Papers by Keyword: Stereology

Abstract: The observation, description, and ultimate prediction of causal connections between processing and resulting macroscopic properties stand at the heart of Materials Science and Engineering. To that end, the microstructure is the subject of intense examination, as it is ultimately responsible for the observed emergent behavior. As a result, many of the scientific or technical questions that we strive to answer boil down to quantitatively studying the—sometimes subtle—effects of processing on the microstructure in terms of known or hypothesized thermodynamic and kinetic phenomena. This statement is naturally also true in the case of hot isostatically pressed powder metallurgy tool steels. In the 50 years since the process' popularization, many parameters have been identified as relevant to microstructure formation during consolidation. Among these process variables, the powder solidification structure distribution is probably the last to join the list. Dendritic solidification during the atomization of relatively massive particles produces slightly elongated carbides. On the other hand, cellular solidification in smaller powder particles is responsible for smaller and more angular carbides. Characterizing powder solidification structure as a function of particle size presents two main challenges: First, the assessment relies on examining cross-sections of the powder particles, which are most likely non-diametric. And, second, the manual identification exercise is tedious and highly subjective. In this work, we show how we achieve fast and reliable powder structure solidification distributions using deep learning combined with state-of-the-art stereology reconstruction techniques.

Abstract: We analyzed histological data statistically describing the distribution of orientations of vascular smooth muscle cells (VSMC) within porcine aorta. The data were correlated with the fractions of actin, desmin, vimentin, elastin and collagen within the same samples. In samples with more contractile VSMC and less elastin, the symmetrical helices of VSMC were arranged closely to each other and they were more concentrated than in samples with fewer actin-and desmin-positive VSMC and more elastin. The findings are suitable for microstructurally-motivated biomechanical modeling of porcine aorta under normal conditions.

Abstract: Finite element modelling (FEM) of machining is a widely applied way to get information about the phenomena occurring during the cutting process. This paper discusses experimental work and FEM analysis to investigate the mechanism of CK45 (1.0503) carbon steel chip formation during orthogonal turning process. Local strain in cutting zone is estimated by measurement of deformation of metallographic cut using stereological evaluation of the gain boundary orientation. Estimated local strain in cutting zone was compared to deformation analysis for orthogonal cutting was made, based on simulation results in numerical modelling software DEFORM 2D. Stress, temperature, tool wear is also discussed in the last part of this paper.

Abstract: Technological processes of machining lead to plastically deformation of workpieces. Therefore it is needful to know influence of machining to machined material. The area of plastically deformation caused by friction of tool to machined surface was analysed. Local strain in structure was estimated by measurement of deformation of grains on metallographic cut using stereology. Local plastic deformation in deformation zone around the surface of drilled holes, local plastic deformation in deformation zone near the surface of milled workpiece and local plastic deformation near the surface of turned workpiece were investigated. The working piece was bulk from carbon steel CK45 (1.0503). Local plastic deformation was observed in case of drilling and turning, in case of milling no deformation of surface was present.

Abstract: The morphology ZrO₂-Ti composites depends on used powders substrates, methods of forming and sintering conditions. In this study a composite from the nanosize ZrO₂ powder stabilized by 3 mol% Y₂O₃ and 3 vol. % Ti powder with particle size about 15 μm was prepared. A composite material was formed by uniaxial pressing. Sintering process was conducted in an argon atmosphere at 1300°C with retention time 2h. The selected physical properties of the green body and sintered ZrO₂-Ti composites were determined by Archimedes method. The microstructural characterization was carried out using the x-ray diffraction and the scanning electron microscope (SEM) with EDS analysis. Stereological analysis by using computer programs was supported. The SEM observation and EDS analysis of the cross-section of the samples confirmed that the Ti particles are distributed homogenously in analysed areas. The EDS analysis revealed partial solution of titanium in ZrO₂ matrix. Moreover, the x-ray diffraction exposed the existence of tetragonal zirconium oxide and titanium or a new phase from Ti-Zr-O system. The stereological analysis showed similarity between the starting particles of Ti powder and particles of titanium in the composite matrix.

