Papers by Keyword: Homogeneity

Abstract: The studies showed that as a result of radial-shear rolling (RSR) in the temperature range of 850-650°C the formation of a quasi-globular ultrafine grain-subgrain structure with a size of structural elements of about 0.5-0.7 μm is observed in near β titanium alloy Ti-5Al-5V-5Mo-1Cr-1Fe. Subsequent annealing (aging) in the temperature range of 450°C for 5 hours leads to the decomposition of the β-phase matrix deformed during the rolling process with the formation of nanosized acicular precipitates of the martensitic α" phase along with finely dispersed inclusions of α phase particles preserved after rolling. The formation of such ultrafine-grained (UFG) structure leads to a significant (more than 25%) increase in the strength properties of the alloy compared to the initial state while maintaining sufficient ductility (~5%). Also obtained by the method UFG titanium alloy exhibits a high fatigue strength under very high cycle loading (fatigue strength based on 10⁸ cycles exceeds 700 MPa).

Abstract: The practical expediency of the study of physical and mechanical properties of concrete, received from the mix, exposed at its feeding to the point of placement to the transportation with the inertia conveyor by means of original technology, which shows its competitiveness at factories producing precast concrete units, is proved. The experimental procedures of the research performed by the authors, where they analyzed the process of transportation relating to the use of ready-mix concrete on the dense aggregate, are described. The data on the effect of received previously rational values of the major parameters of engineering process studied (the parameters of asymmetric oscillations of work member of the conveyor and the thickness of the mix layer moved by it) both on the homogeneity of fresh concrete and the strength and strength homogeneity of hardened concrete are represented and analyzed.

Abstract: Design, preparation and testing of fibre-cement composites are a task of wide range of research workplaces and universities in our country and abroad. However, a question on homogeneity of all cement matrix components and mainly optimal dispersion of fibre reinforcement in a mixture has not been yet solved sufficiently. Within testing of properties of such designed composites there is usually a realized fact, that variability of these properties is distinctive mainly for the reason of uneven dispersion of commonly used fibres in a whole matrix volume. Elimination of this phenomenon could be achieved by means of a design of the optimal homogenization process of dry mixture components with fibre reinforcement. The aim of research works was to find suitable homogenization techniques, design of mixing process and optimal dosing of individual components. By means of these actions it is possible to achieve the best dispersion of selected fibre types, both metal and non-metal, in fine-grained cementitious matrixes, which is subsequently verified in hardened composites at first by non-destructive and then by destructive methods. Four different fibre-cement mixtures were chosen as representatives for commonly used reinforcement in fibre-cement composites and test specimens with a thickness of 40 mm were prepared using processes suitable for the specific fibre reinforcement. At the first stage non-destructive testing by means of ultrasound waves was carried out at first on a compact test slab with dimensions 500 x 500 x 40 mm and subsequently on individual test specimens with dimensions 250 x 40 x 40 mm, cut from the test slab according to a designed pattern. At the second stage destructive testing of test specimens was performed, mainly evaluation of flexural strength with 4-point bending and subsequently preparation of thin sections from the failure area for observation by means of polarizing microscopy. A purpose of all these research works is finding of correlation between testing by means of destructive and non-destructive methods.

Abstract: In design of the electronic device, FEM analyses considering the creep deformation of solder joints in-situ should be conducted to evaluate the strength reliability. The indentation test is one of effective method to evaluate the creep deformation in microscopic region. However, the result obtained by the indentation test does not coincide with that obtained by the tensile creep test. To solve the problem, the method to determine the suitable area for the indentation test had also been proposed by using the numerical test. To apply the proposed method for the actual indentation test, the homogeneity of specimen should be considered. In this paper, the analyses of the proposed indentation tests were conducted by using the homogeneous and inhomogeneous specimen models of Sn-3.0Ag-0.5Cu. Three types of the deformation behavior were given for the initial phase and the indenter was pushed into in the specimen at the three locations. As a result, it was found that there was not difference in the distribution of the principal stress caused by variation in the indent location. However, the proposed method can successfully determine the reference area except for the case when the deformation behaviors of the constituent phases have a large difference.

