and for overcoming many of the stagnation issues traditionally associated with coherent diffractive imaging. Ptychography meanwhile has been developed independently as a method of reconstructing the transmission function of extended objects from diffraction data recorded using a sequence of multiple overlapping probes on the sample. The relatively recent combination of these two methods has been found to provide substantial benefits over either of the two techniques when applied separately. The experimental requirements and basic principles of ptychographic Fresnel diffraction tomography are reviewed in this paper.

This paper describes the modern tool of neutron tomography as an alternative and complement to the more common X-ray options and its potential for applications in materials research and engineering. Based on our own practical experiences, the challenges, success and limitations of neutron tomography are sketched and the potential for further improvements and methodical extensions is described. Using the performance at dedicated neutron imaging beam lines, there are many new aspects which only can be made available with neutron methods such as energy-selective imaging near Bragg edges, imaging with polarized neutrons and even imaging in the resonance region. Therefore, it is of high importance to get more and easier access to suitable beam ports at advanced neutron sources to make methodical progress and to attract more scientific and industrial users.

The mean number of pores per inch ( PPI value) is one of the most important geometric characteristics of cellular materials such as open or closed foams. It is defined as the number of pores (cells) along a straight test line related to the line length. Counting cells along a test line sounds very simple, but on the surface of an open foam specimen it is often hard to decide whether a cell hits the line or not. Thus, there exists no quick and safe method to estimate the PPI value from an optical image taken from the specimen's surface. In this article, we present a very efficient method of estimating the PPI value of foams from optical dark-field images of the surface of a foam sample. The method is based on the computation of the spectral density of the (two-dimensional) dark field images. It turns out that the radius of the first interference ring in the spectral density is proportional to the PPI value. The constant of proportionality can be determined from geometric models for open foams or analysis of three-dimensional images of foam samples. These techniques allow calibration of the estimation of the PPI value from the spectral density of two-dimensional dark field images.

Pre-clinical animal models are commonly used to evaluate the osteogenic potential of bone grafting materials in-vivo. Based on the histology analysis, the currently commercially available bone grafting materials show comparable results with respect to biocompatibility, incorporation and remodeling. In the present pilot study we introduce a methodology to compare calcium phosphate-based bone grafting materials from world-leading companies in clinical trials and analyze them by means of established histology and synchrotron radiation-based micro computed tomography (SRμCT). The results indicate that the morphology of the bony structures depends on the selected bone grafting material and that an arbitrarily selected histological slice can lead to misleading conclusions. Complementary μCT data can become the basis for the identification of a representative slice. The registration of the selected histological slice with its counterpart in the three-dimensional μCT dataset was performed both visually and automatically with well comparable results. This registration allows for the compilation of a joint histogram to identify anatomical features, which can neither be extracted from histology nor from μCT data on their own. Accordingly, μCT will become an integral part of studies on the efficacy of bone augmentation materials and beyond.

Selective laser melting allows the fabrication of NiTi implants with pre-defined, complex shapes. The control of the process parameters regulates the arrangement of the granular microstructure of the NiTi alloy. We prepared specimens with elongated grains, which build a sound basis for diffraction contrast tomography experiments using synchrotron radiation and for electron backscatter diffraction measurements. Both approaches reveal the orientation and size of the individual grains within the specimen. Still, electron backscatter diffraction is confined to two-dimensional cross-sections while diffraction contrast tomography reveals these microstructural features in three dimensions. We demonstrate that the grains in the selective laser melted specimen, which are oriented along the building direction, do not exhibit a well-defined planar grain orientation but are twisted. These twisted grains give rise to diffraction spots observable for several degrees of specimen rotation simultaneously to the acquisition of tomography data.

This paper is dedicated to the analysis of 3D data of carbon fiber reinforced silicon carbide ceramics. In the production process of C/SiC, a porous carbon preform reinforced with bundles of carbon fibers is infiltrated with liquid silicon at approximately 1 500 °C. The reaction between liquid silicon and carbon creates a layer of silicon carbide while the silicon vanishes almost completely. This material is able to withstand extremely high temperatures and it is extremely tough with respect to fracture. To increase the efficiency of the costly and time consuming production process, methods for monitoring the quality of the material are helpful. For instance, the thickness of the silicon carbide layer is a valuable measure. Moreover, due to different coefficients of thermal expansion of the components, typically cracks appear during the production process. For effective analysis 3D high resolution image data are necessary that can be acquired by synchrotron computed tomography. In a first image processing step, we segment the 3D image data with a convex optimization approach incorporating spatial regularity. Further, we work on the detection of cracks using an eigenvalue analysis of the 3D Hessian matrix determined in each pixel.