Abstract: In the article authors presented digital measurement problem of the object on the 3D images of the microstructures. As a research material were used the micro tomography image of the probe C45 steel with WC-Co-Al₂O₃ surface layer. Due to relatively low contrast between the surface layer and the root material, and lack of sharp edges, some of the methods for automatic threshold indication may give biased results. Following the initial selection of the many methods of automatic binarization two of them and interactive method was selected to carry out comparative studies. The analysis included assessment of the layer thickness, number of detected objects and total volume of all detected objects.

Abstract: In this work we demonstrate the application of stereology-based image analysis for the characterization of highly porous cellular ceramics (alumina foams) prepared by biological foaming with yeast and subsequent drying (80-105 °C) and firing (1570 °C). It is shown that the ceramics prepared usually have total porosities in the range 78-84 % and that the porosities made up by large pores (volume fraction of foam bubbles) are usually in the range 58-75 %. Further it is shown that the mean chord length and the Jeffries size, i.e. pore size measures related to the interface density and the mean curvature integral density, respectively, are relatively close to each other (usually 0.8-1.4 and 0.8-1.2 mm) with a ratio close to unity (0.9-1.3) and that the mean surface-to-surface distance of pores gives a realistic picture of the average pore wall thickness (usually 0.46-0.69 mm). Using a special processing variant (excess ethanol addition) it is possible to obtain microstructures with lower porosity (total porosity 68-70 %, foam bubble volume fractions 50-56 %) and smaller pore size (approx. 0.5 mm). Absolute errors are calculated using normalized deviations corresponding to 95 % reliability in the Student distribution and the standard errors for the quantities in question (both observed and estimated). Relative errors are found to be below 12 % when the number of measurements is of order 400-1000.

Abstract: Method of local strain estimation based on evaluation of relative surface area of grain boundaries in deformed and undeformed state is used very often [. Unfortunately, this method requires information about the parameter of structure in case of zero value of initial deformation. Mentioned parameter is unknown in most cases. In addition, value of parameter of structure depends on grain size and it can change in volume of material.

Abstract: Final properties of plastic deformed parts of workpieces are affected by production technological processes. Therefore it is needful to know detailed structure changes of plastic deformed material caused by machining - grinding, drilling etc. Friction of tool to work surface caused one of three areas of plastic deformation in cutting zone. It has great influence to quality of work surface and local mechanical properties of surface layer of workpiece. Influence of drill wear to local plastic deformation in deformation zone around the surface of drilled holes was investigated. Two types of cutting tools were used: high speed steel drill IZAR HSSCO with diameter 6,0 mm surface hardened by boriding and the same one without boride layer. Standard cutting parameters were used. During the machining process, axial component of cutting force and torque were observed. The work piece was bulk from carbon steel Ck45 (1.0503). Wear of the tool was estimated as a wide of wear on tool flank. The local strain in analysed place of probes on their sections was obtained by stereological measurement of degree of grain boundaries orientation, which is proportional to grain boundaries deformation degree. Estimation of grain boundary orientation degree leads to determination of local plastic deformation in arbitrary place of workpiece. These results lead to detailed analysis of material structure changes caused by drilling from which local mechanical properties result.

Abstract: Final properties of formed steel or another alloy pieces are affected even by plastic deformation of material. Therefore it is needful to know detail structure changes of material under conditions of plastic deformation caused by forming, grinding, drilling etc. Estimation of the deformation based on its observable macroscopic effects doesn’t correspond fully with microscopic structural changes in whole volume of deformed parts and such estimation is quite impossible in case if only surface layers are deformed. It is possible to obtain value of strain by measurement of grain boundary deformation. Effect of grains boundaries self-orientation caused by grains deformation can be identified on metallographic cut. Stereological measurement of degree of grain boundary orientation is relatively simple if axes of orientation are known (as it is in most of deformation processes). Preferred direction of grains boundaries orientation is the same as direction of deformation; however orientation is not the same thing as deformation. Therefore model of conversion of degree of grain boundary orientation to deformation based on an idealized shape of grains has been proposed. This conversion model is independent on an initial grain size – strain depends only on the shape of the grain and does not depend on its dimension. It allows experimental estimation of local plastic deformation by means of measurement of grain boundary orientation in various areas of plastically deformed parts.