Abstract: An Al-3% Mg-0.2% Sc alloy was subjected to annealing or solution treatment and further processed by HPT at room temperature. Microhardness measurements were taken along the middle-sections of the discs and they demonstrated that a very substantial hardening is achieved during HPT processing regardless of the initial heat treatment. Hardness values of ~200 Hv were recorded at the edge of the samples although the microhardness distribution remained inhomogeneous along the diameters of the discs after 20 turns of high-pressure torsion. In addition, the microhardness of the solution treated Al-Mg-Sc samples continued to increase with the equivalent strain imposed by the anvils even after 30 turns of HPT processing whereas the hardness at the edges of the annealed discs saturated after 10 turns. These differences in the hardness evolution are attributed to the higher Mg content in solid solution in the case of the solution treated samples and its influence on delaying the recovery rate of this aluminium alloy.

Abstract: Polymer-based nanotextiles are produced by electrostatic spinning. Nanospider technology developed by Prof. Jirsák at Technical University in Liberec also uses electrospinning. This technology has been modified over time. The aim of this paper is to compare two modifications of this technology and determine which one is more suitable for the production of nanotextiles for civil engineering applications. The comparison was performed using images from scanning electron microscope and measurements of weight per square meter of the fabrics. For the civil engineering applications it is important for the fabric to be as homogeneous at macroscale as possible, so that properties of different parts of the fabric are approximately equal. We have found that modification of Nanospider technology using rotating roller provides better results than a modification which involves a movable slider.

Abstract: Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) is a fine-gained composite material achieving both high compressive and tensile strengths. Values of compressive strength, tensile strength and bending strength depend not only on a composition of the mixture itself, but also on the border conditions of the setting of the test, it means the support type, the loading rate etc. UHPFRC is used not only in European countries (Germany, France, Holland), but in distant countries (USA, Japan, Australia), too. In the Czech Republic is UHPFRC produced mainly in laboratories. The first using of UHPFRC for the real construction in the Czech Republic was a production of lost shuttering slabs that were used at the reconstruction of the raod-bridge across R10 highway. These results of the lost shuttering slabs became the base of a more detailed research of the homogeneity of the steel fibre distribution and its impact on load bearing capacity of the UHPFRC elements. Experimental beams with a different volume fraction of steel fibres were made and tested on the basis of the determined results of a nonhomogeneous fibre distribution at the cross section of lost shuttering slabs. Then the layered beams with a controlled steel fibre distribution at the cross section were made and tested too. The test results together with a description and characterization of the behaviour of tested homogeneous beams with different volume fraction of the steel fibres and functionally layered beams are published in this paper.

Abstract: In this paper, for countable homogeneous Markov process, we prove strong Markov property defining by [2] are valid. So for an arbitrary countable homogeneous Markov process is a strong Markov process.2000 Mathematics Subject Classification. Primary 60J25, 60J27.

Abstract: Load-bearing capacity of fine grained cement-based composite materials UHPFRC depends on the homogeneity of the steel fiber distribution at cross section. The homogeneity of the steel fiber distribution has significant effect to the mechanical properties of UHPFRC elements, especially at tensile strength in bending. The load-bearing capacity depending on the homogeneity of steel fibers at the permanent formwork slabs made from UHPFRC is shown in this paper.

Abstract: The article presents industrial conditions of manufacturing multi-component heterogeneous mixtures of granular materials. The study analyzed the production technology and devices used for production such as storage siloes, an impact screen, a cyclone separator, a shaving and dust extractor, a screw mixer, a tensometric weigh, a bucket conveyor. A division and the successive stages of manufacturing process has been presented: unloading, receipt and storage of raw materials, quality control of components, technology cleaning and sorting of raw materials, dosage and mixing of feed material, bagging, storage, extraction processes and evaluation of homogeneity in a fodder mixing plant. Moreover the methods of assessing the homogeneity of the multi-component heterogeneous mixtures has been presented. The research was conducted in industrial conditions.