Image segmentation is a crucial step of almost any Digital Rock workflow. In this paper, we propose an approach for generation of a labelled dataset and investigate an application of three popular convolutional neural networks (CNN) architectures for segmentation of 3D microtomographic images of samples of various rocks. Our dataset contains eight pairs of images of five specimens of sand and sandstones. For each sample, we obtain a single set of microtomographic shadow projections, but run reconstruction twice: one regular high-quality reconstruction, and one using just a quarter of all available shadow projections. Thoughtful manual Indicator Kriging (IK) segmentation of the full-quality image is used as the ground truth for segmentation of images with reduced quality. We assess the generalization capability of CNN by splitting our dataset into training and validation sets by five different manners. In addition, we compare neural networks results with segmentation by IK and thresholding. Segmentation outcomes by 2D and 3D U-nets are comparable to IK, but the deep neural networks operate in automatic mode, and there is big room for improvements in solutions based on CNN. The main difficulties are associated with the segmentation of fine structures that are relatively uncommon in our dataset.

Excited-state absorption (ESA) in various bismuth-doped fibers (BDFs) was investigated. No significant ESA in IR emission bands of Bi-doped germanosilicate and phosphosilicate fibers was found. Considerable ESA was observed in Bi-doped aluminosilicate fibers at 800–1700 nm. The ESA spectra of the aluminosilicate BDFs with different bismuth concentration were measured at room and 77 K temperature. Significant dependence of the ESA on the bismuth concentration and the fiber temperature was found.

Small scale fatigue tests aimed at determining the S-N diagram and the Miner Index to be adopted for fatigue damage assessment of railway axles were carried out within the frame of the frame of the research activities of EU funded EURAXLES project. Fatigue tests performed on steel grades EA4T and EA1N adopted by the European EN13103/13104 standards with both constant and variable amplitude loading are reported. The variable amplitude loading fatigue tests were carried out by using loading spectra derived from actual load measurements of fatigue bending moment in railway axles under significant service conditions. The consistent version of Miner's rule (according to the FKM-Guideline) with and allowable damage sum D(crit) = 0,3 adopted in combination with 2.5% percentile (p2.5%) of the S-N curve derived experimentally with small specimens proved to be adequate as design criterion, thus enabling the transferability of small scale fatigue tests to full scale railway axles that would lead to improved fatigue resistance of railway axles with new designs

The PDF file of this paper is in Russian. The first application of digital rock technology (digital core analysis) with direct hydrodynamic modeling based on density functional theory for the Achimov formation is described. The technology consists of imaging core samples by X-ray microtomography, construction of corresponding digital rock models of pore space geometry, and multiphase hydrodynamic simulation on a pore scale by the density functional method. Despite the extremely low permeability values (less than 1 μd), digital measurements of relative permeability curves were completed successfully for model oil and water in steady-state flow mode whereas laboratory measurements in steady-state flow regime were unfeasible for the studied samples. The required spatial resolution of the digital rock models for the studied samples was about 1 μm and higher. At the same time, for a reasonable selection of a representative sample, it is desirable to conduct a larger sample scan with a coarser resolution. For the first time in the industry, a direct two-phase relative permeability simulation was performed on a record-size model of 1300 × 1300 × 1500 voxels. Also, for the first time, two-phase filtration experiments were carried out on a core miniplugs in the permeability range of less than 1 μd.

We present an approach for 2D-to-3D mineralogical information propagation and preliminary results of its implementation. An X-ray microtomography (microCT) scanner is used to obtain a 3D microstructural image of the sample. A scanning electron microscope (SEM) equipped with an energy-dispersive X-ray (EDX) detector provides a supervising 2D mineral map of a rock sample cross section. The 2D and 3D images are then registered using a surface-based algorithm, naturally taking into account specifics of said data. The overlapping area of the images is then used as a training set for supervised mineralogical segmentation of the full 3D sample.

The brittle failure assessment for five pressurized water reactor pressure vessels (RPV) of German nuclear power plants (NPP) has been revisited according to an advanced state of the art. Besides of recent innovation in fracture toughness curves and reference temperatures being already in the codes, also the effect of loss of constraint had to be considered when fracture toughness values determined from deep cracks in fracture toughness specimen with high multi-axial state of stress were transferred to crack configurations in the component. Thus, the available concepts were compared for their fitness for purpose, i.e. for their ability to give a fracture toughness representative to the crack configuration or flaw postulate in the component. The results of the investigation reveal a significant lower constraint in the component resulting in increased fracture toughness and showing that the brittle failure assessment based on the high constraint fracture toughness from the standard specimens can be very conservative. For consideration of the constraint conditions in the component besides the deterministic T-stress parameter also probabilistic local approach concepts based on the Weibull model were used which have the advantage of considering both the local stress strain field and the material volume under high loading. The loss of constraint was determined for several flaw postulates in the leading situations on the RPV being the coolant inlet nozzle corner and the flange joint. A considerable loss of constraint was demonstrated for flaw postulates with broken clad in the ferritic nozzle corner. Also in the flange joint the loss of constraint is evident for small flaws. In addition, for flaw postulates under the intact cladding the loss of constraint is remarkably higher than with broken postulated cladding. In summary, with the measured material toughness and the significant loss of constraint a considerable inherent margin against brittle failure can be demonstrated for the investigated load cases.